Truck-Mounted Area-Wide Application of Pyriproxyfen Targeting Aedes aegypti and Aedes albopictus in Northeast Florida

Assessment of Truck-Mounted Area-Wide S-methoprene Applications to Manage West Nile Virus Vector Species in the Suburbs of Chicago, IL, USA

West Nile virus remains the leading cause of arboviral neuroinvasive disease in the United States, despite extensive efforts to control the mosquito vectors involved in transmission. In this study, we evaluated the effectiveness of Altosid SR-20 (active ingredient, S-methoprene 20%) larvicide applications using truck-mounted ultra-low volume (ULV) dispersal equipment to target Culex pipiens Linnaeus (Diptera: Culicidae) and Cx. restuans (Theobald)larvae. A combination of emergence bioassays, open-field measurements of deposited S-methoprene and spray distribution using gas chromatography-mass spectrometry, and assessments of adult Culex spp. populations in response to applications were conducted over the summer of 2020 within the North Shore Mosquito Abatement District (IL, USA). Open-field applications revealed that dispersed Altosid SR-20 using ULV equipment was effective (75% emergence inhibition in susceptible lab strain Cx. pipiens larvae) up to 53 m. In suburban neighborhood applications, we found that S-methoprene deposition and larval emergence inhibition (EI) in front yards did not differ significantly from backyards. An overall EI of 46% and 28% were observed for laboratory strain Cx. pipiens and wild Cx. restuans larvae respectively, and both had an EI significantly higher than the untreated control group. The EI of exposed wild Cx. pipiens larvae did not differ from the untreated controls, suggesting an increased tolerance to S-methoprene. No difference in abundance of gravid or host-seeking adult Culex spp. post-application was detected between treated and untreated sites. These results document the ability of area-wide application to distribute S-methoprene, but this strategy will need further modifications and evaluation for Culex spp. management.

Effectiveness of a Buffalo Turbine and A1 Mist Sprayer for the Areawide Deployment of Larvicide for Mosquito Control in an Urban Residential Setting

The control of medically important container-inhabiting mosquitoes is an ongoing challenge for mosquito control operations. Truck-mounted application equipment is a common option for rapid areawide larvicide deployment utilized by mosquito control operations. We tested the effectiveness of two truck-mounted sprayers (A1 Super Duty + Buffalo Turbine CSM3), for the deployment of water-dispersible biopesticides (VectoBac WDG:VectoLex WDG 50:50). Sixty residences within four residential neighborhoods in New Jersey were treated in 2019 and 2020. Three empty bioassay cups were placed in specific locations on each property (front yard/ back yard/ side of house), with an additional cup placed in an adjacent catch basin. This approach was replicated in two untreated control neighborhoods. Following larvicide application, cups were subjected to bioassays wherein larval mortality was tracked through adult eclosion. Overall, average larval mortality rates were 56% higher in treated cups compared against untreated controls. Mortality rates were affected by cup location, with 39% mortality in bioassay cups from back yards, 54% in those from the sides of houses, 73% in front yards, and 76% from cups in catch basins. Mortality did not differ significantly between the four treated neighborhoods, nor by the type of sprayer used. Our research shows that truck-mounted sprayers can be an effective method for larvicide deployment in residential neighborhoods, but effectiveness may depend upon the location of the target treatment area in relation to residences and other geographic obstacles.

Statewide Efficacy Assessment of Insect Growth Regulators Against Aedes albopictus (Diptera: Culicidae) in Sabah, Malaysia: An Alternative Control Strategy?

The efficacy of three groups of insect growth regulators, namely juvenile hormone mimics (methoprene and pyriproxyfen), chitin synthesis inhibitors (diflubenzuron and novaluron), and molting disruptor (cyromazine) was evaluated for the first time, against Aedes albopictus Skuse (Diptera: Culicidae) larvae from 14 districts in Sabah, Malaysia. The results showed that all field populations of Ae. albopictus were susceptible towards methoprene, pyriproxyfen, diflubenzuron, novaluron, and cyromazine, with resistance ratio values ranging from 0.50-0.90, 0.60-1.00, 0.67-1.17, 0.71-1.29, and 0.74-1.07, respectively. Overall, the efficacy assessment of insect growth regulators in this study showed promising outcomes and they could be further explored as an alternative to conventional insecticides.

Use of High-Performance Liquid Chromatography-Mass Spectrometry of Adipose Tissue for Detection of Bioaccumulation of Pyriproxyfen in Adults of Lithobates catesbeianus

The aims of the study were: (i) evaluate the efficacy of using amphibian adipose tissue as a valid biomarker of water contaminated by pyriproxyfen; and (ii) verify the use of Lithobates catesbeianus in laboratory experiments as a potential bioindicator for bioaccumulation of pesticide in adipose tissue from amphibians. Adult frogs were exposed to different dilutions (0.002 g/L and 0.02 g/L) of Sumilarv® (pyriproxyfen) over 50 days. The average results of the fortified sample were 108%, indicating that the test method was effective. Adult frogs exposed to the standard dose recommended by the World Health Organization (WHO) showed bioaccumulation of pyriproxyfen in adipose tissue significantly higher than control animals. Lithobates catesbeianus proved to be an effective bioindicator and the adipose tissue was an efficient biomarker to bioaccumulation of pyriproxyfen. We conclude that high-performance liquid chromatography-mass spectrometry was effective measuring pyriproxyfen bioaccumulation in adult amphibians.

A Review of the Control of Aedes aegypti (Diptera: Culicidae) in the Continental United States

Aedes aegypti (L) is an anthropophilic mosquito involved in the transmission of a variety of viral pathogens worldwide including dengue, chikungunya, yellow fever, and Zika viruses. This species, native to Africa, is well established in the continental U.S. (CONUS) and occasionally contributes to localized outbreaks of viral diseases. In the last seven decades, mosquito control programs in the CONUS have been focused on vectors of eastern equine encephalitis, St. Louis encephalitis, and West Nile viruses, as well as nuisance species. Aedes aegypti receives little control focus except during outbreak periods, which has led to a lack of information on appropriate and effective control options targeting Ae. aegypti in the CONUS. As such, in the event of an Ae. aegypti-borne arboviral outbreak in the CONUS, there are limited evidence-based control recommendations or protocols in place. Autochthonous outbreaks of Ae. aegypti-borne pathogens have occurred recently in the CONUS, including dengue outbreaks in 2010 and 2013, a chikungunya outbreak in 2014, and the 2016 outbreak of Zika virus. The increasing frequency of Ae. aegypti-borne outbreaks necessitates increased attention and research on control of this species to prevent and mitigate future outbreaks. This review consolidates and synthesizes the available literature on control of Ae. aegypti, specifically within the CONUS, focusing on data generated through operational applications as well as field and semifield experiments. The purpose of this review is to identify and highlight areas where additional research is needed. The review covers chemical control and insecticide resistance, biological control, source reduction, trapping, and alternative techniques.

Use of pyriproxyfen in control of Aedes mosquitoes: A systematic review

Dengue is the most rapidly spreading arboviral disease in the world. The current lack of fully protective vaccines and clinical therapeutics creates an urgent need to identify more effective means of controlling Aedes mosquitos, principally Aedes aegypti, as the main vector of dengue. Pyriproxyfen (PPF) is an increasingly used hormone analogue that prevents juvenile Aedes mosquitoes from becoming adults and being incapable of transmitting dengue. The objectives of the review were to (1) Determine the effect of PPF on endpoints including percentage inhibition of emergence to adulthood, larval mortality, and resistance ratios; and (2) Determine the different uses, strengths, and limitations of PPF in control of Aedes. A systematic search was applied to Pubmed, EMBASE, Web of Science, LILACS, Global Health, and the Cochrane database of Systematic Reviews. Out of 1,369 records, 90 studies met the inclusion criteria. Nearly all fit in one of the following four categories 1) Efficacy of granules, 2) Auto-dissemination/horizontal transfer, 3) use of ultra-low volume thermal fogging (ULV), thermal fogging (TF), or fumigant technologies, and 4) assessing mosquito resistance. PPF granules had consistently efficacious results of 90-100% inhibition of emergence for up to 90 days. The evidence is less robust but promising regarding PPF dust for auto-dissemination and the use of PPF in ULV, TF and fumigants. Several studies also found that while mosquito populations were still susceptible to PPF, the lethal concentrations increased among temephos-resistant mosquitoes compared to reference strains. The evidence is strong that PPF does increase immature mortality and adult inhibition in settings represented in the included studies, however future research should focus on areas where there is less evidence (e.g. auto-dissemination, sprays) and new use cases for PPF. A better understanding of the biological mechanisms of cross-resistance between PPF, temephos, and other insecticides will allow control programs to make better informed decisions.

Using UPLC-MS/MS to Evaluate the Dissemination of Pyriproxyfen by Aedes Mosquitoes to Combat Cryptic Larval Habitats after Source Reduction in Kaohsiung in Southern Taiwan

The policy regarding mosquito control strategies in Taiwan is based on integrated vector management (IVM). The major approach is source reduction via collaboration by both residents and governments. However, small and cryptic habitats of dengue vectors are hard to find and eliminate in urban communities. Therefore, this study evaluated a complementary approach that targeted cryptic habitats by utilizing mosquitoes themselves as vehicles to transfer an insect growth regulator, pyriproxyfen (PPF), to their breeding sites; the amount of PPF in breeding water was determined with ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC–MS/MS). A bioassay conducted by introducing ten late-instar larvae into PPF solution was performed to assess emergence inhibition (EI). PPF was found at 0.56 ± 0.04 ng in 25 mL of water by dissemination via ten Aedes aegypti mosquitoes exposed to 0.01% PPF, leading to 100% EI. After the community-level source reduction, a field trial in Kaohsiung in Southern Taiwan showed that 30.8–31.5% of cryptic ovitraps reached EI ≥ 50% one month after spraying 0.01% PPF in microhabitats favored by mosquitoes. IVM in parallel with residual spraying of PPF on resting surfaces of mosquitoes could serve as a simple and complementary approach to reduce cryptic larval sources in urban communities in Southern Taiwan.

Timing of Lambda-Cyhalothrin and Pyriproxyfen Barrier Treatments for Aedes albopictus (Diptera: Culicidae) Management

Barrier applications, treating vegetation and other potential mosquito resting areas with residual pesticides, have become standard practice for commercial pest management professionals offering mosquito control services. These treatments are generally effective in reducing numbers of the Asian tiger mosquito, Aedes albopictus (Skuse). In the temperate climates, adult Ae. albopictus populations are naturally eliminated each winter and must be grown from diapausing eggs the following spring. Therefore, early-season control interventions timed before populations rebound may further reduce population growth compared with interventions that take place after the population has peaked. We compared Early (1 June) barrier applications of lambda-cyhalothrin (Demand CS) mixed with the insect growth regulator pyriproxyfen (Archer IGR) to Late applications (31 July) in urban and suburban residential parcels in New Jersey. These applications resulted in 43 and 51% reductions in adult Ae. albopictus populations in the Early and Late intervention study parcels, respectively, when compared with the untreated Controls. Indirect applications of pyriproxyfen (i.e., rainwater runoff transferring pesticide) to potential larval habitat did not cause mortality in laboratory larval bioassays but direct mist applications of the Archer and Demand combination to larval habitats led to elevated larval mortality over a 6-wk period. The Early-season intervention offered no advantage in efficacy on adult populations compared with the Late-season intervention, which targeted peak mosquito populations. Our study provides support for the efficacy of barrier applications and illustrates the importance of timing barrier treatments to coincide with established Ae. albopictus action thresholds.

Truck-mounted area-wide applications of larvicides and adulticides for extended suppression of adult Aedes albopictus

BACKGROUND

Given the lack of vaccines for most vector-borne diseases, vector control is often the primary option for disease control. Aedes albopictus are difficult to control because the immatures primarily develop in containers ubiquitous in residential properties. Conventional adulticide campaigns often result in brief, rebounding population declines, so incorporating new techniques into an integrated pest management program is imperative. We performed combined area-wide applications of the larvicides Bacillus thuringiensis var. israelensis and pyriproxyfen with the adulticide sumithrin and prallethrin to achieve extended suppression of Ae. albopictus populations in Trenton, NJ, USA. We deployed bioassay cups to assess the spatial penetration and efficacy of the applications.

RESULTS

Inhibition of adult emergence was significantly higher in the treatment bioassay cups than in laboratory controls (z = 4.65, P < 0.0001) and field control bioassay cups (z = 8.93, P < 0.0001). We observed a lower trend in adult numbers following season-long combined application of pyriproxyfen and adulticide, with numbers of adult Ae. albopictus at the treatment site up to five times lower than at the control site.

CONCLUSION

Pyriproxyfen is a powerful mosquito larvicide and pupacide with low mammalian toxicity that shows promise for area-wide vehicle-mounted (either ground or airborne) applications. © 2018 Society of Chemical Industry.

Evaluation of Lambda-Cyhalothrin and Pyriproxyfen Barrier Treatments for Aedes albopictus (Diptera: Culicidae) Management in Urbanized Areas of New Jersey

Mosquito control programs in the United States are still searching for best management practices to control the Asian tiger mosquito, Aedes albopictus (Skuse; Diptera: Culicidae). Most intervention methods for this species are either labor intensive (e.g., source reduction) or short-term (e.g., ultra-low-volume adulticiding). We investigated the effectiveness of barrier spray pesticide applications within urban and suburban residential yards in New Jersey as a control strategy using a before-after-control-impact (BACI) approach. Applications of Demand CSR pyrethroid (9.7% AI lambda-cyhalothrin) only or combined Demand CSR and Archer IGR insect growth regulator (1.3% AI pyriproxyfen) applications resulted in significant and similar decreases in adult mosquito abundance post-treatment ranging from 78 to 74% respectively, compared with the untreated control. Both insecticides exceeded the 70% reduction threshold considered as effective for Ae. albopictus control for 2 to 4 wk. However, applications of Archer IGR alone did not reduce adult mosquito abundance. The field study results were supported by laboratory no-choice bioassays using treated leaf foliage. Our study is the first data driven evidence of the residual efficacy of barrier pesticide applications in New Jersey with lambda-cyhalothrin that provided significant reductions in adult Ae. albopictus populations for an extended duration.

Laboratory Evaluation of a Novel Lethal Ovitrap for Control of Aedes aegypti

Aedes aegypti (L.) (Diptera: Culicidae) are known to flourish in a variety of natural and residential habitats and are competent vectors of at least 22 different arboviruses, including dengue, chikungunya, and Zika. Their global distribution, anthropophilic nature, and vector competency make them species of interest for control. A novel durable dual-action lethal ovitrap (DDALO) with combined larviciding and adulticiding effects, as well as a slow-release polymer (isobutyl methacrylate), was designed to target Ae. aegypti. The use of the DDALO resulted in high adult mosquito mortality (~95-100%) in no-choice laboratory cage studies targeting gravid females and successfully prevented all deposited eggs from hatching. Aging of the traps caused some loss in activity over time, but they still caused adult mortality (~50%) and continued to prevent successful hatching of eggs for 6 mo. Oviposition preference studies resulted in ~4.5 times as many larvae developing in untreated DDALOs compared with the other containers combined. Small-cage multigenerational studies resulted in significantly lower populations of adult mosquitoes in cages containing treated DDALOs after 4 wk. Successful laboratory studies show that the DDALO appears to be a promising tool that could be used for controlling wild vector populations of Ae. aegypti in combination with other mosquito control practices.

Community effectiveness of pyriproxyfen as a dengue vector control method: A systematic review

Background

Vector control is the only widely utilised method for primary prevention and control of dengue. The use of pyriproxyfen may be promising, and autodissemination approach may reach hard to reach breeding places. It offers a unique mode of action (juvenile hormone mimic) and as an additional tool for the management of insecticide resistance among Aedes vectors. However, evidence of efficacy and community effectiveness (CE) remains limited.

Objective

The aim of this systematic review is to compile and analyse the existing literature for evidence on the CE of pyriproxyfen as a vector control method for reducing Ae. aegypti and Ae. albopictus populations and thereby human dengue transmission.

Methods

Systematic search of PubMed, Embase, Lilacs, Cochrane library, WHOLIS, Web of Science, Google Scholar as well as reference lists of all identified studies. Removal of duplicates, screening of abstracts and assessment for eligibility of the remaining studies followed. Relevant data were extracted, and a quality assessment conducted. Results were classified into four main categories of how pyriproxyfen was applied: - 1) container treatment, 2) fumigation, 3) auto-dissemination or 4) combination treatments,–and analysed with a view to their public health implication.

Results

Out of 745 studies 17 studies were identified that fulfilled all eligibility criteria. The results show that pyriproxyfen can be effective in reducing the numbers of Aedes spp. immatures with different methods of application when targeting their main breeding sites. However, the combination of pyriproxyfen with a second product increases efficacy and/or persistence of the intervention and may also slow down the development of insecticide resistance. Open questions concern concentration and frequency of application in the various treatments. Area-wide ultra-low volume treatment with pyriproxyfen currently lacks evidence and cannot be recommended. Community participation and acceptance has not consistently been successful and needs to be further assessed. While all studies measured entomological endpoints, only two studies measured the reduction in human dengue cases, with inconclusive results.

Conclusions

Although pyriproxyfen is highly effective in controlling the immature stages of dengue transmitting mosquitoes, and–to a smaller degree–adult mosquitoes, there is weak evidence for a reduction of human dengue cases. More well designed larger studies with appropriate standardised outcome measures are needed before pyriproxyfen is incorporated in routine vector control programmes. Additionally, resistance to pyriproxyfen has been reported and needs investigation.

There is evidence that pyriproxyfen may effectively reduce the density of immature mosquito stages when applied to identified breeding sites. Various formulations are commercially available, and easy to use without a health threat to the user. However, questions remain regarding its use as a single agent in a community setting. Considering its mode of action, it would not be the product of choice for use in an acute outbreak setting. However, for a sustainable community approach, especially slow-release pyriproxyfen formulations seem promising, because they are the longest lasting choice. The analysis suggests, that combination with a second vector control chemical, preferably an adulticide tackling different stages of mosquito development, increases the efficacy of pyriproxyfen and prolongs the duration of a single application. This systematic literature review clearly shows that there is a need for further studies, preferably utilising cluster-randomised controlled (cRCT) designs, to investigate the community effectiveness of pyriproxyfen and to link entomological outcomes to human dengue transmission.

Disruptive technology for vector control: the Innovative Vector Control Consortium and the US Military join forces to explore transformative insecticide application technology for mosquito control programmes

Malaria vector control technology has remained largely static for decades and there is a pressing need for innovative control tools and methodology to radically improve the quality and efficiency of current vector control practices. This report summarizes a workshop jointly organized by the Innovative Vector Control Consortium (IVCC) and the Armed Forces Pest Management Board (AFPMB) focused on public health pesticide application technology. Three main topics were discussed: the limitations with current tools and techniques used for indoor residual spraying (IRS), technology innovation to improve efficacy of IRS programmes, and truly disruptive application technology beyond IRS. The group identified several opportunities to improve application technology to include: insuring all IRS programmes are using constant flow valves and erosion resistant tips; introducing compression sprayer improvements that help minimize pesticide waste and human error; and moving beyond IRS by embracing the potential for new larval source management techniques and next generation technology such as unmanned “smart” spray systems. The meeting served to lay the foundation for broader collaboration between the IVCC and AFPMB and partners in industry, the World Health Organization, the Bill and Melinda Gates Foundation and others.