State-wide survey of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) in Florida

Evaluation of a novel triple-action adulticide containing a pyrethroid, macrocyclic lactone, and fatty acid against pyrethroid-resistant Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Insecticide resistance in mosquito populations has long been recognized as a significant global public health challenge, motivating the development of new control chemistries. ReMoa Tri is a novel triple-action space spray that employs a different mode of action than traditional adult mosquito control formulations. It combines 3 components: fenpropathrin, a mixed-type I/II pyrethroid; abamectin, a macrocyclic lactone; and C8910, a patented fatty acid chain. As an ultra-low volume adulticide, ReMoa Tri has the potential to target mosquito species that are resistant to pyrethroid and organophosphate-based control materials. To determine whether ReMoa Tri effectively targets resistant mosquito species in Florida's Collier County, United States, we conducted ground-based field cage trials using field-caught pyrethroid-resistant Culex quinquefasciatus (Say) and Aedes aegypti (L.), of which the latter also displayed developing resistance to organophosphates. Trials were also conducted against the same mosquito populations with Merus 3.0, a pyrethrin-based adulticide used by the Collier Mosquito Control District. ReMoa Tri was effective against Collier's pyrethroid-resistant Cx. quinquefasciatus, resulting in more than 95% mortality in semifield cage trials by 24 h postapplication. Similarly, ReMoa Tri applications against Collier's pyrethroid-resistant Ae. aegypti resulted in 72%-89% mortality at 24 h postapplication and 74%-97% mortality at 48 h postapplication. This study represents the first field data on this novel space spray, and its findings shed light on the performance of ReMoa Tri against local mosquito populations that have developed resistance to currently available adulticides.

Insecticide resistance of Miami-Dade Culex quinquefasciatus populations and initial field efficacy of a new resistance-breaking adulticide formulation

Sporadic outbreaks of human cases of West Nile virus (WNV), primarily vectored by Culex quinquefasciatus Say in suburban and urban areas, have been reported since introduction of the virus into Florida in 2001. Miami-Dade County, Florida is part of one of the largest metropolitan areas in the United States, supports Cx. quinquefasciatus year-round, and recently experienced over 60 human cases of WNV during one outbreak. To facilitate more effective integrated vector management and public health protection, we used the Centers for Disease Control and Prevention (CDC) bottle bioassay method to evaluate the susceptibility of adult Cx. quinquefasciatus collected from 29 locations throughout Miami-Dade County to pyrethroid and organophosphate adulticide active ingredients (AIs) used by Miami-Dade County Mosquito Control. We also determined the frequency of the 1014 knockdown resistance (kdr) mutation for Cx. quinquefasciatus from a subset of 17 locations. We detected resistance to two pyrethroid AIs in all tested locations (permethrin: 27 locations, deltamethrin: 28 locations). The 1014F allele was widely distributed throughout all 17 locations sampled; however, 29.4% of these locations lacked 1014F homozygotes even though phenotypic pyrethroid resistance was present. Organophosphate resistance was more variable; 20.7% of the locations tested were susceptible to malathion, and 33.3% of the populations were susceptible to naled. We subsequently conducted a field trial of ReMoa Tri, a recently approved multiple AI adulticide formulation labelled for resistant mosquitoes, against a mixed location field population of Miami-Dade Cx. quinquefasciatus. Average 24-hr mortality was 65.1 ± 7.2% and 48-hr mortality increased to 85.3 ± 9.1%, indicating good control of these resistant Cx. quinquefasciatus. This current study shows that insecticide resistance is common in local Cx. quinquefasciatus but effective options are available to maintain control during active disease transmission in Miami-Dade County.

Introduction and Spread of Dengue Virus 3, Florida, USA, May 2022-April 2023

During May 2022-April 2023, dengue virus serotype 3 was identified among 601 travel-associated and 61 locally acquired dengue cases in Florida, USA. All 203 sequenced genomes belonged to the same genotype III lineage and revealed potential transmission chains in which most locally acquired cases occurred shortly after introduction, with little sustained transmission.

Voltage-gated ion channels are expressed in the Malpighian tubules and anal papillae of the yellow fever mosquito (Aedes aegypti), and may regulate ion transport during salt and water imbalance

Vectors of infectious disease include several species of Aedes mosquitoes. The life cycle of Aedes aegypti, the yellow fever mosquito, consists of a terrestrial adult and an aquatic larval life stage. Developing in coastal waters can expose larvae to fluctuating salinity, causing salt and water imbalance, which is addressed by two prime osmoregulatory organs - the Malpighian tubules (MTs) and anal papillae (AP). Voltage-gated ion channels (VGICs) have recently been implicated in the regulation of ion transport in the osmoregulatory epithelia of insects. In the current study, we: (i) generated MT transcriptomes of freshwater-acclimated and brackish water-exposed larvae of Ae. aegypti, (ii) detected expression of several voltage-gated Ca2+, K+, Na+ and non-ion-selective ion channels in the MTs and AP using transcriptomics, PCR and gel electrophoresis, (iii) demonstrated that mRNA abundance of many altered significantly following brackish water exposure, and (iv) immunolocalized CaV1, NALCN, TRP/Painless and KCNH8 in the MTs and AP of larvae using custom-made antibodies. We found CaV1 to be expressed in the apical membrane of MTs of both larvae and adults, and its inhibition to alter membrane potentials of this osmoregulatory epithelium. Our data demonstrate that multiple VGICs are expressed in osmoregulatory epithelia of Ae. aegypti and may play an important role in the autonomous regulation of ion transport.

Resistance and inhibitor testing on Aedes aegypti (Linnaeus) (Culicidae: Diptera) populations in the Florida Keys

Aedes aegypti is the species of greatest concern for mosquito-borne disease in the Florida Keys. Previous locally transmitted dengue outbreaks in Key West (2009-2010) and Key Largo (2020) illustrate the need for an immediate and effective response plan to maintain Ae. aegypti populations below threshold levels. An important part of the Florida Keys Mosquito Control District's vector response plan is adulticide application because it can provide an immediate reduction in Ae. aegypti adults in the community. It has become apparent that in the Florida Keys, and throughout Florida, Ae. aegypti resistance to the adulticide permethrin is prevalent. This study uses the CDC bottle bioassay method to look at resistance in Ae. aegypti collected from Key Largo, Vaca Key, and Key West, FL. Resistance was found in all three populations when exposed to permethrin and Sumithrin® but not malathion. Inhibitor testing revealed that esterase and glutathione transferase activity is involved in resistance to permethrin in Key Largo and Key West Ae. aegypti populations while oxidase activity is involved in resistance to permethrin in Ae. aegypti from Vaca Key. Lack of knockdown at the diagnostic time and previous studies detecting the presence of kdr-associated allele mutations suggest knockdown resistance in all three populations. Results from this study show that there are multiple factors involved with resistance in the Ae. aegypti populations in the Florida Keys and that resistance mechanisms vary between islands. Continued surveillance will remain important so the most effective active ingredients can be used in response to future disease transmission.

Insecticide resistance: Status and potential mechanisms in Aedes aegypti

Aedes aegypti, an important vector in the transmission of human diseases, has developed resistance to two commonly used classes of insecticides, pyrethroids and organophosphates, in populations worldwide. This study examined sensitivity/resistance to chlorpyrifos, fenitrothion, malathion, deltamethrin, permethrin, and β-cyfluthrin, along with possible metabolic detoxification and target site insensitivity, in three Aedes aegypti mosquito strains. The resistant strain (PR) had developed high levels of resistance to all three pyrethroid insecticides compared to a susceptible population, with 6, 500-, 3200- and 17,000-fold resistance to permethrin, β-cyfluthrin, and deltamethrin, respectively. A newly emerged Ae. aegypti population collected from St. Augustine, Florida (AeStA) showed elevated levels of resistance to malathion (12-fold) and permethrin (25-fold). Synergists DEF (S,S,S,-tributyl phosphorotrithioate) and DEM (diethyl maleate) showed no or minor effects on insecticide resistance in both the AeStA and PRG20strains, but PBO (piperonyl butoxide) completely abolished resistance to both malathion and permethrin in AeStA and partially suppressed resistance in PR. The voltage-gated sodium channel sequences were examined to explore the mechanism that only partially inhibited the suppression of resistance to PBO in PR. Two mutations, V1016G/I and F1534C substitutions, both of which are associated with the development of pyrethroid resistance, were identified in the PRG20 strain but not in AeStA. These results suggest that while cytochrome P450 mediated detoxification may not be solely responsible, it is the major mechanism governing the development of resistance in AeStA. Both P450 mediated detoxification and target site insensitivity through the mutations in the voltage-gated sodium channel contribute to the high levels of resistance in the PRG20 strain.

Consumption of endemic arbovirus mosquito vectors by bats in the southeastern United States

Mosquitoes affect human health and well-being globally through their roles as disease-causing pathogen vectors. Utilizing genetic techniques, we conducted a large-scale dietary study of three bat species common to the southeastern U.S.A., Lasiurus seminolus (Seminole bat), Nycticeius humeralis (evening bat), and Myotis austroriparius (southeastern myotis). Through next-generation sequencing of a 180 bp portion of cytochrome oxidase subunit I (COI) of mitochondrial DNA from 180 bat guano samples, we documented consumption of 17 species of mosquitoes by bats, including six endemic arbovirus vectors. Culex quinquefasciatus, Culex coronator, Culiseta melanura, Culex salinarius, Culex erraticus, and Coquillettidia perturbans were consumed by 51.3%, 43.7%, 27.2%, 22.8%, 18.0%, and 12.7% of bats sampled, respectively. Consumption of two of these mosquito species was explained by spatial variables reflecting the prevalence of mosquito larval habitat, five were explained by bat traits (bat mass, bat species), and two were explained by these factors plus temporal variables (maximum daily temperature, time since sunset, date), making it challenging to offer specific guidance on how best to promote bats as a means of reducing arbovirus vector species. Our results show that common bat species of the southeastern U.S.A. consume endemic, but not exotic, arbovirus mosquito vectors. Future studies are needed to understand the impact of bat consumption on mosquito numbers and public health.

Past, present and future distribution of the yellow fever mosquito Aedes aegypti: The European paradox

The global distribution of the yellow fever mosquito Aedes aegypti is the subject of considerable attention because of its pivotal role as a biological vector of several high profile disease pathogens including dengue, chikungunya, yellow fever, and Zika viruses. There is also a lot of interest in the projected future species' distribution. However, less effort has been focused on its historical distribution, which has changed substantially over the past 100 years, especially in southern Europe where it was once widespread, but largely disappeared by the middle of the 20th century. The present work utilises all available historical records of the distribution of Ae. aegypti in southern Europe, the Near East within the Mediterranean Basin and North Africa from the late 19th century until the 1960's to construct a spatial distribution model using matching historical climatic and demographic data. The resulting model was then implemented using current climate and demographic data to assess the potential distribution of the vector in the present. The models were rerun with several different assumptions about the thresholds that determine habitat suitability for Ae. aegypti. The historical model matches the historical distributions well. When it is run with current climate values, the predicted present day distribution is somewhat broader than it used to be particularly in north-west France, North Africa and Turkey. Though it is beginning to reappear in the eastern Caucasus, this 'potential' distribution clearly does not match the actual distribution of the species, which suggests some other factors are responsible for its absence. Future distributions based on the historical model also do not match future distributions derived from models based only on present day vector distributions, which predict little or no presence in the Mediterranean Region. At the same time, the vector is widespread in the USA which is predicted to consolidate its range there in future. This contradiction and the implication for possible re-invasion of Europe are discussed.

Impacts of differential mosquito control treatment regimens on insecticide susceptibility status of Aedes aegypti (Diptera: Culicidae)

Abstract

Aedes aegypti (Linnaeus) is an invasive mosquito species and notable vector of several pathogens in the USA. Their cryptic and anthropophilic nature puts this species in close association with humans, where they can also be a nuisance. Mosquito control programs are the front line of defense for protecting the community from nuisance-biting and disease. However, the occurrence and prevalence of insecticide resistance in mosquitoes is a well-documented phenomenon that directly impacts the efficacy of insecticide applications. In Florida specifically, widespread resistance in Ae. aegypti has created a need for operational strategies that combat and, ideally, reverse resistance. Laboratory studies and the association between fitness costs and insecticide resistance indicate that this reversion is possible under the right conditions. For a 2.5-year period, the impact of varying operational treatment regimens on insecticide resistance in Ae. aegypti is evaluated using kdr genotyping and the CDC bottle bioassay. In an organophosphate treatment area, a decrease in frequency of a double homozygous resistant genotype was observed. CDC bottle bioassays did not reveal any clear trends in the data to indicate a reversion to insecticide susceptibility. However, the changes in genotype could indicate the first step back to insecticide susceptibility. This study provides preliminary data that has implications for resistance management in mosquito control operations.

Article Highlights

The Invasive Mosquitoes of Canada: An Entomological, Medical, and Veterinary Review

Several invasive mosquitoes have become established in Canada, including important pathogen vectors such as Aedes albopictus, Ae. japonicus, and Culex pipiens. Some species have been present for decades, while others are recent arrivals. Several species present new health concerns and may result in autochthonous seasonal outbreaks of pathogens, particularly in southern Canada, that were previously restricted to imported cases. This review provides an overview of current knowledge of the biological, medical, and veterinary perspectives of these invasive species and highlights the need for increased monitoring efforts and information sharing.

Needs Assessment of Southeastern United States Vector Control Agencies: Capacity Improvement Is Greatly Needed to Prevent the Next Vector-Borne Disease Outbreak

A national 2017 vector control capacity survey was conducted to assess the United States’ (U.S.’s) ability to prevent emerging vector-borne disease. Since that survey, the southeastern U.S. has experienced continued autochthonous exotic vector-borne disease transmission and establishment of invasive vector species. To understand the current gaps in control programs and establish a baseline to evaluate future vector control efforts for this vulnerable region, a focused needs assessment survey was conducted in early 2020. The southeastern U.S. region was targeted, as this region has a high probability of novel vector-borne disease introduction. Paper copies delivered in handwritten envelopes and electronic copies of the survey were delivered to 386 unique contacts, and 150 returned surveys were received, corresponding to a 39% response rate. Overall, the survey found vector control programs serving areas with over 100,000 residents and those affiliated with public health departments had more core capabilities compared to smaller programs and those not affiliated with public health departments. Furthermore, the majority of vector control programs in this region do not routinely monitor for pesticide resistance. Taken as a whole, these results suggest that the majority of the southeastern U.S. is vulnerable to vector-borne disease outbreaks. Results from this survey raise attention to the critical need of providing increased resources to bring all vector control programs to a competent level, ensuring that public health is protected from the threat of vector-borne disease.

Experimental evaluation of a metofluthrin passive emanator against Aedes albopictus

Background

With the recent occurrence of locally transmitted Aedes-borne viruses in the continental United States and Europe, and a lack of effective vaccines, new approaches to control Aedes aegypti and Aedes albopictus are needed. In sub-tropical urban settings in the US, Ae. albopictus is a dominant nuisance and arbovirus vector species. Unfortunately, the vector control toolbox against Ae. albopictus is not as well developed as for Ae. aegypti. Here, we evaluate the efficacy, longevity, and range of protectiveness of a novel passive metofluthrin emanator (10% active ingredient in a polyethylene mesh) against Ae. albopictus indoors and outdoors.

Methods

Four studies were conducted comparing the presence of the metofluthrin emanator to a control lacking emanator with interest in quantifying efficacy by human landing counts. Studies evaluated the effect of an emanator at varying distances from one or more human volunteers indoors and outdoors. Efficacy of emanators over time since activation was also evaluated.

Results

Mixed-effects models determined that sitting in close proximity to an emanator reduced landings by 89.5% outdoors and by 74.6% indoors. The emanator was determined protective when located immediately next to a human volunteer outdoors but not uniformly protective when located further away. The emanator was protective at all tested distances from the device indoors. Mortality of mosquitoes exposed to metofluthrin emanators was ~2x higher than those who were not exposed in indoor conditions. Finally, a Generalized Additive Model determined that emanators used continuously outdoors lost their effect after 2.5 weeks and stopped inducing paralysis in mosquitoes after 3.8 weeks of use.

Conclusions

We show strong and lasting efficacy of 10% metofluthrin emanators against field Ae. albopictus both in indoor and outdoor conditions. Metofluthrin emanators can protect people from Ae. albopictus bites, representing a viable option for reducing human-mosquito contacts at home and beyond.

Reproductive interference and Satyrisation: mechanisms, outcomes and potential use for insect control

Reproductive Interference occurs when interactions between individuals from different species disrupt reproductive processes, resulting in a fitness cost to one or both parties involved. It is typically observed between individuals of closely related species, often upon secondary contact. In both vertebrates and invertebrates, Reproductive Interference is frequently referred to as 'Satyrisation'. It can manifest in various ways, ranging from blocking or reducing the efficacy of mating signals, through to negative effects of heterospecific copulations and the production of sterile or infertile hybrid offspring. The negative fitness effects of Satyrisation in reciprocal matings between species are often asymmetric and it is this aspect, which is most relevant to, and can offer utility in, pest management. In this review, we focus on Satyrisation and outline the mechanisms through which it can operate. We illustrate this by using test cases, and we consider the underlying reasons why the reproductive interactions that comprise Satyrisation occur. We synthesise the key factors affecting the expression of Satyrisation and explore how they have potential utility in developing new routes for the management and control of harmful insects. We consider how Satyrisation might interact with other control mechanisms, and conclude by outlining a framework for its use in control, highlighting some of the important next steps.

Imported Dengue Case Numbers and Local Climatic Patterns Are Associated with Dengue Virus Transmission in Florida, USA

Aedes aegypti mosquitoes are the main vector of dengue viruses globally and are present throughout much of the state of Florida (FL) in the United States of America. However, local transmission of dengue viruses in FL has mainly occurred in the southernmost counties; specifically Monroe and Miami-Dade counties. To get a better understanding of the ecologic risk factors for dengue fever incidence throughout FL, we collected and analyzed numerous environmental factors that have previously been connected to local dengue cases in disease-endemic regions. We analyzed these factors for each county-year in FL, between 2009–2019, using negative binomial regression. Monthly minimum temperature of 17.5–20.8 °C, an average temperature of 26.1–26.7 °C, a maximum temperature of 33.6–34.7 °C, rainfall between 11.4–12.7 cm, and increasing numbers of imported dengue cases were associated with the highest risk of dengue incidence per county-year. To our knowledge, we have developed the first predictive model for dengue fever incidence in FL counties and our findings provide critical information about weather conditions that could increase the risk for dengue outbreaks as well as the important contribution of imported dengue cases to local establishment of the virus in Ae. aegypti populations.

Metabolic Resistance in Permethrin-Resistant Florida Aedes aegypti (Diptera: Culicidae)

Simple Summary

Pyrethroid-oriented vector control programs have increased worldwide to control adult Aedes aegypti mosquitoes and quell Aedes-borne disease epidemics. Due to years of pyrethroid use, resistance to pyrethroids in Ae. aegypti has become a global issue. In Florida, permethrin is the most common pyrethroid adulticide active ingredient used to control mosquito populations. Thus far, all wild Florida Ae. aegypti populations tested against permethrin have been found to be resistant. Metabolic resistance is a major mechanism of resistance in insects in which enzyme-mediated reactions cause the degradation or sequestration of insecticides. We performed assays to investigate the presence of metabolic resistance in 20 Florida Ae. aegypti populations and found that 11 populations (55%) exhibited metabolic resistance due to the action of at least one of three classes of metabolizing enzymes: oxidases, esterases, and glutathione transferases. Additionally, we identified two metabolic enzyme inhibitors: S.S.S-tributyl phosphorotrithioate (DEF; inhibits esterase activity) and diethyl maleate (DM; inhibits glutathione transferase activity), in addition to the commonly used piperonyl butoxide (PBO; inhibits oxidase activity), which were able to increase the efficacy of permethrin against resistant Ae. aegypti populations. Pre-exposure to DEF, PBO, and DM resulted in increased mortality after permethrin exposure in eight (73%), seven (64%), and six (55%) of the Ae. aegypti populations, respectively. Increasing the effectiveness of pyrethroids is important for mosquito control, as it is the primary method used for adult control during mosquito-borne disease outbreaks. Considering that DEF and DM performed similarly to PBO, they may be good candidates for inclusion in formulated pyrethroid products to increase their efficacy against resistant mosquitoes.

Abstract

Aedes aegypti is the principal mosquito vector for many arthropod-borne viruses (arboviruses) including dengue, chikungunya, and Zika. In the United States, excessive permethrin use has led to a high frequency of resistance in mosquitoes. Insecticide resistance is a significant obstacle in the struggle against vector-borne diseases. To help overcome metabolic resistance, synergists that inhibit specific metabolic enzymes can be added to formulated pyrethroid products. Using modified CDC bottle bioassays, we assessed the effect of three inhibitors (piperonyl butoxide (PBO), which inhibits oxidase activity; S.S.S-tributyl phosphorotrithioate (DEF), which inhibits esterase activity; and diethyl maleate (DM), which inhibits glutathione transferase activity) + permethrin. We performed these against 20 Florida Ae. aegypti populations, all of which were resistant to permethrin. Our data indicated that 11 out of 20 populations (55%) exhibited metabolic resistance. Results revealed 73% of these populations had significant increases in mortality attributed to DEF + permethrin, 64% to PBO + permethrin, and 55% to DM + permethrin compared to permethrin alone. Currently, PBO is the only metabolic enzyme inhibitor added to formulated pyrethroid products used for adult mosquito control. Our results suggest that the DEF and DM inhibitors could also be useful additives in permethrin products, especially against metabolically resistant Ae. aegypti mosquitoes. Moreover, metabolic assays should be conducted to better inform mosquito control programs for designing and implementing integrated vector management strategies.

Mosquito Control Priorities in Florida-Survey Results from Florida Mosquito Control Districts

Florida lies within a subtropical region where the climate allows diverse mosquito species including invasive species to thrive year-round. As of 2021, there are currently 66 state-approved Florida Mosquito Control Districts, which are major stakeholders for Florida public universities engaged in mosquito research. Florida is one of the few states with extensive organized mosquito control programs. The Florida State Government and Florida Mosquito Control Districts have long histories of collaboration with research institutions. During fall 2020, we carried out a survey to collect baseline data on the current control priorities from Florida Mosquito Control Districts relating to (1) priority control species, (2) common adult and larval control methods, and (3) major research questions to address that will improve their control and surveillance programs. The survey data showed that a total of 17 distinct mosquito species were considered to be priority control targets, with many of these species being understudied. The most common control approaches included truck-mounted ultra-low-volume adulticiding and biopesticide-based larviciding. The districts held interest in diverse research questions, with many prioritizing studies on basic science questions to help develop evidence-based control strategies. Our data highlight the fact that mosquito control approaches and priorities differ greatly between districts and provide an important point of comparison for other regions investing in mosquito control, particularly those with similar ecological settings, and great diversity of potential mosquito vectors, such as in Florida. Our findings highlight a need for greater alignment of research priorities between mosquito control and mosquito research. In particular, we note a need to prioritize filling knowledge gaps relating to understudied mosquito species that have been implicated in arbovirus transmission.

Displacement of Aedes albopictus by Aedes aegypti in Gainesville, Florida

Aedes aegypti and Ae. albopictus are invasive mosquitoes, capable of vectoring arboviruses such as dengue, chikungunya, yellow fever, and Zika. Recent shifts in spatial distribution indicate there is a resurgence of Ae. aegypti in certain regions of Florida. After a 26-year absence, Ae. aegypti larvae were collected in a downtown neighborhood in Gainesville, Florida, in November 2019. Subsequent surveys confirmed that Ae. albopictus was completely displaced by Ae. aegypti in this neighborhood, whereas Ae. albopictus and Ae. aegypti coexisted around this community focus, and Ae. albopictus alone has been found elsewhere in the city and county since the 1990s. Field surveys revealed that Ae. aegypti is resurging in the downtown area of Gainesville and is actively dispersing to adjacent neighborhoods. Thus, Ae. aegypti could potentially replace Ae. albopictus across more of urban Gainesville in north-central Florida, as reported recently in coastal cities of northeastern Florida.

Collection and Rearing of Container Mosquitoes and a 24-h Addition to the CDC Bottle Bioassay

Container mosquitoes (Diptera: Culicidae) oviposit their eggs in both natural and artificial containers. Many container mosquito species also serve as important vectors of disease-causing pathogens including Aedes aegypti, Ae. albopictus, and Ae. triseriatus. Control of these species can be done through the use of adulticide sprays. The efficacy of these treatments is highly dependent on the insecticide susceptibility status of the local mosquito populations. This paper provides protocols on collecting and rearing container mosquitoes for use in the Centers for Disease Control and Prevention (CDC) bottle bioassay. A brief description of the CDC bottle bioassay is provided as well as a standardized protocol for the incorporation of a 24-h mortality to the CDC bottle bioassay. Results from this 24-h holding addition to the CDC bottle bioassay reveal that some forms of resistance may be missed without the incorporation of the additional mortality reading. These protocols provide a foundation for new laboratories to establish rearing protocols and begin conducting resistance monitoring.

Baseline Susceptibility Status of Florida Populations of Aedes aegypti (Diptera: Culicidae) and Aedes albopictus

Resistance to insecticides used to control mosquito vectors threatens the ability of mosquito-control organizations to protect public health. Aedes aegypti (Linnaeus) and Aedes albopictus (Skuse) are invasive species widely distributed throughout Florida and have been implicated in recent epidemics of Zika, dengue, and chikungunya viruses. Knowledge of the susceptibility status of these mosquito species to pyrethroid and organophosphate active ingredients (AIs) is needed to inform product selection and treatment decisions. The susceptibility of 37 Ae. aegypti and 42 Ae. albopictus populations from Florida was assessed in response to six pyrethroid and three organophosphate AIs using the CDC bottle bioassay method. Of all bioassays completed with a pyrethroid AI, 95% for Ae. aegypti and 30% for Ae. albopictus resulted in a resistant outcome. For organophosphate AIs, ~31% of assays conducted for both species were classified as resistant. The highest frequency of susceptibility for both species was observed in response to the organophosphate AI, naled. Lambda-cyhalothrin was the only pyrethroid to result in a susceptible status for Ae. aegypti and also had the highest frequency of susceptibility for Ae. albopictus. Resistance was detected to every AI tested for both Ae. aegypti and Ae. albopictus, but there was a pronounced trend of pyrethroid resistance in Florida populations of Ae. aegypti. The results of this work provide evidence for the need to decrease reliance on pyrethroids and to implement different methods of control of Ae. aegypti in Florida.