Integrated Aedes management for the control of Aedes-borne diseases

EVITA Dengue: a cluster-randomized controlled trial to EValuate the efficacy of Wolbachia-InfecTed Aedes aegypti mosquitoes in reducing the incidence of Arboviral infection in Brazil

Background

Arboviruses transmitted by Aedes aegypti including dengue, Zika, and chikungunya are a major global health problem, with over 2.5 billion at risk for dengue alone. There are no licensed antivirals for these infections, and safe and effective vaccines are not yet widely available. Thus, prevention of arbovirus transmission by vector modification is a novel approach being pursued by multiple researchers. However, the field needs high-quality evidence derived from randomized, controlled trials upon which to base the implementation and maintenance of vector control programs. Here, we report the EVITA Dengue trial design (DMID 17-0111), which assesses the efficacy in decreasing arbovirus transmission of an innovative approach developed by the World Mosquito Program for vector modification of Aedes mosquitoes by Wolbachia pipientis.

Methods

DMID 17-0111 is a cluster-randomized trial in Belo Horizonte, Brazil, with clusters defined by primary school catchment areas. Clusters (n = 58) will be randomized 1:1 to intervention (release of Wolbachia-infected Aedes aegypti mosquitoes) vs. control (no release). Standard vector control activities (i.e., insecticides and education campaigns for reduction of mosquito breeding sites) will continue as per current practice in the municipality. Participants (n = 3480, 60 per cluster) are children aged 6–11 years enrolled in the cluster-defining school and living within the cluster boundaries who will undergo annual serologic surveillance for arboviral infection. The primary objective is to compare sero-incidence of arboviral infection between arms.

Discussion

DMID 17-0111 aims to determine the efficacy of Wolbachia-infected mosquito releases in reducing human infections by arboviruses transmitted by Aedes aegypti and will complement the mounting evidence for this method from large-scale field releases and ongoing trials. The trial also represents a critical step towards robustness and rigor for how vector control methods are assessed, including the simultaneous measurement and correlation of entomologic and epidemiologic outcomes. Data from this trial will inform further the development of novel vector control methods.

Trial registration

ClinicalTrials.govNCT04514107. Registered on 17 August 2020

Primary sponsor: National Institute of Health, National Institute of Allergy and Infectious Diseases

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-05997-4.

Oviposition dynamics of Aedes aegypti in Central Argentina

Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) is the vector of multiple arboviruses. To evaluate the association between environmental factors and the oviposition activity of Ae. aegypti in Argentina, data on the presence and abundance of eggs were collected using ovitraps, between September of 2018 and May of 2019, in the cities of Villa María, Río Cuarto and Salsipuedes (Córdoba province, Argentina). We analysed the relationships between oviposition and five environmental factors: Temperature, precipitation, vegetation cover, human population density and distance to sites with a potential high density of larval habitats, like cemeteries and trash dumps. Environmental factors' data were collected using satellite image products. The oviposition activity was randomly distributed in three cities. Using generalized linear mixed models, we show that the house where each ovitrap was placed was a source of variability in oviposition, suggesting the relevance of microsite factors and the importance of domestic control actions. Ae. aegypti oviposition was positively correlated with night-time temperature of the previous 3 weeks, and in a context-dependent manner, it was positively correlated with human population density, vegetation cover and precipitation. The consistency and magnitude of these relationships varied between cities, indicating that oviposition is related to a complex system of environmental variables.

Molecular action of larvicidal flavonoids on ecdysteroidogenic glutathione S-transferase Noppera-bo in Aedes aegypti

Background

Mosquito control is a crucial global issue for protecting the human community from mosquito-borne diseases. There is an urgent need for the development of selective and safe reagents for mosquito control. Flavonoids, a group of chemical substances with variable phenolic structures, such as daidzein, have been suggested as potential mosquito larvicides with less risk to the environment. However, the mode of mosquito larvicidal action of flavonoids has not been elucidated.

Results

Here, we report that several flavonoids, including daidzein, inhibit the activity of glutathione S-transferase Noppera-bo (Nobo), an enzyme used for the biosynthesis of the insect steroid hormone ecdysone, in the yellow fever mosquito Aedes aegypti. The crystal structure of the Nobo protein of Ae. aegypti (AeNobo) complexed with the flavonoids and its molecular dynamics simulation revealed that Glu113 forms a hydrogen bond with the flavonoid inhibitors. Consistent with this observation, substitution of Glu113 with Ala drastically reduced the inhibitory activity of the flavonoids against AeNobo. Among the identified flavonoid-type inhibitors, desmethylglycitein (4′,6,7-trihydroxyisoflavone) exhibited the highest inhibitory activity in vitro. Moreover, the inhibitory activities of the flavonoids correlated with the larvicidal activity, as desmethylglycitein suppressed Ae. aegypti larval development more efficiently than daidzein.

Conclusion

Our study demonstrates the mode of action of flavonoids on the Ae. aegypti Nobo protein at the atomic, enzymatic, and organismal levels.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01233-2.

Identification of novel-vector control target proteins of Aedes sp.: A Systems Network Biology Approach

Aedes is an important vector for various viruses that cause dengue, chikungunya and zika, which affect human health globally. Due to regular outbreaks of these diseases worldwide, there is a need to identify essential vector proteins that are critical for the survival of the vector, which may be targeted to control the spread of vector-borne disease (VBD). In silico computational methods involving comparative proteomics, analysis of orthologous proteins common amongst members of Aedes genus and protein-protein interaction (PPI) pathway were used to identify essential proteins that could act as novel therapeutic candidates. Twenty-three conserved proteins between A. aegypti and A. albopictus were identified from a BLASTP search with an e-value threshold of 0.005, and their PPI networks were constructed in the STRING database. The merged network was analyzed using various Cytoscape plugins viz. ClusterONE, Cytohubba and MCODE. Thirty-one hub proteins were identified from the system's network biology analysis, and detailed data and literature mining were carried out. Twelve novel vector-control target proteins of A. aegypti, having no human homologs, were determined in the present study that can effectively act as potential therapeutic candidates for drug design and vaccine development.

Temporal Evaluation of Insecticide Resistance in Populations of the Major Arboviral Vector Aedes Aegypti from Northern Nigeria

To support evidence-based control measures, two Nigerian Aedes populations (BUK and Pantami) were characterised. Larval bioassay using temephos and deltamethrin revealed a significant increase in deltamethrin resistance, with LC50 of 0.018mg/L (resistance ratio compared to New Orleans, RR = 2.250) in 2018 increasing ~6-fold, by 2019 (LC50 = 0.100mg/L, RR = 12.5), and ~11-fold in 2020 (LC50 = 0.198mg/L, RR = 24.750). For the median deltamethrin concentration (0.05mg/L), a gradual decrease in mortality was observed, from 50.6% in 2018, to 44.9% in 2019, and 34.2% in 2020. Extremely high DDT resistance was observed, with <3% mortalities and LT50s of 352.87 min, 369.19 min and 406.94 min in 2018, 2019 and 2020, respectively. Significant temporal increase in resistance was observed towards ƛ-cyhalothrin (a type II pyrethroid) over three years. Synergist bioassays with diethylmaleate and piperonylbutoxide significantly recovered DDT and ƛ-cyhalothrin susceptibility respectively, implicating glutathione S-transferases and CYP450s. Cone bioassays revealed increased resistance to the PermaNet® 3.0, side panels (mortalities of 94% in 2018, 66.4% in 2019, and 73.6% in 2020), while full susceptibility was obtained with the roof of PermaNet® 3.0. The F1534C kdr mutation occurred in low frequency, with significant correlation between heterozygote genotypes and DDT resistance. This temporal increase in resistance is a major challenge for control of this vector of public health importance.

Evaluation of the effectiveness of BG-Sentinel and CDC light traps in assessing the abundance, richness, and community composition of mosquitoes in rural and natural areas

BACKGROUND

Vector-borne diseases are a major burden to public health. Controlling mosquitoes is considered the most effective way to prevent vector-borne disease transmission. Mosquito surveillance is a core component of integrated vector management, as surveillance programs are often the cornerstone for the development of mosquito control operations. Two traps are the most commonly used for the surveillance of adult mosquitoes: Centers for Disease Control and Prevention miniature light trap (CDC light trap) and BG-Sentinel trap (BioGents, Regensburg, Germany). However, despite the importance of the BG-Sentinel trap in surveillance programs in the United States, especially in the Southern states, its effectiveness in consistently and reliably collecting mosquitoes in rural and natural areas is still unknown. We hypothesized that BG-Sentinel and CDC light traps would be more attractive to specific mosquito species present in rural and natural areas. Therefore, our objective was to compare the relative abundance, species richness, and community composition of mosquitoes collected in natural and rural areas by BG-Sentinel and CDC light traps.

METHODS

Mosquitoes were collected from October 2020 to March 2021 using BG-Sentinel and CDC light traps baited with dry ice, totaling 105 trap-nights.

RESULTS

The BG-Sentinel traps collected 195,115 mosquitoes comprising 23 species from eight genera, and the CDC light traps collected 188,594 mosquitoes comprising 23 species from eight genera. The results from the permutational multivariate analysis of variance (PERMANOVA) and generalized estimating equation model for repeated measures indicate the BG-Sentinel and CDC light traps had similar sampling power.

CONCLUSION

Even though BG-Sentinel traps had a slightly better performance, the difference was not statistically significant indicating that both traps are suitable to be used in mosquito surveillance in rural and natural areas.

Global burden for dengue and the evolving pattern in the past 30 years

BACKGROUND

Dengue is the most prevalent and rapidly spreading mosquito-borne viral disease. We present the global, regional and national burden of dengue from 1990 to 2019 based on the findings from the Global Burden of Diseases, Injuries, and Risk Factors Study 2019 (GBD 2019).

METHODS

Based upon GBD 2019 dengue data on age-standardized incidence rate (ASIR), age-standardized death rate (ASDR) and age-standardized disability-adjusted life years (DALYs) rate, this study estimates and presents annual percentage change (EAPC) to quantify trends over time to assess potential correlates of increased dengue activity, such as global travel and warming.

RESULTS

Globally from 1990 to 2019, dengue incident cases, deaths and DALYs gradually increased. Those under 5 years of age, once accounting for the largest portion of deaths and DALYs in 1990, were eclipsed by those who were 15-49 years old in 2019. Age standardized incidence [ASIR: EAPC: 3.16, 95% confidence interval (CI): 2.90-3.43], death (ASDR: EAPC: 5.42, 95% CI: 2.64-8.28) and DALY rates (EAPC: 2.31, 95% CI: 2.00-2.62) accelerated most among high-middle and high sociodemographic index (SDI) regions. South-East Asia and South Asia had most of the dengue incident cases, deaths and DALYs, but East Asia had the fastest rise in ASIR (EAPC: 4.57, 95% CI: 4.31, 4.82), while Tropical Latin America led in ASDR (EAPC: 11.32, 95% CI: 9.11, 13.58) and age-standardized DALYs rate (EAPC: 4.13, 95% CI: 2.98, 5.29). SDI showed consistent bell-shaped relationship with ASIR, ASDR and age-standardized DALYs rate. Global land-ocean temperature index and air passenger travel metrics were found to be remarkably positively correlated with dengue burden.

CONCLUSIONS

The burden of dengue has become heavier from 1990 to 2019, amidst the three decades of urbanization, warming climates and increased human mobility in much of the world. South-East Asia and South Asia remain as regions of concern, especially in conjunction with the Americas' swift rise in dengue burden.

Essential oil as a new tool for larvicidal Aedes aegypti: A systematic review

OBJECTIVE

The study aimed to describe the effectiveness of essential oil plants for Aedes aegypti mosquito vector control.

METHODS

This systematic review selection process following with 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Guideline. The source of the articles from databases international journal were Scopus, Pubmed, Scinapse and Google Scholar.

RESULT

Natural control management with essential oil is the way of alternative for larvicidal mosquito control especially A. aegypti. The essential oil for many plants can use for larvicidal against A. aegypti as Piper batle L., Tinospora rhumpii, Azadiractha indica, Persea americana, Piper aduncum, Leucas aspera, Eucaliptus camaldulensis, Ottonia anisum, Salvia Plebeian, Lantana camara, and Syzygium aromaticum with 100% mortality larvae A. aegypti at 48h.

CONCLUSIONS

The vector borne diseases must be used to integrate vector management control with essential oils plants.

Insecticide susceptibility status and knockdown resistance (kdr) mutation in Aedes albopictus in China

Background

Aedes (Stegomyia) albopictus (Skuse, 1894) is the main vector of dengue virus in China. The resistance to insecticides is a huge obstacle for the control of this species, and determining its resistance status and mechanisms in China is essential for the implementation of vector management strategies.

Methods

We have investigated the larval and adult resistance status of Ae. albopictus to deltamethrin in eight field populations in China. Mutations at the voltage-gated sodium channel gene, related to the knockdown resistance (kdr) effect, were detected by sequencing of PCR products. The eight field populations were examined for pyrethroid resistance using the World Health Organization standard bioassays, and the association between the mutations and phenotypic resistance was tested.

Results

The eight field populations of larvae of Ae. albopictus in China exhibited high resistance to deltamethrin; the RR₅₀ values ranged from 12 (ZJ) to 44 (GZ). Adult bioassay revealed that Ae. albopictus populations were resistant to deltamethrin (mortality rate < 90%), except ZJ population (probably resistant, mortality rate = 93.5%). Long knockdown time in the field populations was consistent with low mortality rates in adult bioassay. F1534S mutation showed increased protection against deltamethrin in all populations except BJ and SJZ populations, whereas I1532T mutation showed increased protection against deltamethrin in only BJ population.

Conclusion

There were different degrees of resistance to deltamethrin in field Ae. albopictus populations in China. The longest knockdown time and lowest mortality rate observed in Ae. albopictus population in Guangzhou indicate the severity of high resistance to deltamethrin. The patchy distribution of deltamethrin resistance and kdr mutations in Ae. albopictus mosquitoes suggests the necessity for resistance management and developing counter measures to mitigate the spread of resistance.

Graphical Abstract

Assessment of community support for Wolbachia-mediated population suppression as a control method for Aedes aegypti mosquitoes in a community cohort in Puerto Rico

Arboviral diseases transmitted by Aedes species mosquitoes pose an increasing public health challenge in tropical regions. Wolbachia-mediated population suppression (Wolbachia suppression) is a vector control method used to reduce Aedes mosquito populations by introducing male mosquitoes infected with Wolbachia, a naturally occurring endosymbiotic bacterium. When Wolbachia-infected male mosquitoes mate with female wild mosquitoes, the resulting eggs will not hatch. Public support is vital to the successful implementation and sustainability of vector control interventions. Communities Organized to Prevent Arboviruses (COPA) is a cohort study to determine the incidence of arboviral disease in Ponce, Puerto Rico and evaluate vector control methods. Focus groups were conducted with residents of COPA communities to gather their opinion on vector control methods; during 2018–2019, adult COPA participants were interviewed regarding their views on Wolbachia suppression; and a follow-up questionnaire was conducted among a subset of participants and non-participants residing in COPA communities. We analyzed factors associated with support for this method. Among 1,528 participants in the baseline survey, median age was 37 years and 63% were female. A total of 1,032 (68%) respondents supported Wolbachia suppression. Respondents with an income of $40,000 or more were 1.34 times as likely [95% CI: 1.03, 1.37] to support Wolbachia suppression than those who earned less than $40,000 annually. Respondents who reported repellant use were 1.19 times as likely to support Wolbachia suppression [95% CI: 1.03, 1.37]. A follow-up survey in 2020 showed that most COPA participants (86%) and non-participants living in COPA communities (84%) supported Wolbachia suppression during and after an educational campaign. The most frequent questions regarding this method were related to its impact on human and animal health, and the environment. Continuous community engagement and education efforts before and during the implementation of novel vector control interventions are necessary to increase and maintain community support.

Vector control is key to decrease the incidence of viral infections transmitted by Aedes mosquitoes, like dengue, but traditional control methods like insecticides and breeding sites reduction can be time-consuming, ineffective, and challenged by insecticide resistance. In the method known as Wolbachia suppression, male mosquitoes infected with the bacterium Wolbachia are released to mate with wild female mosquitoes. As the resulting eggs do not hatch, the mosquito population decreases over time. As public support is key to implement and maintain any vector control method, we assessed community support for Wolbachia suppression through focus groups and interviews with residents of Ponce, Puerto Rico, where a community cohort has been implemented. Support for this method in this population was high and increased after an educational campaign. Respondents with higher income and those who used repellent in the last 30 days were more likely to support Wolbachia suppression. Questions regarding the impact of this method on human and animal health, and the environment, were the most reported. Community engagement activities to increase the understanding of the method, including clear and specific information on health risk assessments, should be conducted before and during the implementation of Wolbachia suppression.

Efficacy of focal applications of a mycoinsecticide to control Aedes aegypti in Central Brazil

Entomopathogenic fungi can achieve important innovative outcomes for integrated mosquito control especially of Aedes aegypti, the key vector of arboviruses to humans in the tropics and subtropics. This study sought to design and to develop a simple dissemination device to attract and to infect gravid A. aegypti adults with a granular formulation of the ascomycete Metarhizium humberi IP 46, and to validate this device in the laboratory as well as in semi-field and field conditions. Hydrogel (polyacrylamide potassium polyacrylate) was confirmed to be a suitable substitute for water used in the device that attracted gravid females under field conditions. Females laid eggs on black polyethylene terephthalate carpet fixed in the device that also proved to be a suitable substrate for a granular formulation of fungal microsclerotia and/or conidia. The plastic device (29.5 cm high) was divided into a lower closed compartment with a water reservoir and an upper, laterally open but covered compartment with continuously hydrated gel and the fungal formulation attached to the carpet. The uppermost compartment permitted free circulation of mosquito adults. The device attracted both male and female A. aegypti. The fungal formulations of IP 46 propagules tested in the device were effective against adults in laboratory, semi-field, and field settings. Findings in the laboratory, semi-field, and especially in field conditions strengthen the value and utility of this innovative device for focal applications of a mycoinsecticide against this important mosquito vector.Key points• Low-cost and simple disseminating device for focal control of Aedes aegypti.• Granulized Metarhizium humberi IP 46 and hydrogel yield extended control.• Findings in field tests strengthen benefit of the device for focal application.

Evidence for the spread of the alien species Aedes koreicus in the Lombardy region, Italy

BACKGROUND

Aedes koreicus is a mosquito species characterized by marked anthropophilic behavior, and a potential vector of nematodes and viruses. It is native to East Asia, but its presence has recently been reported in many regions of Europe. In Italy, these mosquitoes had been detected in the northeast since 2011 and are now spreading towards the southwest of the country.

METHODS

In 2020, during a surveillance program for invasive mosquito species in the district of Bergamo (Lombardy Region, Italy), about 6000 mosquito larvae were collected. Emerged adults were assigned to mosquito species according to morphological analyses, followed by amplification and sequencing of genetic markers (COI, ND4, ITS2 and D2).

RESULTS

According to the morphological and genetic data, about 50 individuals belonged to the species Ae. koreicus.

CONCLUSION

We report the presence of Ae. koreicus in the district of Bergamo, which confirms the spread of this species in the north of Italy and raises concerns about its possible role as a vector of diseases in the Alpine area.

NS2B-NS3 protease inhibitors as promising compounds in the development of antivirals against Zika virus: A systematic review

Zika virus (ZIKV) infections are associated with severe neurological complications and are a global public health concern. There are no approved vaccines or antiviral drugs to inhibit ZIKV replication. NS2B-NS3 protease (NS2B-NS3 pro), which is essential for viral replication, is a promising molecular target for anti-ZIKV drugs. We conducted a systematic review to identify compounds with promising effects against ZIKV; we discussed their pharmacodynamic and pharmacophoric characteristics. The online search, performed using the PubMed/MEDLINE and SCOPUS databases, yielded 56 articles; seven relevant studies that reported nine promising compounds with inhibitory activity against ZIKV NS2B-NS3 pro were selected. Of these, five (niclosamide, nitazoxanide, bromocriptine, temoporfin, and novobiocin) are currently available on the market and have been tested for off-label use against ZIKV. The 50% inhibitory concentration values of these compounds for the inhibition of NS2B-NS3 pro ranged at 0.38-21.6 µM; most compounds exhibited noncompetitive inhibition (66%). All compounds that could inhibit the NS2B-NS3 pro complex showed potent in vitro anti-ZIKV activity with a 50% effective concentration ranging 0.024-50 µM. The 50% cytotoxic concentration of the compounds assayed using A549, Vero, and WRL-69 cell lines ranged at 0.6-1388.02 µM and the selectivity index was 3.07-1698. This review summarizes the most promising antiviral agents against ZIKV that have inhibitory activity against viral proteases.

Protective effect of house screening against indoor Aedes aegypti in Mérida, Mexico: A cluster randomised controlled trial

OBJECTIVE

To evaluate the protective effect of house screening (HS) on indoor Aedes aegypti infestation, abundance and arboviral infection in Merida, Mexico.

METHODS

In 2019, we performed a cluster randomised controlled trial (6 control and 6 intervention areas: 100 households/area). Intervention clusters received permanently fixed fiberglass HS on all windows and doors. The study included two cross-sectional entomologic surveys, one baseline (dry season in May 2019) and one post-intervention (PI, rainy season between September and October 2019). The presence and number of indoor Aedes females and blood-fed females (indoor mosquito infestation) as well as arboviral infections with dengue (DENV) and Zika (ZIKV) viruses were evaluated in a subsample of 30 houses within each cluster.

RESULTS

HS houses had significantly lower risk for having Aedes aegypti female mosquitoes (odds ratio [OR] = 0.56, 95% CI 0.33-0.97, p = 0.04) and blood-fed females (OR = 0.53, 95% CI 0.28-0.97, p = 0.04) than unscreened households from the control arm. Compared to control houses, HS houses had significantly lower indoor Ae. aegypti abundance (rate ratio [RR] = 0.50, 95% CI 0.30-0.83, p = 0.01), blood-fed Ae. aegypti females (RR = 0.48, 95% CI 0.27-0.85, p = 0.01) and female Ae. aegypti positive for arboviruses (OR = 0.29, 95% CI 0.10-0.86, p = 0.02). The estimated intervention efficacy in reducing Ae. aegypti arbovirus infection was 71%.

CONCLUSIONS

These results provide evidence supporting the use of HS as an effective pesticide-free method to control house infestations with Aedes aegypti and reduce the transmission of Aedes-transmitted viruses such as DENV, chikungunya (CHIKV) and ZIKV.

Insecticide resistance of Dengue vectors in South East Asia: a systematic review

BACKGROUND

The insecticides used widely has led to resistance in the vector and impose a challenge to vector control operation.

OBJECTIVES

This review aims to analyse the distribution of insecticide resistance of dengue vectors in South East Asia and to describe the mechanism of insecticide resistance.

METHODS

Literature search for articles published on 2015 to 2019 from PubMed, Scopus and ProQuest was performed. Total of 37 studies included in the final review from the initial 420 studies.

RESULTS

Pyrethroid resistance was concentrated on the west coast of Peninsular Malaysia and Northern Thailand and scattered at Java Island, Indonesia while organophosphate resistance was seen across the Java Island (Indonesia), West Sumatera and North Peninsular Malaysia. Organochlorine resistance was seen in Sabah, Malaysia and scattered distribution in Nusa Tenggara, Indonesia. V1016G, S989P, F1269C gene mutation in Aedes Aegypti were associated with Pyrethroid resistance in Singapore and Indonesia. In Malaysia, over-expressed with monooxygenase P450 genes (CYP9J27, CYP6CB1, CYP9J26 and CYP9M4) Glutathione S-transferases, carboxylesterases commonly associated with pyrethroids resistance in Aedes Aegypti and CYP612 overexpressed in Aedes Albopictus. The genetic mutation in A302S in Aedes Albopictus was associated with organochlorine resistance in Malaysia.

CONCLUSIONS

Rotation of insecticide, integration with synergist and routine assessment of resistance profile are recommended strategies in insecticide resistance management.

Insecticide resistance in Aedes aegypti from Tapachula, Mexico: Spatial variation and response to historical insecticide use

BACKGROUND

Insecticide use continues as the main strategy to control Aedes aegypti, the vector of dengue, Zika, chikungunya, and yellow fever. In the city of Tapachula, Mexico, mosquito control programs switched from pyrethroids to organophosphates for outdoor spatial spraying in 2013. Additionally, the spraying scheme switched from total coverage to focused control, prioritizing areas with higher entomological-virological risk. Five years after this strategy had been implemented, we evaluated the status and variability of insecticide resistance among Ae. aegypti collected at 26 sites in Tapachula.

METHODOLOGY/PRINCIPAL FINDINGS

We determined the lethal concentrations at 50% of the tested populations (LC50) using a bottle bioassay, and then, we calculated the resistance ratio (RR) relative to the susceptible New Orleans strain. Permethrin and deltamethrin (pyrethroids), chlorpyrifos and malathion (organophosphates), and bendiocarb (carbamate) were tested. The frequencies of the substitutions V1016I and F1534C, which are in the voltage-gated sodium channel and confer knockdown-resistance (kdr) to pyrethroid insecticides, were calculated. Despite 5 years having passed since the removal of pyrethroids from the control programs, Ae. aegypti remained highly resistant to permethrin and deltamethrin (RR > 10-fold). In addition, following 5 years of chlorpyrifos use, mosquitoes at 15 of 26 sites showed moderate resistance to chlorpyrifos (5- to 10-fold), and the mosquitoes from one site were highly resistant. All sites had low resistance to malathion (< 5-fold). Resistance to bendiocarb was low at 19 sites, moderate at five, and high at two. Frequencies of the V1016I ranged from 0.16-0.71, while C1534 approached fixation at 23 sites (0.8-1). Resistance profiles and kdr allele frequencies varied across Tapachula. The variability was not associated with a spatial pattern at the scale of the sampling.

CONCLUSION/SIGNIFICANCE

Mosquito populations respond to selection pressure at a focal scale in the field. Spatial variation across sites highlights the importance of testing multiple sites within geographical regions.

Detrimental effects of pyriproxyfen on the detoxification and abilities of Belostoma anurum to prey upon Aedes aegypti larvae

Despite being effective in controlling mosquito larvae and a few other target organisms, the application of insecticides into aquatic systems may cause unintended alterations to the physiology or behavioral responses of several aquatic non-target organisms, which can ultimately lead to their death. Here, we firstly evaluated whether the susceptibility of the giant water bug, Belostoma anurum (Hemiptera: Belostomatidae), a predator of mosquito larvae, to pyriproxyfen would be similar to that of its potential prey, larvae of Aedes aegypti (Diptera: Culicidae). Secondly, we recorded the nominal concentrations of pyriproxyfen in water and evaluated whether sublethal exposures would lead to physiological or behavioral alterations on the B. anurum nymphs. We characterized the activities of three major families of detoxification enzymes (i.e., cytochrome P450 monooxygenases, glutathione-S-transferase, and general esterases) and further evaluated the abilities of pyriproxyfen sublethally-exposed B. anurum to prey upon A. aegypti larvae at different prey densities. Our findings revealed that nominal pyriproxyfen concentration significantly decreased (approximately 50%) over the first 24 h. Furthermore, when applied at the concentration of 10 μg a.i./L, pyriproxyfen was approximately four times more toxic to A. aegypti larvae (LT₅₀ = 48 h) than to B. anurum nymphs (LT₅₀ = 192 h). Interestingly, the pyriproxyfen sublethally-exposed (2.5 μg a.i./L) B. anurum nymphs exhibited reduced enzyme activities (cytochrome P450 monooxygenases) involved in detoxication processes and preyed significantly less on A. aegypti larvae when compared to unexposed predators. Collectively, our findings demonstrate that mortality-based pyriproxyfen risk assessments are not always protective of aquatic non-target organisms.

Evaluation of a mosquito home system for controlling Aedes aegypti

BACKGROUND

Dengue is a significant public health issue that is caused by Aedes spp. mosquitoes. The current vector control methods are unable to effectively reduce Aedes populations and thus fail to decrease dengue transmission. Hence, there is an urgent need for new tools and strategies to reduce dengue transmission in a wide range of settings. In this study, the Mosquito Home System (MHS) and Mosquito Home Aqua (MHAQ) formulations were assessed as commercial autodissemination traps in laboratory and small-scale field trials.

METHOD

Multiple series of laboratory and small-scale field trials were performed to assess the efficacy of MHS and MHAQ exposed to Ae. aegypti. In the laboratory trials, various parameters such as fecundity, fertility, wing size, oviposition preferences, residual effects, and MHAQ transference to other containers through controlled experiments were tested. For small-scale field trials, the efficacy of the MHS and MHAQ approaches was determined to ascertain whether wild mosquitoes could transfer the MHAQ formulation from MHS stations to ovitraps.

RESULTS

The data revealed that Ae. aegypti was highly susceptible to low concentrations of MHAQ formulations and had a residual effect of up to 3 months, with MHAQ exposure affecting fecundity, fertility, and mosquito wing size. In the oviposition studies, gravid females strongly preferred the hay infusion compared to tap water and MHAQ during egg-laying in the laboratory. Nevertheless, the use of commercial MHAQ by MHS was highly attractive in field settings compared to conventional ovitraps among local Aedes spp. mosquitoes. In addition, MHAQ horizontal transfer activities in the laboratory and small-scale field trials were demonstrated through larval bioassays. These findings demonstrated the potential of MHAQ to be transferred to new containers in each study site.

CONCLUSION

This study provided proof of principle for the autodissemination of MHAQ. Through further refinement, this technique and device could become an effective oviposition trap and offer an alternative preventive tool for vector control management.

The economic costs of biological invasions in Central and South America: a first regional assessment

Invasive alien species are responsible for a high economic impact on many sectors worldwide. Nevertheless, there is a scarcity of studies assessing these impacts in Central and South America. Investigating costs of invasions is important to motivate and guide policy responses by increasing stakeholders’ awareness and identifying action priorities. Here, we used the InvaCost database to investigate (i) the geographical pattern of biological invasion costs across the region; (ii) the monetary expenditure across taxa and impacted sectors; and (iii) the taxa responsible for more than 50% of the costs (hyper-costly taxa) per impacted sector and type of costs. The total of reliable and observed costs reported for biological invasions in Central and South America was USD 102.5 billion between 1975 and 2020, but about 90% of the total costs were reported for only three countries (Brazil, Argentina and Colombia). Costs per species were associated with geographical regions (i.e., South America, Central America and Islands) and with the area of the countries in km2. Most of the expenses were associated with damage costs (97.8%), whereas multiple sectors (77.4%), agriculture (15%) and public and social welfare (4.2%) were the most impacted sectors. Aedes spp. was the hyper-costly taxon for the terrestrial environment (costs of USD 25 billion) and water hyacinth (Eichhornia crassipes) was the hyper-costly taxon for the aquatic environment (USD 179.9 million). Six taxa were classified as hyper-costly for at least one impacted sector and two taxa for at least one type of cost. In conclusion, invasive alien species caused billions of dollars of economic burden in Central and South America, mainly in large countries of South America. Costs caused by invasive alien species were unevenly distributed across countries, impacted sectors, types of costs and taxa (hyper-costly taxa). These results suggest that impacted sectors should drive efforts to manage the species that are draining financial sources.

Modelling the damage costs of invasive alien species

The rate of biological invasions is growing unprecedentedly, threatening ecological and socioeconomic systems worldwide. Quantitative understandings of invasion temporal trajectories are essential to discern current and future economic impacts of invaders, and then to inform future management strategies. Here, we examine the temporal trends of cumulative invasion costs by developing and testing a novel mathematical model with a population dynamical approach based on logistic growth. This model characterises temporal cost developments into four curve types (I–IV), each with distinct mathematical and qualitative properties, allowing for the parameterization of maximum cumulative costs, carrying capacities and growth rates. We test our model using damage cost data for eight genera (Rattus, Aedes, Canis, Oryctolagus, Sturnus, Ceratitis, Sus and Lymantria) extracted from the InvaCost database—which is the most up-to-date and comprehensive global compilation of economic cost estimates associated with invasive alien species. We find fundamental differences in the temporal dynamics of damage costs among genera, indicating they depend on invasion duration, species ecology and impacted sectors of economic activity. The fitted cost curves indicate a lack of broadscale support for saturation between invader density and impact, including for Canis, Oryctolagus and Lymantria, whereby costs continue to increase with no sign of saturation. For other taxa, predicted saturations may arise from data availability issues resulting from an underreporting of costs in many invaded regions. Overall, this population dynamical approach can produce cost trajectories for additional existing and emerging species, and can estimate the ecological parameters governing the linkage between population dynamics and cost dynamics.

Development and Validation of a Three-Dimensional Printed Multifunctional Trap for Surveillance of Mosquitoes

An essential component of vector-borne disease monitoring programs is mosquito surveillance. Surveillance efforts employ various collection traps depending on mosquito species and targeted life-history stage, i.e., eggs, larvae, host-seeking, resting, or gravid adults. Surveillance activities often use commercial traps, sometimes modified to accept specific mosquito species attractants. The advent of widely available and affordable 3D printing technology allows the construction of novel trap designs and components. The study goal was to develop and assess a cost-effective, multipurpose, 6-volt mosquito trap integrating features of both host-seeking and gravid mosquito traps to collect undamaged live specimens: a multifunctional mosquito trap (MMT). We tested the MMT in comparison to commercial traps, targeting gravid Aedes albopictus, host-seeking Ae. albopictus, and total number of host-seeking mosquitos regardless of species. Field evaluations found the MMT performed as well as or better than comparable commercial traps. This project demonstrates an easy to construct, inexpensive, and versatile mosquito trap, potentially useful for surveying multiple mosquito species and other hematophagous insects by varying attractants into the MMT.

Analyses of Insecticide Resistance Genes in Aedes aegypti and Aedes albopictus Mosquito Populations from Cameroon

The emergence of insecticide resistance in Aedes mosquitoes could pose major challenges for arboviral-borne disease control. In this paper, insecticide susceptibility level and resistance mechanisms were assessed in Aedes aegypti (Linnaeus, 1762) and Aedes albopictus (Skuse, 1894) from urban settings of Cameroon. The F1 progeny of Aedes aegypti and Aedes albopictus collected in Douala, Yaoundé and Dschang from August to December 2020 was tested using WHO tube assays with four insecticides: deltamethrin 0.05%, permethrin 0.75%, DDT 4% and bendiocarb 0.1%. TaqMan, qPCR and RT-qPCR assays were used to detect kdr mutations and the expression profiles of eight detoxification genes. Aedes aegypti mosquitoes from Douala were found to be resistant to DDT, permethrin and deltamethrin. Three kdr mutations, F1534C, V1016G and V1016I were detected in Aedes aegypti populations from Douala and Dschang. The kdr allele F1534C was predominant (90%) in Aedes aegypti and was detected for the first time in Aedes albopictus (2.08%). P450s genes, Cyp9J28 (2.23-7.03 folds), Cyp9M6 (1.49-2.59 folds), Cyp9J32 (1.29-3.75 folds) and GSTD4 (1.34-55.3 folds) were found overexpressed in the Douala and Yaoundé Aedes aegypti populations. The emergence of insecticide resistance in Aedes aegypti and Aedes albopictus calls for alternative strategies towards the control and prevention of arboviral vector-borne diseases in Cameroon.

Serological biomarker for assessing human exposure to Aedes mosquito bites during a randomized vector control intervention trial in northeastern Thailand

Background

Aedes mosquitoes are vectors for several major arboviruses of public health concern including dengue viruses. The relationships between Aedes infestation and disease transmission are complex wherein the epidemiological dynamics can be difficult to discern because of a lack of robust and sensitive indicators for predicting transmission risk. This study investigates the use of anti-Aedes saliva antibodies as a serological biomarker for Aedes mosquito bites to assess small scale variations in adult Aedes density and dengue virus (DENV) transmission risk in northeastern Thailand. Individual characteristics, behaviors/occupation and socio-demographics, climatic and epidemiological risk factors associated with human-mosquito exposure are also addressed.

Methods

The study was conducted within a randomized clustered control trial in Roi Et and Khon Kaen provinces over a consecutive 19 months period. Thirty-six (36) clusters were selected, each of ten houses. Serological and entomological surveys were conducted in all houses every four months and monthly in three sentinel households per cluster between September 2017 and April 2019 for blood spot collections and recording concurrent immature and adult Aedes indices. Additionally, the human exposure to Aedes mosquito bites (i.e., Mosquito Exposure Index or MEI) was estimated by ELISA measuring levels of human antibody response to the specific Nterm-34 kDa salivary antigen. The relationships between the MEI, vector infestation indices (adult and immature stages) and vector DENV infection were evaluated using a two-level (house and individual levels) mixed model analysis with one-month lag autoregressive correlation.

Results

There was a strong positive relationship between the MEI and adult Aedes (indoor and outdoor) density. Individuals from households with a medium mosquito density (mean difference: 0.091, p<0.001) and households with a high mosquito density (mean difference: 0.131, p<0.001) had higher MEI’s compared to individuals from households without Aedes. On a similar trend, individuals from households with a low, medium or high indoor Aedes densities (mean difference: 0.021, p<0.007, 0.053, p<0.0001 and 0.037, p<0.0001 for low, medium and high levels of infestation, respectively) had higher MEI than individuals from houses without indoor Aedes. The MEI was driven by individual characteristics, such as gender, age and occupation/behaviors, and varied according to climatic, seasonal factors and vector control intervention (p<0.05). Nevertheless, the study did not demonstrate a clear correlation between MEI and the presence of DENV-infected Aedes.

Conclusion

This study represents an important step toward the validation of the specific IgG response to the Aedes salivary peptide Nterm-34kDa as a proxy measure for Aedes infestation levels and human-mosquito exposure risk in a dengue endemic setting. The use of the IgG response to the Nterm-34 kDa peptide as a viable diagnostic tool for estimating dengue transmission requires further investigations and validation in other geographical and transmission settings.

Aedes mosquitoes and the viruses they transmit are major public health concerns for over half of the global human population. However, the quantitative relationships between virus transmission and vector mosquito infestation remain unclear despite numerous indicators used to estimate transmission risk and predict dengue outbreaks. The aim of this study is to investigate the use of a salivary biomarker to assess the small-scale variation in human exposure to Aedes bites and the risk of dengue infection in the context of a vector control intervention in northeastern Thailand. A cohort of 539 persons visited every four months, including 161 individuals visited monthly, were recruited for routine serological and concurrent household entomological surveys during 19 consecutive months follow-up. Antibody response to Aedes bites was measured by enzyme-linked immunosorbent assays to assess the mosquito exposure index (MEI) and association with the Aedes adult and immature abundance as well as the presence of dengue virus (DENV) in adult mosquitoes (transmission risk). Additionally, the individual (cohort), climatic, and vector control intervention risk factors associated with MEI are explored. This study demonstrates that the MEI was strongly related to household adult Aedes density, particularly indoors resting mosquitoes. Additionally, the MEI was influenced by individual characteristics (i.e., person age, gender, staying indoors), and varied according to seasons and intervention. Nonetheless, no clear relationship between MEI and dengue transmission risk (i.e., vector infection) was detected. This study demonstrated the potential usefulness of the MEI to assess heterogeneity in adult Aedes infestation indices that could assist public health authorities to rapidly identify mosquito “hot spots” and the timeliness of effective vector control interventions.

Management of insecticides for use in disease vector control: a global survey

Background

Vector control plays a critical role in the prevention, control and elimination of vector-borne diseases, and interventions of vector control continue to depend largely on the action of chemical insecticides. A global survey was conducted on the management practices of vector control insecticides at country level to identify gaps to inform future strategies on pesticide management, seeking to improve efficacy of interventions and reduce the side-effects of chemicals used on health and the environment.

Methods

A survey by questionnaire on the management practices of vector control insecticides was disseminated among all WHO Member States. Data were analysed using descriptive statistics in MS Excel.

Results

Responses were received from 94 countries, or a 48% response rate. Capacity for insecticide resistance monitoring was established in 68–80% of the countries in most regions, often with external support; however, this capacity was largely lacking from the European & Others Region (i.e. Western & Eastern Europe, North America, Australia and New Zealand). Procurement of vector control insecticides was in 50–75% of countries taking place by agencies other than the central-level procuring agency, over which the central authorities lacked control, for example, to select the product or assure its quality, highlighting the importance of post-market monitoring. Moreover, some countries experienced problems with estimating the correct amounts for procurement, especially for emergency purposes. Large fractions (29–78%) of countries across regions showed shortcomings in worker safety, pesticide storage practices and pesticide waste disposal. Shortcomings were most pronounced in countries of the European & Others Region, which has long been relatively free from mosquito-borne diseases but has recently faced challenges of re-emerging vector-borne diseases.

Conclusions

Critical shortcomings in the management of vector control insecticides are common in countries across regions, with risks of adverse pesticide effects on health and the environment. Advocacy and resource mobilization are needed at regional and country levels to address these challenges.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06155-y.

Management of insecticides for use in disease vector control: Lessons from six countries in Asia and the Middle East

Interventions to control the vectors of human diseases, notably malaria, leishmaniasis and dengue, have relied mainly on the action of chemical insecticides. However, concerns have been raised regarding the management of insecticides in vector-borne disease-endemic countries. Our study aimed to analyze how vector control insecticides are managed in selected countries to extract lessons learned.

A qualitative analysis of the situation of vector control insecticides management was conducted in six countries. Multi-stakeholder meetings and key informer interviews were conducted on aspects covering the pesticide lifecycle. Findings were compared and synthesized to extract lessons learned. Centrally executed guidelines and standards on the management of insecticides offered direction and control in most malaria programs, but were largely lacking from decentralized dengue programs, where practices of procurement, application, safety, storage, and disposal were variable between districts. Decentralized programs were better at facilitating participation of stakeholders and local communities and securing financing from local budgets. However, little coordination existed between malaria, visceral leishmaniasis and dengue programs within countries. Entomological capacity was concentrated in malaria programs at central level, while dengue and visceral leishmaniasis programs were missing out on expertise. Monitoring systems for insecticide resistance in malaria vectors were rarely used for dengue or visceral leishmaniasis vectors. Strategies for insecticide resistance management, where present, did not extend across programs or sectors in most countries. Dengue programs in most countries continued to rely on space spraying which, considering the realities on the ground, call for revision of international guidelines.

Vector control programs in the selected countries were confronted with critical shortcomings in the procurement, application, safety measures, storage, and disposal of vector control insecticides, with implications for the efficiency, effectiveness, and safety of vector control. Further international support is needed to assist countries in situation analysis, action planning and development of national guidelines on vector control insecticide management.

Vector-borne diseases such as dengue, malaria and leishmaniasis are transmitted by insect vectors. Transmission can be interrupted through vector control. Chemical insecticides are the mainstay for controlling these insect vectors. However, the use of chemicals also introduces risks to health and the environment and may lead to insecticide resistance. Hence, proper management of those insecticides is critical. To find out how the insecticides used for vector control are being managed, the authors conducted investigations in six countries in Asia and the Middle East. They found that the practices of insecticide procurement, application, storage, and disposal depended on how a program is organized. Dengue programs were operated in a decentralized manner and, consequently, lacked coordination through guidelines and standards on best practices. Also, coordination between malaria, visceral leishmaniasis and dengue programs within countries was minimal, and expertise needed to guide decisions on vector control and to monitor insecticide resistance was in short supply. The identified shortcomings in how vector control insecticides are managed likely affected the efficiency, effectiveness, and safety of vector control operations.

Widespread multiple insecticide resistance in the major dengue vector Aedes albopictus in Hainan Province, China

BACKGROUND

Aedes albopictus is a highly invasive mosquito and has become a potential vector of dengue, chikungunya and Zika viruses. Insecticide-based mosquito interventions are the main tools for vector-borne disease control. However, mosquito resistance to insecticides is a major threat to effective prevention and control. Five Ae. albopictus populations across Hainan Province, China were investigated for susceptibility to multiple insecticide and resistance mechanisms.

RESULTS

Larval bioassays indicated that resistance to pyrethroids was common in all larval populations. Adult bioassays revealed all populations were either resistant or highly resistant to at least four of the six synthetic insecticides (deltamethrin, permethrin, cyfluthrin, propoxur, malathion, and DDT) tested. Pre-exposure of mosquitoes to the synergistic agent piperonyl butoxide (PBO) increased mosquito mortality by 2.4-43.3% in bioassays to DDT, malathion, and permethrin and rendered mosquito sensitive to deltamethrin, cyfluthrin, and propoxur. The frequency of knockdown resistance (kdr) mutations (F1534S and F1534C) ranged from 69.8% to 89.3% and from 38.1% to 87.0% in field-resistant and sensitive populations, respectively. F1534S mutation was significantly associated with pyrethroid resistance. No mutation was detected in the acetylcholinesterase (ace-1) gene in the two examined populations.

CONCLUSION

This study provides evidence of widespread resistance to multiple insecticides in Ae. albopictus in Hainan Province, China. Both kdr mutations and metabolic detoxification were potential causes of insecticide resistance for Ae. albopictus. Our findings highlight the need for insecticide resistance management and mosquito control measures that do not entirely depend on synthetic insecticides. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A Case for Systematic Quality Management in Mosquito Control Programmes in Europe

The recent spread of invasive mosquito species, such as Aedes albopictus and the seasonal sporadic transmission of autochthonous cases of arboviral diseases (e.g., dengue, chikungunya, Zika) in temperate areas, such as Europe and North America, highlight the importance of effective mosquito-control interventions to reduce not only nuisance, but also major threats for public health. Local, regional, and even national mosquito control programs have been established in many countries and are executed on a seasonal basis by either public or private bodies. In order for these interventions to be worthwhile, funding authorities should ensure that mosquito control is (a) planned by competent scientific institutions addressing the local demands, (b) executed following the plan that is based on recommended and effective methods and strategies, (c) monitored regularly by checking the efficacy of the implemented actions, (d) evaluated against the set of targets, and (e) regularly improved according to the results of the monitoring. Adherence to these conditions can only be assured if a formal quality management system is adopted and enforced that ensures the transparency of effectiveness of the control operation. The current paper aims at defining the two components of this quality management system, quality assurance and quality control for mosquito control programs with special emphasis on Europe, but applicable over temperate areas.

Multisectoral Approach to Address Chikungunya Outbreaks Driven by Human Mobility: A Systematic Review and Meta-Analysis

BACKGROUND

The role of human mobility in the epidemiology of emerging Aedes-transmitted viral diseases is recognized but not fully understood. The objective of this systematic review and meta-analysis was to examine how human mobility patterns are driving chikungunya outbreaks.

METHODS

Literature was systematically reviewed for studies on chikungunya prevalence in countries/territories with high-level evidence of human mobility-driven outbreaks, based on: (1) emergence of chikungunya outbreaks with epidemic chikungunya virus genotypes among displaced/migrant populations and their hosting communities; and (2) identification of imported index case(s) with epidemic genotypes phylogenetically related to the genotypes circulating during emerging or subsequent outbreaks.

RESULTS

The meta-analysis of extracted prevalence data revealed that a large proportion of the population in countries/territories afflicted by outbreaks is still at risk of infection during future outbreaks. On the other hand, approximately one-half of suspected chikungunya cases could be infected with other co-circulating acute febrile illnesses.

CONCLUSIONS

We discussed in this paper how human mobility-driven chikungunya outbreaks can be addressed, and how the involvement of several sectors in addition to the health sector in multisectoral approaches (MSAs) is important for prevention and control of chikungunya and other Aedes-transmitted arboviral outbreaks.

Deep learning identification for citizen science surveillance of tiger mosquitoes

Global monitoring of disease vectors is undoubtedly becoming an urgent need as the human population rises and becomes increasingly mobile, international commercial exchanges increase, and climate change expands the habitats of many vector species. Traditional surveillance of mosquitoes, vectors of many diseases, relies on catches, which requires regular manual inspection and reporting, and dedicated personnel, making large-scale monitoring difficult and expensive. New approaches are solving the problem of scalability by relying on smartphones and the Internet to enable novel community-based and digital observatories, where people can upload pictures of mosquitoes whenever they encounter them. An example is the Mosquito Alert citizen science system, which includes a dedicated mobile phone app through which geotagged images are collected. This system provides a viable option for monitoring the spread of various mosquito species across the globe, although it is partly limited by the quality of the citizen scientists’ photos. To make the system useful for public health agencies, and to give feedback to the volunteering citizens, the submitted images are inspected and labeled by entomology experts. Although citizen-based data collection can greatly broaden disease-vector monitoring scales, manual inspection of each image is not an easily scalable option in the long run, and the system could be improved through automation. Based on Mosquito Alert’s curated database of expert-validated mosquito photos, we trained a deep learning model to find tiger mosquitoes (Aedes albopictus), a species that is responsible for spreading chikungunya, dengue, and Zika among other diseases. The highly accurate 0.96 area under the receiver operating characteristic curve score promises not only a helpful pre-selector for the expert validation process but also an automated classifier giving quick feedback to the app participants, which may help to keep them motivated. In the paper, we also explored the possibilities of using the model to improve future data collection quality as a feedback loop.

Sterile Insect Technique (SIT) against Aedes Species Mosquitoes: A Roadmap and Good Practice Framework for Designing, Implementing and Evaluating Pilot Field Trials

Aedes albopictus and Aedes aegypti are invasive mosquito species that impose a substantial risk to human health. To control the abundance and spread of these arboviral pathogen vectors, the sterile insect technique (SIT) is emerging as a powerful complement to most commonly-used approaches, in part, because this technique is ecologically benign, specific, and non-persistent in the environment if releases are stopped. Because SIT and other similar vector control strategies are becoming of increasing interest to many countries, we offer here a pragmatic and accessible 'roadmap' for the pre-pilot and pilot phases to guide any interested party. This will support stakeholders, non-specialist scientists, implementers, and decision-makers. Applying these concepts will ensure, given adequate resources, a sound basis for local field trialing and for developing experience with the technique in readiness for potential operational deployment. This synthesis is based on the available literature, in addition to the experience and current knowledge of the expert contributing authors in this field. We describe a typical path to successful pilot testing, with the four concurrent development streams of Laboratory, Field, Stakeholder Relations, and the Business and Compliance Case. We provide a graphic framework with criteria that must be met in order to proceed.

Piper capitarianum essential oil: a promising insecticidal agent for the management of Aedes aegypti and Aedes albopictus

Mosquitoes are responsible for serious public health problems worldwide, and as such, Aedes aegypti and Aedes albopictus are important vectors in the transmission of dengue, chikungunya, and Zika in Brazil and other countries of the world. Due to growing resistance to chemical insecticides among populations of vectors, environmentally friendly strategies for vector management are receiving ever more attention. Essential oils (EOs) extracted from plants have activities against insects with multiple mechanisms of action. These mechanisms hinder the development of resistance, and have the advantages of being less toxicity and biodegradable. Thus, the present study aimed to evaluate the chemical composition of the EOs obtained from Piper capitarianum Yunck, as well as evaluating their insecticidal potential against Aedes aegypti and A. albopictus, and their toxicity in relation to Artemia salina. The yields of the EOs extracted from the leaves, stems, and inflorescences of P. capitarianum were 1.2%, 0.9%, and 0.6%, respectively, and their main constituents were trans-caryophyllene (20.0%), α-humulene (10.2%), β-myrcene (10.5%), α-selinene (7.2%), and linalool (6.0%). The EO from the inflorescences was the most active against A. aegypti and A. albopictus, and exhibited the respective larvicidal (LC₅₀ = 87.6 μg/mL and 76.1 μg/mL) and adulticide activities (LC₅₀ = 126.2 μg/mL and 124.5 μg/mL). This EO was also the most active in the inhibition of AChE, since it presented an IC₅₀ value of 14.2 μg/mL. Its larvicidal effect was observed under optical and scanning electron microscopy. Additionally, non-toxic effects against A. salina were observed. Docking modeling of trans-caryophyllene and α-humulene on sterol carrier protein-2 (SCP-2) suggests that both molecules have affinity with the active site of the enzyme, which indicates a possible mechanism of action. Therefore, the essential oil of P. capitarianum may be used in the development of new insecticide targets for the control of A. aegypti and A. albopictus in the Amazonian environment.

A long-lasting biological larvicide against the dengue vector mosquito Aedes albopictus

BACKGROUND

Aedes albopictus is the primary vector of mosquito-borne diseases, including dengue and chikungunya, in China. The management of vector mosquitoes is the primary strategy for the control of such infectious diseases. The gravid Ae. albopictus prefers to skip-oviposit its eggs into different small water containers, and the management of these breeding places is critical for mosquito control. Bacillus thuringiensis subspecies Israelensis (Bti) is a useful biological larvicide, but the effective period of the currently available commercial product is relatively short. This study aimed to develop a long-lasting formulation of Bti to control the dengue vector mosquito Ae. albopictus.

RESULTS

Water-soluble polyethylene glycols and water-insoluble hexadecanol were mixed with Bti to develop the long-lasting formulation Bti-BLOCK, based on the solid dispersion technique. The controlled release of Bti-BLOCK and its effect on Ae. albopictus were assayed in the laboratory and in the field. The results showed that Bti toxins were slowly released from Bti-BLOCK into the water and maintained at an effective dose for at least 6 months. Bti-BLOCK caused high mortality during the immature stage (>90%) and achieved full inhibition during pupation (100%). The efficacy lasted at least 12 weeks in the laboratory and 6 weeks in the field. Furthermore, we confirmed an 89% reduction in Ae. albopictus density and a reduction in the R₀ of dengue to a low-risk level after 6 months of open-field interventions.

CONCLUSIONS

We developed a long-lasting biological larvicide, Bti-BLOCK, which displayed very good efficacy in the control of the dengue vector mosquito Ae. albopictus.

Insecticide-treated house screening protects against Zika-infected Aedes aegypti in Merida, Mexico

Background

The integration of house-screening and long-lasting insecticidal nets, known as insecticide-treated screening (ITS), can provide simple, safe, and low-tech Aedes aegypti control. Cluster randomised controlled trials in two endemic localities for Ae. aegypti of south Mexico, showed that ITS conferred both, immediate and sustained (~2 yr) impact on indoor-female Ae. aegypti infestations. Such encouraging results require further validation with studies quantifying more epidemiologically-related endpoints, including arbovirus infection in Ae. aegypti. We evaluated the efficacy of protecting houses with ITS on Ae. aegypti infestation and arbovirus infection during a Zika outbreak in Merida, Yucatan, Mexico.

Methodology/Principal findings

A two-arm cluster-randomised controlled trial evaluated the entomological efficacy of ITS compared to the absence of ITS (with both arms able to receive routine arbovirus vector control) in the neighbourhood Juan Pablo II of Merida. Cross-sectional entomological surveys quantified indoor adult mosquito infestation and arbovirus infection at baseline (pre-ITS installation) and throughout two post-intervention (PI) surveys spaced at 6-month intervals corresponding to dry/rainy seasons over one year (2016–2017). Household-surveys assessed the social reception of the intervention. Houses with ITS were 79–85% less infested with Aedes females than control houses up to one-year PI. A similar significant trend was observed for blood-fed Ae. aegypti females (76–82%). Houses with ITS had significantly less infected female Ae. aegypti than controls during the peak of the epidemic (OR = 0.15, 95%CI: 0.08–0.29), an effect that was significant up to a year PI (OR = 0.24, 0.15–0.39). Communities strongly accepted the intervention, due to its perceived mode of action, the prevalent risk for Aedes-borne diseases in the area, and the positive feedback from neighbours receiving ITS.

Conclusions/Significance

We show evidence of the protective efficacy of ITS against an arboviral disease of major relevance, and discuss the relevance of our findings for intervention adoption.

We evaluated the efficacy of protecting houses with insecticide-treated nets permanently fixed with aluminium frames on external doors and windows on Ae. aegypti infestation and arbovirus infection during a Zika outbreak in Merida, Yucatan, Mexico. Houses protected with screens were ≈80% less infested with Aedes females and very importantly, had significantly less infected female Ae. aegypti during the peak of the epidemic. Communities strongly accepted the intervention, due to its perceived mode of action, the prevalent risk for Aedes-borne diseases in the area, and the positive feedback from neighbours. House screening provides a simple, affordable sustainable method to reduce human-vector contact inside houses and can protect against dengue, chikungunya and Zika.

Long Non-Coding RNAs and Their Potential Roles in the Vector-Host-Pathogen Triad

Long non-coding (lnc)RNAs have emerged as critical regulators of gene expression and are involved in almost every cellular process. They can bind to other molecules including DNA, proteins, or even other RNA types such messenger RNA or small RNAs. LncRNAs are typically expressed at much lower levels than mRNA, and their expression is often restricted to tissue- or time-specific developmental stages. They are also involved in several inter-species interactions, including vector–host–pathogen interactions, where they can be either vector/host-derived or encoded by pathogens. In these interactions, they function via multiple mechanisms including regulating pathogen growth and replication or via cell-autonomous antimicrobial defense mechanisms. Recent advances suggest that characterizing lncRNAs and their targets in different species may hold the key to understanding the role of this class of non-coding RNA in interspecies crosstalk. In this review, we present a general overview of recent studies related to lncRNA-related regulation of gene expression as well as their possible involvement in regulating vector–host–pathogen interactions.

A Review: Aedes-Borne Arboviral Infections, Controls and Wolbachia-Based Strategies

Arthropod-borne viruses (Arboviruses) continue to generate significant health and economic burdens for people living in endemic regions. Of these viruses, some of the most important (e.g., dengue, Zika, chikungunya, and yellow fever virus), are transmitted mainly by Aedes mosquitoes. Over the years, viral infection control has targeted vector population reduction and inhibition of arboviral replication and transmission. This control includes the vector control methods which are classified into chemical, environmental, and biological methods. Some of these control methods may be largely experimental (both field and laboratory investigations) or widely practised. Perceptively, one of the biological methods of vector control, in particular, Wolbachia-based control, shows a promising control strategy for eradicating Aedes-borne arboviruses. This can either be through the artificial introduction of Wolbachia, a naturally present bacterium that impedes viral growth in mosquitoes into heterologous Aedes aegypti mosquito vectors (vectors that are not natural hosts of Wolbachia) thereby limiting arboviral transmission or via Aedes albopictus mosquitoes, which naturally harbour Wolbachia infection. These strategies are potentially undermined by the tendency of mosquitoes to lose Wolbachia infection in unfavourable weather conditions (e.g., high temperature) and the inhibitory competitive dynamics among co-circulating Wolbachia strains. The main objective of this review was to critically appraise published articles on vector control strategies and specifically highlight the use of Wolbachia-based control to suppress vector population growth or disrupt viral transmission. We retrieved studies on the control strategies for arboviral transmissions via arthropod vectors and discussed the use of Wolbachia control strategies for eradicating arboviral diseases to identify literature gaps that will be instrumental in developing models to estimate the impact of these control strategies and, in essence, the use of different Wolbachia strains and features.

Biological and Chemical Control of Mosquito Population by Optimal Control Approach

This paper focuses on the design and analysis of short-term control intervention measures seeking to suppress local populations of Aedes aegypti mosquitoes, the major transmitters of dengue and other vector-borne infections. Besides traditional measures involving the spraying of larvicides and/or insecticides, we include biological control based on the deliberate introduction of predacious species feeding on the aquatic stages of mosquitoes. From the methodological standpoint, our study relies on application of the optimal control modeling framework in combination with the cost-effectiveness analysis. This approach not only enables the design of optimal strategies for external control intervention but also allows for assessment of their performance in terms of the cost-benefit relationship. By examining numerous scenarios derived from combinations of chemical and biological control measures, we try to find out whether the presence of predacious species at the mosquito breeding sites may (partially) replace the common practices of larvicide/insecticide spraying and thus reduce their negative impact on non-target organisms. As a result, we identify two strategies exhibiting the best metrics of cost-effectiveness and provide some useful insights for their possible implementation in practical settings.

Knowledge on exotic mosquitoes in Germany, and public acceptance and effectiveness of Bti and two self-prepared insecticides against Aedes japonicus japonicus

Mosquito-borne diseases are a continuous challenge to public health. To prevent transmission, Integrated Vector Management (IVM) applies preventive, control, and communicational strategies that should be feasible, environmentally benign, and sustainable. IVM shows higher efficiency when being supported by local communities. Accordingly, we applied a social-ecological approach to identify the public acceptance of control measures and effectiveness of Eurocent coins containing copper, clove essential oil (EO) and Bacillus thuringiensis israelensis (Bti). We performed field and laboratory experiments to demonstrate the toxicity of alternative substances against Aedes japonicus japonicus. In expert interviews, we asked for (1) knowledge on exotic mosquitoes in Germany, (2) potential chances of alternative substances in future mosquito control, and (3) their needs for further clarification before application. We assessed potential users' (4) awareness of exotic mosquitoes and (5) willingness to apply the substances. Self-prepared copper coins and EO were clearly preferred by potential users over Bti. However, 100% mortality of the sensitive first stage could not be reached with the number of ten 5-Eurocent coins showing limited toxicity. Clove EO was shown to work as oviposition deterrent and larvicide with a LC50 of 17 mg l-1 (95% CI: 15-19 mg l-1). This study shows the importance of potential users' perspectives in IVM and the need for authorised insecticides.

The Antiviral Small-Interfering RNA Pathway Induces Zika Virus Resistance in Transgenic Aedes aegypti

The resurgence of arbovirus outbreaks across the globe, including the recent Zika virus (ZIKV) epidemic in 2015–2016, emphasizes the need for innovative vector control methods. In this study, we investigated ZIKV susceptibility to transgenic Aedes aegypti engineered to target the virus by means of the antiviral small-interfering RNA (siRNA) pathway. The robustness of antiviral effector expression in transgenic mosquitoes is strongly influenced by the genomic insertion locus and transgene copy number; we therefore used CRISPR/Cas9 to re-target a previously characterized locus (Chr2:321382225) and engineered mosquitoes expressing an inverted repeat (IR) dsRNA against the NS3/4A region of the ZIKV genome. Small RNA analysis revealed that the IR effector triggered the mosquito’s siRNA antiviral pathway in bloodfed females. Nearly complete (90%) inhibition of ZIKV replication was found in vivo in both midguts and carcasses at 7 or 14 days post-infection (dpi). Furthermore, significantly fewer transgenic mosquitoes contained ZIKV in their salivary glands (p = 0.001), which led to a reduction in the number of ZIKV-containing saliva samples as measured by transmission assay. Our work shows that Ae. aegypti innate immunity can be co-opted to engineer mosquitoes resistant to ZIKV.

ZanzaMapp: A Scalable Citizen Science Tool to Monitor Perception of Mosquito Abundance and Nuisance in Italy and Beyond

Mosquitoes represent a considerable nuisance and are actual/potential vectors of human diseases in Europe. Costly and labour-intensive entomological monitoring is needed to correct planning of interventions aimed at reducing nuisance and the risk of pathogen transmission. The widespread availability of mobile phones and of massive Internet connections opens the way to the contribution of citizen in complementing entomological monitoring. ZanzaMapp is the first mobile “mosquito” application for smartphones specifically designed to assess citizens’ perception of mosquito abundance and nuisance in Italy. Differently from other applications targeting mosquitoes, ZanzaMapp prioritizes the number of records over their scientific authentication by requesting users to answer four simple questions on perceived mosquito presence/abundance/nuisance and geo-localizing the records. The paper analyses 36,867 ZanzaMapp records sent by 13,669 devices from 2016 to 2018 and discusses the results with reference to either citizens’ exploitation and appreciation of the app and to the consistency of the results obtained with the known biology of main mosquito species in Italy. In addition, we provide a first small-scale validation of ZanzaMapp data as predictors of Aedes albopictus biting females and examples of spatial analyses and maps which could be exploited by public institutions and administrations involved in mosquito and mosquito-borne pathogen monitoring and control.

Assessment of the susceptibility status of Aedes aegypti (Diptera: Culicidae) populations to pyriproxyfen and malathion in a nation-wide monitoring of insecticide resistance performed in Brazil from 2017 to 2018

BACKGROUND

Chemical mosquito control using malathion has been applied in Brazil since 1985. To obtain chemical control effectiveness, vector susceptibility insecticide monitoring is required. This study aimed to describe bioassay standardizations and determine the susceptibility profile of Ae. aegypti populations to malathion and pyriproxyfen, used on a national scale in Brazil between 2017 and 2018, and discuss the observed impacts in arbovirus control.

METHODS

The diagnostic-doses (DD) of pyriproxyfen and malathion were determined as the double of adult emergence inhibition (EI) and lethal doses for 99% of the Rockefeller reference strain, respectively. To monitor natural populations, sampling was performed in 132 Brazilian cities, using egg traps. Colonies were raised in the laboratory for one or two generations (F1 or F2) and submitted to susceptibility tests, where larvae were exposed to the pyriproxyfen DD (0.03 µg/l) and adults, to the malathion DD determined in the present study (20 µg), in addition to the one established by the World Health Organization (WHO) DD (50 µg) in a bottle assay. Dose-response (DR) bioassays with pyriproxyfen were performed on populations that did not achieve 98% EI in the DD assays.

RESULTS

Susceptibility alterations to pyriproxyfen were recorded in six (4.5%) Ae. aegypti populations from the states of Bahia and Ceará, with Resistance Ratios (RR95) ranging from 1.51 to 3.58. Concerning malathion, 73 (55.3%) populations distributed throughout the country were resistant when exposed to the local DD 20 µg/bottle. On the other hand, no population was resistant, and only 10 (7.6%) populations in eight states were considered as exhibiting decreased susceptibility (mortality ratios between 90 and 98%) when exposed to the WHO DD (50 µg/bottle).

CONCLUSIONS

The feasibility of conducting an insecticide resistance monitoring action on a nation-wide scale was confirmed herein, employing standardized and strongly coordinated sampling methods and laboratory bioassays. Brazilian Ae. aegypti populations exhibiting decreased susceptibility to pyriproxyfen were identified. The local DD for malathion was more sensitive than the WHO DD for early decreased susceptibility detection.

The COVID-19 pandemic should not jeopardize dengue control

The concurrent circulation of dengue and coronavirus disease 2019 (COVID-19) may produce many unfavourable outcomes—such as co-infections; delays in diagnosis, treatment, and mitigation measures; overwhelming of the healthcare system; underreporting of cases; deterioration in surveillance and control interventions; and exacerbation of social inequalities. Indeed, lockdown is greatly compromising the effectiveness of vector control, especially social mobilization campaigns and preventive insecticide spraying in private spaces (indoor and peridomestic spraying). Thus, failure to appropriately implement the full range of vector control interventions can lead to a reduction in their overall effectiveness and an increasing risk of vector-borne diseases circulating. Consequently, the health community and policy makers should develop proactive policies and allocate adequate resources to prevent and manage the resurgence of dengue and other vector-borne diseases in the new era of COVID-19.

Managing disease outbreaks: The importance of vector mobility and spatially heterogeneous control

Management strategies for control of vector-borne diseases, for example Zika or dengue, include using larvicide and/or adulticide, either through large-scale application by truck or plane or through door-to-door efforts that require obtaining permission to access private property and spray yards. The efficacy of the latter strategy is highly dependent on the compliance of local residents. Here we develop a model for vector-borne disease transmission between mosquitoes and humans in a neighborhood setting, considering a network of houses connected via nearest-neighbor mosquito movement. We incorporate large-scale application of adulticide via aerial spraying through a uniform increase in vector death rates in all sites, and door-to-door application of larval source reduction and adulticide through a decrease in vector emergence rates and an increase in vector death rates in compliant sites only, where control efficacies are directly connected to real-world experimentally measurable control parameters, application frequencies, and control costs. To develop mechanistic insight into the influence of vector motion and compliance clustering on disease controllability, we determine the basic reproduction number R0 for the system, provide analytic results for the extreme cases of no mosquito movement, infinite hopping rates, and utilize degenerate perturbation theory for the case of slow but non-zero hopping rates. We then determine the application frequencies required for each strategy (alone and combined) in order to reduce R0 to unity, along with the associated costs. Cost-optimal strategies are found to depend strongly on mosquito hopping rates, levels of door-to-door compliance, and spatial clustering of compliant houses, and can include aerial spray alone, door-to-door treatment alone, or a combination of both. The optimization scheme developed here provides a flexible tool for disease management planners which translates modeling results into actionable control advice adaptable to system-specific details.

Using spatial genetics to quantify mosquito dispersal for control programs

Background

Hundreds of millions of people get a mosquito-borne disease every year and nearly one million die. Transmission of these infections is primarily tackled through the control of mosquito vectors. The accurate quantification of mosquito dispersal is critical for the design and optimization of vector control programs, yet the measurement of dispersal using traditional mark-release-recapture (MRR) methods is logistically challenging and often unrepresentative of an insect’s true behavior. Using Aedes aegypti (a major arboviral vector) as a model and two study sites in Singapore, we show how mosquito dispersal can be characterized by the spatial analyses of genetic relatedness among individuals sampled over a short time span without interruption of their natural behaviors.

Results

Using simple oviposition traps, we captured adult female Ae. aegypti across high-rise apartment blocks and genotyped them using genome-wide SNP markers. We developed a methodology that produces a dispersal kernel for distance which results from one generation of successful breeding (effective dispersal), using the distance separating full siblings and 2nd- and 3rd-degree relatives (close kin). The estimated dispersal distance kernel was exponential (Laplacian), with a mean dispersal distance (and dispersal kernel spread σ) of 45.2 m (95% CI 39.7–51.3 m), and 10% probability of a dispersal > 100 m (95% CI 92–117 m). Our genetically derived estimates matched the parametrized dispersal kernels from previous MRR experiments. If few close kin are captured, a conventional genetic isolation-by-distance analysis can be used, as it can produce σ estimates congruent with the close-kin method if effective population density is accurately estimated. Genetic patch size, estimated by spatial autocorrelation analysis, reflects the spatial extent of the dispersal kernel “tail” that influences, for example, the critical radii of release zones and the speed of Wolbachia spread in mosquito replacement programs.

Conclusions

We demonstrate that spatial genetics can provide a robust characterization of mosquito dispersal. With the decreasing cost of next-generation sequencing, the production of spatial genetic data is increasingly accessible. Given the challenges of conventional MRR methods, and the importance of quantified dispersal in operational vector control decisions, we recommend genetic-based dispersal characterization as the more desirable means of parameterization.

Botanical insecticide-based nanosystems for the control of Aedes (Stegomyia) aegypti larvae

Aedes (Stegomyia) aegypti is a cosmopolitan species that transmits arbovirus of medical importance as dengue, Zika, and chikungunya. The main strategy employed for the control of this mosquito is the use of larvicidal agents. However, the overuse of synthetic chemical larvicides has led to an increase in resistant insects, making management difficult. Therefore, the use of botanical insecticide-based nanosystems as an alternative to the use of synthetic agents for the control of Ae. aegypti has gained more considerable attention in the last years, mainly due to the advantages of nanostructured delivery systems, such as (a) controlled release; (b) greater surface area; (c) improvement of biological activity; (d) protection of natural bioactive agents from the environment and thus achieving stability; and (e) lipophilic drugs are easier dispersed even in aqueous vehicles. This review summarizes the current knowledge about botanical insecticide-based nanosystems as larvicidal against Ae. aegypti larvae. The majority of papers used metallic nanoparticles (NPs) as larvicidal agents, mainly silver nanoparticles (AgNPs), showing potential for their use as an alternative, followed by nanoemulsions containing vegetable oils, most essential oils, nanosystems that allow the dispersion of this high hydrophobic product in water, the environment of larval development. The final section describes scientific findings about the mode of action of these NPs, showing the gap about this subject in literature.

Semi-field evaluation of freestanding transfluthrin passive emanators and the BG sentinel trap as a "push-pull control strategy" against Aedes aegypti mosquitoes

Background

Spatial repellents that drive mosquitoes away from treated areas, and odour-baited traps, that attract and kill mosquitoes, can be combined and work synergistically in a push-pull system. Push-pull systems have been shown to reduce house entry and outdoor biting rates of malaria vectors and so have the potential to control other outdoor biting mosquitoes such as Aedes aegypti that transmit arboviral diseases. In this study, semi-field experiments were conducted to evaluate whether a push-pull system could be used to reduce bites from Aedes mosquitoes.

Methods

The push and pull under investigation consisted of two freestanding transfluthrin passive emanators (FTPE) and a BG sentinel trap (BGS) respectively. The FTPE contained hessian strips treated with 5.25 g of transfluthrin active ingredient. The efficacies of FTPE and BGS alone and in combination were evaluated by human landing catch in a large semi-field system in Tanzania. We also investigated the protection of FTPE over six months. The data were analyzed using generalized linear mixed models with binomial distribution.

Results

Two FTPE had a protective efficacy (PE) of 61.2% (95% confidence interval (CI): 52.2–69.9%) against the human landing of Ae. aegypti. The BGS did not significantly reduce mosquito landings; the PE was 2.1% (95% CI: −2.9–7.2%). The push-pull provided a PE of 64.5% (95% CI: 59.1–69.9%). However, there was no significant difference in the PE between the push-pull and the two FTPE against Ae. aegypti (P = 0.30). The FTPE offered significant protection against Ae. aegypti at month three, with a PE of 46.4% (95% CI: 41.1–51.8%), but not at six months with a PE of 2.2% (95% CI: −9.0–14.0%).

Conclusions

The PE of the FTPE and the full push-pull are similar, indicative that bite prevention is primarily due to the activity of the FTPE. While these results are encouraging for the FTPE, further work is needed for a push-pull system to be recommended for Ae. aegypti control. The three-month protection against Ae. aegypti bites suggests that FTPE would be a useful additional control tool during dengue outbreaks, that does not require regular user compliance.

Proliferation of Aedes aegypti in urban environments mediated by the availability of key aquatic habitats

Aedes aegypti is the main vector of dengue, Zika, chikungunya, and yellow fever viruses. Controlling populations of vector mosquito species in urban environments is a major challenge and being able to determine what aquatic habitats should be prioritized for controlling Ae. aegypti populations is key to the development of more effective mosquito control strategies. Therefore, our objective was to leverage on the Miami-Dade County, Florida immature mosquito surveillance system based on requested by citizen complaints through 311 calls to determine what are the most important aquatic habitats in the proliferation of Ae. aegypti in Miami. We used a tobit model for Ae. aegypti larvae and pupae count data, type and count of aquatic habitats, and daily rainfall. Our results revealed that storm drains had 45% lower percentage of Ae. aegypti larvae over the total of larvae and pupae adjusted for daily rainfall when compared to tires, followed by bromeliads with 33% and garbage cans with 17%. These results are indicating that storm drains, bromeliads and garbage cans had significantly more pupae in relation to larvae when compared to tires, traditionally know as productive aquatic habitats for Ae. aegypti. Ultimately, the methodology and results from this study can be used by mosquito control agencies to identify habitats that should be prioritized in mosquito management and control actions, as well as to guide and improve policies and increase community awareness and engagement. Moreover, by targeting the most productive aquatic habitats this approach will allow the development of critical emergency outbreak responses by directing the control response efforts to the most productive aquatic habitats.

Efficacy and Spatial Extent of Yard-Scale Control of Aedes (Stegomyia) albopictus (Diptera: Culicidae) Using Barrier Sprays and Larval Habitat Management

The Asian tiger mosquito, Aedes (Stegomyia) albopictus (Skuse), is a peridomestic, container-ovipositing mosquito commonly found throughout the southeastern United States. In the United States, Ae. albopictus is typically considered a nuisance pest; however, it is capable of transmitting multiple pathogens. Ae. albopictus is an important pest species and the target of numerous mosquito control efforts in the United States. Here, we evaluate the effectiveness and spatial extent of Ae. albopictus population reduction using a bifenthrin (AI Bifen IT, 7.9%) barrier spray and larval habitat management (LHM) in a temperate, suburban setting. Sixteen pairs of adjoining neighbors were randomly assigned to treatment groups with one neighbor receiving a treatment and the other monitored for evidence of a spillover effect of the treatments. Ae. albopictus populations in both yards were monitored for 33 d, with treatments occurring on the eighth day. Barrier sprays, both alone and combined with LHM, resulted in a significant reduction in Ae. albopictus abundance posttreatment. While LHM alone did not result in a significant reduction over the entire posttreatment period, Ae. albopictus populations were observed to be in decline during this period. No treatments were observed to have any reduction in efficacy 25 d posttreatment, with treatments involving LHM having a significantly increased efficacy. Yards neighboring treated yards were also observed to have reduced population sizes posttreatment, but these differences were rarely significant. These results provide insights into the population dynamics of Ae. albopictus following two common treatments and will be useful for integrated pest management plans.

Susceptibility of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) to Temephos in Thailand and Surrounding Countries

Aedes-borne virus disease control relies on insecticides to interrupt transmission. Temephos remains a key chemical for control of immature stage Aedes in Thailand and much of Southeast Asia. However, repeated use of insecticides may result in selection for resistance in vector populations, thus compromising operational intervention. Herein, the phenotypic response to temephos by Aedes aegypti (L.) and Aedes albopictus (Skuse) collected in Thailand and surrounding countries is presented. Data from 345 collection sites are included: 283 from literature review (244 sites with Ae. aegypti, 21 with Ae. albopictus, and 18 having both species sampled), plus 62 locations with Ae. aegypti in Thailand conducted between 2014 and 2018. Susceptibility assays followed WHO guidelines using the recommended discriminating dose of temephos (0.012 mg/liter) against late third to early fourth instar Ae. aegypti. Findings revealed 34 locations with susceptible Ae. aegypti, 13 with suspected resistance, and 15 indicating resistance. Published data between 1999 and 2019 in Thailand found Ae. aegypti resistant in 73 of 206 collection sites, whereas 3 locations from 11 sampled with low-level resistant in Ae. albopictus. From surrounding countries conducting temephos assays (Cambodia, Lao PDR, Myanmar, Malaysia, and Singapore), resistance is present in Ae. aegypti and Ae. albopictus from 27 of 56 and 19 of 28 locations, respectively. Routine insecticide susceptibility monitoring should be an operational requirement in vector control programs. Given the wide distribution and apparent increase in temephos-resistance, alternative larvicidal compounds must be considered if chemical control is to remain a viable vector control strategy.