Point Protection with Transfluthrin against Musca domestica L. in a Semi-Field Enclosure

House flies are notoriously difficult to control, owing to their tendency to live in close relationships with humans and their livestock, and their rapid development of resistance to chemical controls. With this in mind, we explored an alternative chemical control, a spatial repellent to deter Musca domestica L. from points we wanted to protect (i.e., a baited trap). Our results demonstrated that the synthetic spatial repellent, transfluthrin, is effective in preventing M. domestica adults from entering protected traps for both a susceptible strain (CAR21) and a field-acquired permethrin-resistant strain (WHF; 24 h LD50 resistance ratio of 150), comprising 22% and 28% of the total number of flies collected, respectively. These results are promising and demonstrate that transfluthrin can be an effective spatial repellent to protect points of interest where needed.

Aedes aegypti Controls AE. Aegypti: SIT and IIT-An Overview

The sterile insect technique (SIT) and the incompatible insect technique (IIT) are emerging and potentially revolutionary tools for controlling Aedes aegypti (L.), a prominent worldwide mosquito vector threat to humans that is notoriously difficult to reduce or eliminate in intervention areas using traditional integrated vector management (IVM) approaches. Here we provide an overview of the discovery, development, and application of SIT and IIT to Ae. aegypti control, and innovations and advances in technology, including transgenics, that could elevate these techniques to a worldwide sustainable solution to Ae. aegypti when combined with other IVM practices.

Does prior exposure to larvicides influence dengue virus susceptibility in Aedes aegypti (Diptera: Culicidae)?

Control of mosquito vector populations is primarily intended to reduce the transmission of pathogens they transmit. Use of chemical controls, such as larvicides, can have unforeseen consequences on adult traits if not applied properly. The consequences of under application of larvicides are little studied, specifically the impacts on pathogen infection and transmission by the vectors that survive exposure to larvicides. We compared vector susceptibility of Aedes aegypti (L.) for dengue virus, serotype 1 (DENV-1) previously exposed as larvae to an LC50 of different classes of insecticides as formulated larvicides. Larval exposure to insect growth regulators (methoprene and pyriproxyfen) significantly increased susceptibility to infection of DENV-1 in Ae. aegypti adults but did not alter disseminated infection or transmission. Larval exposure to temephos, spinosad, and Bti did not increase infection, disseminated infection, or transmission of DENV-1. Our findings describe a previously under observed phenomenon, the latent effects of select larvicides on mosquito vector susceptibility for arboviruses. These data suggest that there are unintended consequences of sublethal exposure to select larvicides that can influence susceptibility of Ae. aegypti to DENV infection, and indicates the need for further investigation of sublethal effects of insecticides on other aspects of mosquito biology, especially those parameters relevant to a mosquitoes ability to transmit arboviruses (life span, biting behavior, extrinsic incubation period).

Transfluthrin diffusers do not protect two-person US military tents from mosquitoes in open field and canopy warm-temperate habitats

Spatial repellents are volatile or volatilized chemicals that may repel arthropod vectors in free space, preventing bites and reducing the potential for pathogen transmission. In a 21-week field study, we investigated the efficacy of passive transfluthrin-impregnated diffusers placed in two-person United States (US) military tents located in canopy and open field habitats in north Florida to prevent mosquitoes from entering. Mosquito collections with US Centers for Disease Control and Prevention traps baited with light and carbon dioxide were conducted weekly for weeks 0-4, every two weeks for weeks 5-10, and monthly for weeks 11-21. Our results demonstrated that these transfluthrin-impregnated devices did not function as spatial repellents as expected and did not create a mosquito-free zone of protection. Instead, we observed consistently higher collections of mosquitoes from tents with transfluthrin-impregnated diffusers, and higher rates of mosquito mortality in collections from tents with transfluthrin diffusers, compared to untreated control tents. Based on these findings we do not recommend the use of passive transfluthrin-impregnated diffusers for mosquito protection in two-person US military tents in warm-temperate environments similar to north Florida.

Structural Exploration of Novel Pyrethroid Esters and Amides for Repellent and Insecticidal Activity against Mosquitoes

The emergence of pyrethroid-resistant mosquitoes is a worldwide problem that necessitates further research into the development of new repellents and insecticides. This study explored the modification of existing pyrethroid acids to identify structural motifs that might not be affected by kdr active site mutations that elicit pyrethroid resistance. Because synthetic pyrethroids almost always contain activity-dependent chiral centers, we chose to focus our efforts on exploring alkoxy moieties of esters obtained with 1R-trans-permethrinic and related acids, which we showed in previous studies to have repellent and/or repellent synergistic properties. To this end, compounds were synthesized and screened for spatially acting repellency and insecticidal activity against the susceptible, Orlando, and pyrethroid-resistant, Puerto Rico, strains of Aedes aegypti mosquito. Screening utilized a high-throughput benchtop glass tube assay, and the compounds screened included a mixture of branched, unbranched, aliphatic, halogenated, cyclic, non-cyclic, and heteroatom-containing esters. Structure-activity relationships indicate that n-propyl, n-butyl, n-pentyl, cyclobutyl, and cyclopentyl substituents exhibited the most promising repellent activity with minimal kdr cross resistance. Preliminary testing showed that these small alcohol esters can be synergistic with phenyl amides and pyrethroid acids. Further derivatization of pyrethroid acids offer an interesting route to future active compounds, and while mosquitoes were the focus of this work, pyrethroid acids and esters have potential for use in reducing pest populations and damage in cropping systems as well.

The increasing threat of Rift Valley fever virus globalization: strategic guidance for protection and preparation

Rift Valley fever virus (RVFV) (Bunyavirales: Phlebovirus) is a prominent vector-borne zoonotic disease threat to global agriculture and public health. Risks of introduction into nonendemic regions are tied to changing climate regimes and other dynamic environmental factors that are becoming more prevalent, as well as virus evolutionary factors and human/animal movement. Endemic to the African continent, RVFV has caused large epizootics at the decadal scale since the early 20th century but has spread to the Arabian Peninsula and shows increasing patterns of interepizootic transmission on the annual scale. This virus can be transmitted by mosquitoes as well as through direct contact with infected tissues and can cause sporadic to widespread morbidity and mortality in domestic ungulate livestock as well as humans. High viremias in infected livestock moved for legal and illegal trade as well as in infected mosquitoes or human travelers can spread this virus worldwide. With increasing global commerce, it is likely RVFV will be introduced to new areas with suitable hosts, mosquito vector species, and environments. However, the strong mosquito component of RVFV epidemiology combined with advancements in vaccines, diagnostics, and virus evolutionary factors create opportunities for strategies to leverage models of connectivity among potential source and emerging regions to target surveillance and mitigation activities to reduce the risk of RVFV introduction, or contain the virus should it be introduced, into new regions.

Developing the radiation-based sterile insect technique (SIT) for controlling Aedes aegypti: identification of a sterilizing dose

BACKGROUND

The sterile insect technique (SIT) is emerging as a tool to supplement traditional pesticide-based control of Aedes aegypti, a prominent mosquito vector of microbes that has increased the global burden of human morbidity and mortality over the past 50 years. SIT relies on rearing, sterilizing and releasing large numbers of male mosquitoes that will mate with fertile wild females, thus reducing production of offspring from the target population. In this study, we investigated the effects of ionizing radiation (gamma) on male and female survival, longevity, mating behavior, and sterility of Ae. aegypti in a dose-response design. This work is a first step towards developing an operational SIT field suppression program against Ae. aegypti in St. Augustine, Florida, USA.

RESULTS

Exposing late-stage pupae to 50 Gy of radiation yielded 99% male sterility while maintaining similar survival of pupae to adult emergence, adult longevity and male mating competitiveness compared to unirradiated males. Females were completely sterilized at 30 Gy, and when females were dosed with 50 Gy, they had a lower incidence of blood-feeding than unirradiated females.

CONCLUSION

Our work suggests that an ionizing radiation dose of 50 Gy should be used for future development of operational SIT in our program area because at this dose males are 99% sterile while maintaining mating competitiveness against unirradiated males. Furthermore, females that might be accidentally released with sterile males as a result of errors in sex sorting also are sterile and less likely to blood-feed than unirradiated females at our 50 Gy dose. © 2022 Society of Chemical Industry.

Co-occurrence probabilities between mosquito vectors of West Nile and Eastern equine encephalitis viruses using Markov Random Fields (MRFcov)

Mosquito vectors of eastern equine encephalitis virus (EEEV) and West Nile virus (WNV) in the USA reside within broad multi-species assemblages that vary in spatial and temporal composition, relative abundances and vector competence. These variations impact the risk of pathogen transmission and the operational management of these species by local public health vector control districts. However, most models of mosquito vector dynamics focus on single species and do not account for co-occurrence probabilities between mosquito species pairs across environmental gradients. In this investigation, we use for the first time conditional Markov Random Fields (CRF) to evaluate spatial co-occurrence patterns between host-seeking mosquito vectors of EEEV and WNV around sampling sites in Manatee County, Florida. Specifically, we aimed to: (i) quantify correlations between mosquito vector species and other mosquito species; (ii) quantify correlations between mosquito vectors and landscape and climate variables; and (iii) investigate whether the strength of correlations between species pairs are conditional on landscape or climate variables. We hypothesized that either mosquito species pairs co-occur in patterns driven by the landscape and/or climate variables, or these vector species pairs are unconditionally dependent on each other regardless of the environmental variables. Our results indicated that landscape and bioclimatic covariates did not substantially improve the overall model performance and that the log abundances of the majority of WNV and EEEV vector species were positively dependent on other vector and non-vector mosquito species, unconditionally. Only five individual mosquito vectors were weakly dependent on environmental variables with one exception, Culiseta melanura, the primary vector for EEEV, which showed a strong correlation with woody wetland, precipitation seasonality and average temperature of driest quarter. Our analyses showed that majority of the studied mosquito species' abundance and distribution are insignificantly better predicted by the biotic correlations than by environmental variables. Additionally, these mosquito vector species may be habitat generalists, as indicated by the unconditional correlation matrices between species pairs, which could have confounded our analysis, but also indicated that the approach could be operationalized to leverage species co-occurrences as indicators of vector abundances in unsampled areas, or under scenarios where environmental variables are not informative.

Lethal and Sublethal Concentrations of Formulated Larvicides Against Susceptible Aedes aegypti

Chemical control of vectors depends on the effective application of formulated insecticides. In this study we evaluated formulated larvicides using a larval bioassay against susceptible Aedes aegypti. The estimated larvicide lethal concentrations for 50% mortality (LC50s) were 25.7 μg/liter (Natular 2EC), 3.13 μg/liter (Abate 4E), 0.43 μg/liter (Altosid), 0.03 μg/liter (Nyguard), and 500.6 ITU/liter (VectoBac12AS containing Bacillus thuringiensis israelensis). Sublethal effects were identified and documented from adults that survived exposure to these estimated LC50s (body size and sex proportion). We observed changes in net growth as measured by adult wing lengths. For those larvae exposed to estimated LC50s, the average size of adults was between 0.1% and 10.6% smaller for males and between 1.1% and 13.6% smaller for females compared to controls. Sex proportions varied between larvicides, but some were significantly different from the control, favoring greater survival of females than males.

Does severe hypoxia during irradiation of Aedes aegypti pupae improve sterile male performance?

Background

The yellow fever mosquito, Aedes aegypti, vectors several pathogens responsible for human diseases. As a result, this mosquito species is a priority for control by mosquito control districts in Florida. With insecticide resistance development becoming a concern, alternative control strategies are needed for Ae. aegypti. Sterile insect technique (SIT) is an increasingly popular option that is being explored as a practical area-wide control method. However, questions about sterile male performance persist. The objectives of this study were to determine the extent to which hypoxia exposure prior to and during irradiation effects the longevity, activity and mating competitiveness of sterile male Ae. aegypti.

Methods

Male longevity was monitored and analyzed using Cox regression. Mosquito activity was recorded by an infrared beam sensor rig that detected movement. Competing models were created to analyze movement data. Fecundity and fertility were measured in females mated with individual males by treatment and analyzed using one-way ANOVAs. Mating competition studies were performed to compare both hypoxia and normoxia treated sterile males to fertile males. Competitiveness of groups was compared using Fried’s competitiveness index.

Results

First, we found that subjecting Ae. aegypti pupae to 1 h of severe hypoxia (< 1 kPa O2) did not directly increase mortality. One hour of hypoxia was found to prevent decreases in longevity of irradiated males compared to males irradiated in normoxic conditions. Exposure to hypoxia prior to irradiation did not significantly improve activity of sterile males except at the highest doses of radiation. Hypoxia did significantly increase the required dose of radiation to achieve > 95% male sterility compared to males irradiated under normoxic conditions. Males sterilized after an hour in hypoxic conditions were significantly more competitive against fertile males compared to males irradiated under normoxic conditions despite requiring a higher dose of radiation to achieve sterility.

Conclusions

Hypoxia was found to greatly improve key performance metrics in sterile male Ae. aegypti without any significant drawbacks. Little work other than increasing the target dose for sterility needs to be conducted to incorporate hypoxia into SIT programs. These results suggest that SIT programs should consider including hypoxia in their sterile male production workflow.

Graphical Abstract

Assessing transfluthrin mortality against Aedes aegypti and Culex quinquefasciatus inside and outside US military tents in a northern Florida environment

Mortality caused by passive resin transfluthrin diffusers (∼5 mg AI per 24 h release rate) suspended in small 2-person tents was measured for colony-reared sentinel pyrethroid susceptible Aedes aegypti and Culex quinquefasciatus female mosquitoes, as well as a pyrethroid-resistant strain of Aedes aegypti, in a USA military field camp scenario. Mortality effects were investigated for impact by factors such as sentinel cage location (inside tent, tent doorway and outside tent), exposure time (15, 30, 45 and 60 min), and environmental temperature (°C), all of which were examined over an 8-week period. Analyses determined there was a significant interaction between mosquito strain and transfluthrin susceptibility, with the two susceptible strains experiencing significantly greater mean mortality than the resistant Ae. aegypti strain. Significant differences were likewise observed between the mosquito strains over the 8-week study period, where study week and temperature were both positively correlated with an increase in observed mean mosquito mortality. Mosquito proximity to the transfluthrin diffusers was also influenced by week and showed that sentinel cage placement in the environment demonstrates different mortality measurements, depending on the environmental conditions. The length of exposure to transfluthrin, however, was determined to not significantly impact transfluthrin efficacy on the examined mosquito strains, although increased exposure did result in increased susceptible strain mortality. These results suggest that transfluthrin is highly effective in causing mortality against susceptible Ae. aegypti and Cx. quinquefasciatus mosquitoes under field conditions but is minimally effective against pyrethroid-resistant Ae. aegypti mosquitoes. Transfluthrin-infused devices are influenced by environmental factors that can combine to impact mosquito mortality in the field.

Resistance-Breaking Insecticidal Activity of New Spatial Insecticides against Aedes aegypti

The use of N-aryl amide derivatives as spatially acting insecticides remains relatively unexplored. To expand this knowledge, we synthesized eighty-nine N-aryl amide analogues and screened them for mortality against an insecticide-susceptible strain of Aedes aegypti mosquitoes, Orlando (OR), using a vapor exposure glass tube assay. Of the screened compounds, twenty-two produced >92% mortality at 24 h and warranted further investigation to determine LC₅₀ values. Fifteen of these analogues had LC₅₀ values within 2 orders of magnitude of transfluthrin, and of significant interest, N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-2,2,3,3,3-pentafluoropropanamide (compound 70) was nearly as potent as transfluthrin and exhibited greater toxicity than metofluthrin when screened against OR A. aegypti. Compounds exhibiting potent toxicity against OR A. aegypti or whose structure-activity relationship potentially offered beneficial insights into structure optimization were screened against the insecticide-resistant, Puerto Rico (PR), strain of A. Aegypti, and it was discovered that not only did these N-arylamides typically show little resistance, some such as N-(2,6-dichloropyridin-4-yl)-2,2,3,3,4,4,4-heptafluorobutanamide (compound 36) and 2,2,3,3,4,4,4-heptafluoro-N-(3,4,5-trifluorophenyl)butanamide (compound 40) were actually more potent against the PR mosquitoes. Due to this promising insecticidal activity, five compounds were administered orally to mice to determine acute oral rodent toxicity. All five compounds were found to have mouse oral toxicity LD₅₀ values well above the minimum safe level as set by the Innovative Vector Control Consortium (50 mg/kg). In addition to the promising biological activity documented here, we report the structure-activity relationship analysis used to guide the derivatization approach taken and to further inform future efforts in the development of N-arylamides as potential resistance-breaking, spatially acting insecticides.

Preparing Irradiated and Marked Male Aedes aegypti Mosquitoes for Release in an Operational Sterile Insect Technique Program

The control of such human diseases as dengue, Zika, and chikungunya relies on the control of their vector, the Aedes aegypti mosquito, because there is no prevention. Control of mosquito vectors can rely on chemicals applied to the immature and adult stages, which can contribute to the mortality of non-targets and more importantly, lead to insecticide resistance in the vector. The sterile insect technique (SIT) is a method of controlling populations of pests through the release of sterilized adult males that mate with wild females to produce non-viable offspring. This paper describes the process of producing sterile males for use in an operational SIT program for the control of Aedes aegypti mosquitoes. Outlined here are the steps used in the program including rearing and maintaining a colony, separating male and female pupae, irradiating and marking adult males, and shipping Aedes aegypti males to the release site. Also discussed are procedural caveats, program limitations, and future objectives.

Spatial Repellents Protect Small Perimeters from Riceland Mosquitoes in a Warm-Humid Environment

Recent experiments suggest spatial repellents may significantly reduce biting pressure from host-seeking riceland mosquitoes, such as Anopheles quadrimaculatus, in a warm-humid open-field habitat. However, little is known regarding efficacy of these formulations in partially enclosed spaces where US military personnel may be sheltered or concealed in an operational environment. In this study we investigated the capability of 3 spatial repellents-metofluthrin, linalool, and d-cis/trans allethrin-to reduce mosquito incursion into small open-top enclosures of US military camouflage netting. We found that metofluthrin was more effective in partially enclosed spaces compared with the open field, whereas both linalool and d-cis/trans allethrin provided superior protection in the open. These findings support strategic selection of spatial repellents depending on the environment immediately surrounding the host.

A Survey of Chemoreceptive Responses on Different Mosquito Appendages

Research on the functions of insect chemoreceptors have primarily focused on antennae (olfactory receptors) and mouthparts (gustatory receptors). However, chemoreceptive sensilla are also present on other appendages, such as the leg tarsi and the anterior wing margin, and their specific roles in chemoreception and mosquito behavior remain largely unknown. In this study, electrophysiological analyses in an electroantennogram recording format were performed on Aedes aegypti (L., Diptera: Culicidae) antennae, mouthparts, tarsi, and wings during exposure to a variety of insect repellent and attractant compounds. The results provide evidence that the tarsi and wings can sense chemicals in a gaseous form, and that the odors produce differing responses on different appendages. The most consistent and strongest response occurred when exposed to triethylamine (TEA). Antennae and mouthparts showed nearly identical responses pattern to all tested compounds, and their rank orders of effectiveness were similar to those of fore- and mid-leg tarsi. Hindleg tarsi only responded to TEA, indicating that the hind legs are not as chemoreceptive. Wings responded to a range of odorants, but with a different rank order and voltage amplitude. Insights gleaned into the function of these appendages in insect chemoreception are discussed.

Vapor phase repellency and insecticidal activity of pyridinyl amides against anopheline mosquitoes

It is important to identify repellents that can provide reliable protection from arthropod biting and prevent arthropod-borne diseases, such as malaria. In the present study, the spatial repellent activity and toxicity of two novel pyridinyl amides (1 and 2) were evaluated against Anopheles albimanus, Anopheles quadrimaculatus, and Anopheles gambiae. In vapor repellency bioassays, compound 2 was generally more effective than DEET and 2-undecanone, while compound 1 was about as active as these standards. Overall, transfluthrin was the most active compound for inducing anopheline mosquito repellency, knockdown, and lethality. Although they were not the most active repellents, the two experimental amides produced the largest electroantennographic responses in female antennae. They also displayed modest toxicity to anopheline mosquitoes. Significant synergism of repellency was observed for the mixture of a pyrethroid-derived acid and the repellent 2-undecanone against anopheline mosquitoes, similar to that observed previously in Aedes aegypti. Overall, this study provides insight for further synthesis of alternative amide compounds for use as spatial treatments.

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Two experimental pyridyl amides were synthesized.

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They were more repellent than DEET, equal to 2-undecanone and less than transfluthrin.

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They were about as toxic as DEET and 2-undecanone, but less than transfluthrin.

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Experimental amides performed about the same across all anopheline species.

Reanalysis of the 2000 Rift Valley fever outbreak in Southwestern Arabia

The first documented Rift Valley hemorrhagic fever outbreak in the Arabian Peninsula occurred in northwestern Yemen and southwestern Saudi Arabia from August 2000 to September 2001. This Rift Valley fever outbreak is unique because the virus was introduced into Arabia during or after the 1997–1998 East African outbreak and before August 2000, either by wind-blown infected mosquitos or by infected animals, both from East Africa. A wet period from August 2000 into 2001 resulted in a large number of amplification vector mosquitoes, these mosquitos fed on infected animals, and the outbreak occurred. More than 1,500 people were diagnosed with the disease, at least 215 died, and widespread losses of domestic animals were reported. Using a combination of satellite data products, including 2 x 2 m digital elevation images derived from commercial satellite data, we show rainfall and potential areas of inundation or water impoundment were favorable for the 2000 outbreak. However, favorable conditions for subsequent outbreaks were present in 2007 and 2013, and very favorable conditions were also present in 2016–2018. The lack of subsequent Rift Valley fever outbreaks in this area suggests that Rift Valley fever has not been established in mosquito species in Southwest Arabia, or that strict animal import inspection and quarantine procedures, medical and veterinary surveillance, and mosquito control efforts put in place in Saudi Arabia following the 2000 outbreak have been successful. Any area with Rift Valley fever amplification vector mosquitos present is a potential outbreak area unless strict animal import inspection and quarantine proceedures are in place.

Structure-Activity Relationship Analysis of Potential New Vapor-Active Insect Repellents

A total of 115 aryl amides were synthesized and screened for vapor repellency against the Orlando (OR) strain of Aedes aegypti mosquitoes. Of these compounds, 29 had 1 h repellency EC₅₀ values comparable to or better than N,N-diethyl-meta-toluamide (DEET, 1 h EC₅₀ value of 35 μg/cm²), with 2,2,3,3,3-pentafluoro-N-(4-fluorophenyl)propenamide (53) and 2,2,3,3,4,4,4-heptafluoro-N-(3,4,5-trifluorophenyl)butanamide (101) exhibiting the most potent EC₅₀ values of 4.5 and 2.9 μg/cm², respectively. The cross-resistance of select, highly potent, derivatives against the pyrethroid-resistant Puerto Rico (PR) strain of A. aegypti was also investigated, and little to no resistance was observed. When synergized with 1R-trans-permethrinic acid (TFA), compound 101 had a 1 h EC₅₀ value 6 times lower than metofluthrin against OR and 40 times lower against PR mosquitoes. Additionally, preliminary mammalian oral toxicity was screened for compounds 69 and 101, and both exhibited LD₅₀ values of >2000 mg/kg. The structure-activity relationship analysis, which guided the synthesis of these derivatives, is given, and key trends are highlighted to inform future analogue design.

Gamma-Irradiation Reduces Survivorship, Feeding Behavior, and Oviposition of Female Aedes aegypti

Aedes aegypti is a prominent disease vector that is difficult to control through traditional integrated vector management due to its cryptic peridomestic immature-stage habitat and adult resting behavior, increasing resistance to pesticide formulations approved by the US Environmental Protection Agency, escalating deregistration of approved pesticides, and slow development of new effective chemical control measures. One novel method to control Ae. aegypti is the sterile insect technique (SIT) that leverages the mass release of irradiated (sterilized) males to overwhelm mate choice of natural populations of females. However, one potential liability of SIT is sex sorting errors prior to irradiation, resulting in accidental release of females. Our goal in this study was to test the extent to which irradiation affects female life-history parameters to assess the potential impacts of releasing irradiated females accidentally sorted with males. In this study, we determined that a radiation dose ≥30 Gy-a dose sufficient to sterilize males while preserving their mating competitiveness-may substantially impact longevity, bloodfeeding, oviposition, and egg hatch rate of female Ae. aegypti after being irradiated as pupae. These findings could reduce public concern for accidental release of females alongside irradiated males in an operational Ae. aegypti SIT control program.

Transfluthrin Spatial Repellent on US Military Camouflage Netting Reduces Tabanids in a Warm-Temperate Environment

We investigated the capability of transfluthrin on US military camouflage netting to reduce collections of tabanid biting flies in a warm-temperate field environment on the Gulf Coast of Florida. We found that transfluthrin significantly reduced collections of a variety of medically and veterinarily important tabanids inside protected areas by up to 96% upon initial treatment and up to 74% after 20 days posttreatment. These results suggest that transfluthrin could be an effective element in the US Department of Defense integrated pest management system and leveraged in civilian scenarios to protect livestock and humans from potential mechanical transmission of pathogens and disruption of activities caused by painful bites.

Interactions of DEET and Novel Repellents With Mosquito Odorant Receptors

The carboxamide N,N-di-ethyl-meta-toluamide (DEET) is the most effective and widely used insect repellent today. However, drawbacks concerning the efficacy and the safety of the repellent have led to efforts to design new classes of insect repellents. Through quantitative structure-activity relationships, chemists have discovered two chemical groups of novel repellents: the acylpiperidines and the carboxamides, with the acylpiperidines generally more potent in biological assays. Although the exact mechanism of action of DEET and other repellents has not yet been thoroughly elucidated, previous research shows that the activity of insect odorant receptors are inhibited in the presence of repellents. The present electrophysiological study employs two-electrode voltage clamp with Xenopus laevis oocytes expressing AgOR2/AgOrco and AgOR8/AgOrco receptors to assess the effects of the novel repellents on Anopheles gambiae Giles (Insecta: Diptera: Culicidae) mosquito odorant receptors. The novel acylpiperidines and carboxamides reversibly inhibited (12-91%) odorant-evoked currents from both AgOR2/AgOrco and AgOR8/AgOrco receptors in a dose-dependent manner at all tested concentrations (30 μM to 1 mM). Furthermore, all the novel agents were more potent inhibitors of the receptors than DEET, with the acylpiperidines producing on average greater inhibition than the carboxamides. Interestingly, there was a correlation (r2 = 0.72) between the percentage inhibition of AgOR2/AgOrco receptor currents and protection times of the acylpiperidines. Our results add to existing evidence that the repellency of a compound is linked to its ability to disrupt the insect olfactory system and that the acylpiperidines could represent a class of more effective alternatives to the current gold standard, DEET.

Failure of Permethrin-Treated Military Uniforms to Protect Against a Laboratory-Maintained Knockdown-Resistant Strain of Aedes aegypti

Military forces and the recreational industry rely on the repellent properties of permethrin-treated fabrics and N,N-diethyl-meta-toluamide (deet)-based lotions to provide protection from disease vectors and hematophagous organisms. Concerns regarding efficacy have been raised as pyrethroid resistance becomes more common and recent publications present contradictory conclusions. In this preliminary study, consenting volunteers were exposed to pyrethroid-susceptible and pyrethroid-resistant Aedes aegypti strains while wearing sleeves of untreated or permethrin-treated army uniform fabric as well as with untreated or deet-treated exposed forearms. Deet was nearly 100% effective against both susceptible and resistant strains. However, permethrin treatment provided no significant protection against the resistant Puerto Rico strain relative to untreated control sleeves. These results confirm that pyrethroid-resistant vectors can negate the efficacy of permethrin-treated uniforms. Additional testing with resistant field strains is needed to better understand the risk to service members.

Pyrethroid-Derived Acids and Alcohols: Bioactivity and Synergistic Effects on Mosquito Repellency and Toxicity

Pyrethroids are one of the most commonly used classes of insecticides, and their acid and alcohol components are esterase degradation products, usually considered to be biologically inactive. In this study, it was found that several pyrethroid acids had a spatial repellent activity that was greater than DEET, often more active than the parent pyrethroids, and showed little cross resistance in a pyrethroid-resistant Puerto Rico strain of Aedes aegypti mosquitoes. Further investigation revealed that the acids can synergize not only contact repellent standards but also other pyrethroid components as well as the parent pyrethroids themselves. Synergism by the pyrethroid acids is expressed as both increased spatial repellency and vapor toxicity as well as human bite protection. Electrophysiological studies confirmed that pyrethroid acids (100 μM) had no effect on neuronal discharge in larval Drosophila melanogaster CNS and were detected by electroantennography, and there was little resistance to olfactory sensing of these acids in antennae from Puerto Rico strain mosquitoes carrying kdr mutations. Thus, the data suggest that the pyrethroid acids have a different mode of action than the parent pyrethroids, unrelated to the voltage-sensitive sodium channel. The results highlight the potential of pyrethroid acids to be useful in future repellent formulations.

Pesticide Misting System Enhances Residual Pesticide Treatment of HESCO Geotextile

Residual pesticide treatment of US military materials such as camouflage netting and HESCO blast wall geotextile is an effective way to reduce biting pressure within protected perimeters. However, residual treatments eventually wane and require retreatment in situ, which may not be possible or practical in military scenarios. One solution is to install pesticide misting systems on treated perimeters, which may additively enhance residual treatments, and gradually retreat perimeter material as misted pesticide settles. In this investigation we show that pesticide misting can extend efficacy of residual treatments on HESCO geotextile against mosquitoes and sand flies in a hot-arid desert environment by 1-2 wk.

Effectiveness of Aquatain® AMF and Cocobear™ Larvicidal Oil Against Culex quinquefasciatus Larvae and Pupae in an Organically Enhanced Aquatic Habitat

The efficacy of CocoBear™ Larvicidal Oil and Aquatain^® AMF Liquid Mosquito Film against larval and pupal Culex quinquefasciatus was compared (at maximum label field application rates) when applied to concrete troughs treated with composted cow manure. At 1 h posttreatment, CocoBear provided significantly greater reduction of mosquito larvae than Aquatain, but both products were equally effective in producing >97% control at 24 h. Each product provided >98% pupal reduction at 1 h posttreatment, with complete elimination of pupae from troughs at 24 h. CocoBear and Aquatain proved to be equally effective against Cx. quinquefasciatus immatures in organically enriched aquatic habitats.

Transfluthrin Spatial Repellent on US Military Materials Reduces Culex tarsalis Incursion in a Desert Environment

Standard residual pesticides applied to US military materials such as camouflage netting can reduce mosquito biting pressure in the field but may contribute to the evolution of resistance. However, residual applications of a spatial repellent such as transfluthrin could allow mosquitoes the opportunity to escape, only inducing mortality if insects linger, for example after becoming trapped in a treated tent. In this study we investigated the capability of transfluthrin on 2 types of US military material to reduce natural populations of disease vector mosquitoes in a cool-arid desert field environment in southern California. We found that transfluthrin could reduce Culex tarsalis incursion into protected areas by up to 100% upon initial treatment and up to 45% for at least 16 days posttreatment, showing that this compound could be an effective element in the US Department of Defense integrated vector management system appropriate for further study.

Reduced effectiveness of repellents in a pyrethroid-resistant strain of Aedes aegypti (Diptera: culicidae) and its correlation with olfactory sensitivity

BACKGROUND

The mosquito, Aedes aegypti (Diptera: Culicidae), is a vector of dengue fever, zika, chikungunya, and yellow fever viruses, and in many areas possesses significant levels of resistance to pyrethroids. Behavioral performance was assessed in 15, 30, and 60 min exposures in a high throughput vapor phase spatial repellency assay to three contact repellent standards: N,N-diethyl-3-methylbenzamide (DEET), ethyl 3-[acetyl(butyl)amino] propanoate (IR3535), and 2-undecanone, as well as pyrethrum extract, transfluthrin, and metofluthrin in susceptible (Orlando) and a pyrethroid-resistant Puerto Rico strain of Aedes aegypti. Additionally, electroantennographic studies were used to investigate the antennal sensitivities to these compounds in both strains.

RESULTS

Resistance was found to all tested insect repellents in the Puerto Rico strain of Ae. aegypti. Resistance ratios at the different time points were about 2 for DEET, 3 for 2-undecanone, and 12 for IR3535. Resistance was also observed to pyrethrum extract (∼9-fold), transfluthrin (∼5-fold), and metofluthrin (∼48-fold) in repellent behavioral response. Electrophysiological analysis found decreased antennal sensitivity to all repellents tested, consistent with their behavioral effects.

CONCLUSION

The reduced sensitivity to these repellents may represent a fitness cost arising from the kdr mutation present in Puerto Rico Aedes aegypti. This work highlights the need for understanding collateral effects from the evolution of pesticide resistance in mosquitoes, and the importance of finding alternative strategies to control resistance development. © 2019 Society of Chemical Industry.

Predicting Abundances of Aedes mcintoshi, a primary Rift Valley fever virus mosquito vector

Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic arbovirus with important livestock and human health, and economic consequences across Africa and the Arabian Peninsula. Climate and vegetation monitoring guide RVFV forecasting models and early warning systems; however, these approaches make monthly predictions and a need exists to predict primary vector abundances at finer temporal scales. In Kenya, an important primary RVFV vector is the mosquito Aedes mcintoshi. We used a zero-inflated negative binomial regression and multimodel averaging approach with georeferenced Ae. mcintoshi mosquito counts and remotely sensed climate and topographic variables to predict where and when abundances would be high in Kenya and western Somalia. The data supported a positive effect on abundance of minimum wetness index values within 500 m of a sampling site, cumulative precipitation values 0 to 14 days prior to sampling, and elevated land surface temperature values ~3 weeks prior to sampling. The probability of structural zero counts of mosquitoes increased as percentage clay in the soil decreased. Weekly retrospective predictions for unsampled locations across the study area between 1 September and 25 January from 2002 to 2016 predicted high abundances prior to RVFV outbreaks in multiple foci during the 2006-2007 epizootic, except for two districts in Kenya. Additionally, model predictions supported the possibility of high Ae. mcintoshi abundances in Somalia, independent of Kenya. Model-predicted abundances were low during the 2015-2016 period when documented outbreaks did not occur, although several surveillance systems issued warnings. Model predictions prior to the 2018 RVFV outbreak indicated elevated abundances in Wajir County, Kenya, along the border with Somalia, but RVFV activity occurred west of the focus of predicted high Ae. mcintoshi abundances.

Insecticidal and repellent properties of novel trifluoromethylphenyl amides III

The adulticidal, larvicidal, and repellent activity of 18 trifluoromethylphenyl amides (TFMPAs) was determined against Aedes aegypti mosquitoes. The compounds studied are the third generation designed from active structures of the previous two generations. N-(3,5-Bis(trifluoromethyl)phenyl)-2-chloroacetamide (8f) and N-(3,5-bis(trifluoromethyl)phenyl)-2,2,3,3,3-pentafluoropropanamide (8h) were most active against 1st stage Ae. aegypti larvae with LC₅₀ values of 125 and 2.53 μM; for comparative purposes, the published LC₅₀ for fipronil is 0.014 μM. Compound 8h was the most toxic against adult female Ae. aegypti with an LD₅₀ = 2.12 nmol/mg, followed by 8f, and N-(3,5-bis(trifluoromethyl)phenyl)-2,2,2-trifluoroacetamide (8g) with LD₅₀ values of 4.27 and 4.73 nmol/mg, respectively, although these compounds were significantly less toxic than fipronil against adult female Ae. aegypti. Compounds N-(2-(trifluoromethyl)phenyl)butyramide (9c), N-(2-(trifluoromethyl)phenyl)pentanamide (9d) and N-(2-(trifluoromethyl)phenyl)hex-5-enamide (9e) were the best repellents for female Ae. aegypti, with minimum effective dosages (MEDs) of 0.026, 0.052, and 0.091 μmol/cm²_, respectively, compared to DEET at 0.052 μmol/cm². Out of 52 TFMPAs (total number of compounds from three generations of this research) compound 9c was the most active repellent along with two synthesized in our previous studies, 2-chloro-N-(3-(trifluoromethyl)phenyl)acetamide (6a) and 2,2,2-trifluoro-N-(2-(trifluoromethyl)phenyl)acetamide (4c).

Fungicidal Properties of Some Novel Trifluoromethylphenyl Amides

Trifluoromethylphenyl amides (TFMPAs) were designed and synthesized as potential pesticides. Thirty-three structures were evaluated for fungicidal activity against three Colletotrichum species using direct bioautography assays. Active compounds were subsequently tested against C. fragariae, C. gloeosporioides, C. acutatum, Phomopsis obscurans, P. viticola, Botrytis cinerea and Fusarium oxysporum. The study identified 2-chloro-N-[2,6-dichloro-4-(trifluoromethyl)phenyl]acetamide (7a) as showing the strongest antifungal activity, and the broadest activity spectrum in this set against Colletotrichum acutatum (at 48 and 72 h) and Phomopsis viticola (at 144 h). The presence of triethylamine in its complex with N-[2,6-dichloro-4-(trifluoromethyl)phenyl]-2,2,3,3,3-pentafluoropropanamide (7b') played an important role in the bioactivity, and depending on the concentration or fungal species it showed higher or lower activity than the parent amide. X-Ray crystallography has shown that the complex (7b') is an ion pair, (C₁₀ H₂ Cl₂ F₈ NO)^- (C₆ H₁₆ N)⁺ , where a proton is transferred from the amide nitrogen to the triethylamine nitrogen and then connected by hydrogen bonding to the acyl oxygen (N-H 0.893 Å; H⋅⋅⋅O 1.850 Å; N⋅⋅⋅O 2.711 Å; N-H⋅⋅⋅O 161.2(13)°). Although none of these compounds were better than standards, this work revealed some potential lead structures for further development of active novel compounds.

Visualizing Efficacy of Pesticides Against Disease Vector Mosquitoes in the Field

Efficacy of public health pesticides targeting nuisance and disease-vector insects such as mosquitoes, sand flies, and filth-breeding flies is not uniform across ecological zones. To best protect public and veterinary health from these insects, the environmental limitations of pesticides need to be investigated to inform effective use of the most appropriate pesticide formulations and techniques. We have developed a research program to evaluate combinations of pesticides, pesticide application equipment, and application techniques in hot-arid desert, hot-humid tropical, warm and cool temperate, and urban locations to derive pesticide use guidelines specific to target insect and environment. To these ends we designed a system of protocols to support efficient, cost-effective, portable, and standardized evaluation of a diverse range of pesticides and equipment across multiple environments. At the core of these protocols is the use of an array of small cages with colony-reared sentinel mosquitoes (adults and immatures) and sand flies (adults), strategically arranged in natural habitats and exposed to pesticide spray. Spatial and temporal patterns of pesticide efficacy are derived from percent mortality in sentinel cages, then mapped and visualized in a geographic information system. Maps of sentinel mortality data may be statistically compared to evaluate relative efficacy of a pesticide across multiple environments, or to study multiple pesticides in a single environment. Protocols may be modified to accommodate a variety of scenarios, including, for example, the vertical orientation of sentinels in canopy habitats or simultaneous testing of ground and aerial application methods.

Insecticidal and repellent properties of novel trifluoromethylphenyl amides II

This project focused on the design, synthesis, and testing of trifluoromethylphenyl amides (TFMPAs) as potential mosquitocides and repellents. Fourteen compounds were evaluated for toxicity against larvae and adults of Aedes aegypti. Several compounds were toxic against Aedes aegypti (larval, adult and feeding bioassays) and Drosophila melanogaster (glass-surface contact assay), but were much less toxic than fipronil, with toxicity ratios ranging from 100-fold in the larval assay to 100,000-fold for topical application to adult insects. In repellency bioassays to determine minimum effective dosage (MED), compound N-(2,6-dichloro-4-(trifluoromethyl)phenyl)-2,2,3,3,3-pentafluoropropanamide (7b) repelled Ae. aegypti females at lower concentration, 0.017 (±0.006) μmol/cm², than N, N-diethyl-meta-toluamide (DEET) 0.026 (±0.005) μmol/cm². 2-Chloro-N-(3-(trifluoromethyl)phenyl)acetamide (6a) performed better than DEET against two species of mosquitoes: it repelled Ae. aegypti females at 0.013 (±0.006) μmol/cm² and Anopheles gambiae females (in a warm body repellent assay), at a standard exposure of 2 nmol/cm². These studies revealed novel active structures that could further lead to compounds with better repellent activity.

Portable Battery Power and Small-Reservoir Modifications For Pesticide Misting Systems

United States military personnel deployed in austere hot-arid, temperate, and tropical conditions in remote locations worldwide rely on the Department of Defense (DoD) Pest Management System measures such as application of pesticide residual and ultra-low-volume or thermal fog treatments for protection from routine exposure to nuisance and disease-vector insects. Timed pesticide misting systems originally developed for residential outdoor use show promise as potential enhancements to standard DoD Pest Management System measures, in particular to protect perimeters surrounding US military field encampments. To investigate the capabilities of misting systems in remote locations in diverse environments, this technical engineering report describes the development of 2 key modifications to a commercial residential misting system to enable us to operate the system away from a standard power grid, and to safely operate the system with small volumes of a variety of pesticide misting formulations. The components needed to modify the commercial misting system include the following: 5,000-W inverter, 12-V 100 Ah battery, 24-gal tote, solar panel with charge controller, 18 in. (45.7 cm) 0-gauge wire with ½-in. (1.27-cm) eyebolt connectors, 5-gal container (wide mouthed), ½-in.-to-½-in. connector, ½-in. tubing, ⅜-in.-to-⅜-in. connector, ⅜-in. tubing, ¼-in.-to-¼-in. connector, ¼-in. flexible tubing, securable patio box (80 gal), 5-gal (18.9-liter) bucket (modified), and a canning funnel.

Residual Pesticide On Hesco® Blast Protection Wall In Temperate Florida Habitat Effective Against Mosquitoes, Stable Flies, and Sand Flies

United States military troops in the field are exposed to the environment and are thus at high risk for transmission of arboviruses, and degradation of mission from continual harassment from insects. Passive vector control, such as application of residual insecticides to US military materials common in the field such as tents and camouflage netting, has been shown to be effective and can contribute to a successful integrated vector management (IVM) plan in the field to reduce this risk. However, other common US military field materials have not been evaluated with residual pesticides. In this study we conducted the first known investigation of the efficacy and longevity of a residual pesticide containing λ-cyhalothrin applied to HESCO^® blast protection wall geotextile. We exposed treated material to a temperate Florida environment and found that this treatment can be effective against sand flies, filth-breeding flies, and mosquitoes for at least 6 wk. This study provides evidence that residual treatment of this US military material may be leveraged as an IVM component to enhance the US Department of Defense pest management system.

Ultra-Low Volume Application of Spinosad (Natular 2EC) as a Residual in a Hot-Arid Environment Against Aedes aegypti

The invasive Aedes aegypti is an important disease vector increasing in frequency in hot-arid regions of the USA such as the Southwest. Within hot-arid surroundings this mosquito may be confined to peridomestic locations that tend to be cooler and humid, such as in lush, irrigated ornamental vegetation surrounding homes. However, to reach these habitat refugia, ultra-low volume (ULV) applications of insecticides targeting this mosquito must retain efficacy after being sprayed from the air or street where hot-arid conditions are prevalent. We investigated the efficacy of a biologically based larvicide, spinosad (Natular 2EC), applied as a ULV in a hot-arid environment targeting Aedes aegypti. We found that this pesticide is able to penetrate this environment and has the potential to act as a residual.

TRUCK-MOUNTED NATULAR 2EC (SPINOSAD) ULV RESIDUAL TREATMENT IN A SIMULATED URBAN ENVIRONMENT TO CONTROL AEDES AEGYPTI AND AEDES ALBOPICTUS IN NORTH FLORIDA

Preemptive treatment of dry habitats with an ultra-low volume (ULV) residual larvicide may be effective in an integrated vector management program to control populations of container-inhabiting Aedes mosquitoes, key vectors of Zika, dengue, and chikungunya viruses. We exposed dry, artificial containers placed in exposed and protected locations to Natular 2EC (spinosad) larvicide applied with a truck-mounted ULV sprayer in a simulated urban setting in North Florida, and later introduced water and Ae. aegypti or Ae. albopictus larvae to conduct bioassays. Up to 50% mortality was observed in bioassays, indicating further analysis of spinosad as a residual treatment application.

Ultra-Low Volume Application of Spinosad (Natular 2EC) Larvicide as a Residual in a Tropical Environment Against Aedes and Anopheles Species

We investigated the efficacy of a liquid larvicide, Natular 2EC® (spinosad), applied with ultra-low volume sprayer as a residual application during the dry season in southeastern Thailand against 4 medically important species-Aedes aegypti, Ae. albopictus, Anopheles dirus, and An. minimus. We found that this larvicide could be applied as a residual to dry areas known to collect water and potentially still be effective after rains or irrigation, which could increase the flexibility and efficiency of an integrated vector management program targeting these species. This investigation also demonstrated, for the 1st time, efficacy of spinosad against An. minimus and An. dirus.

Aerial ULV control of Aedes aegypti with naled (Dibrom) inside simulated rural village and urban cryptic habitats

We conducted aerial fixed wing ultra low volume (ULV) spray trials with naled to investigate penetration of exposed and simulated cryptic habitat within opened buildings, partially sealed buildings, and outdoor locations targeting sentinel adult Aedes aegypti mosquitoes in north central Florida. Mortality was observed in open and closed buildings and outdoors, even in mosquitoes placed in cryptic habitats. Observations on the impact of building type, mosquito exposure method such as placement in cryptic habitat, and spray nozzle size on mosquito mortality are described and analyzed.

African and Asian Zika Virus Isolates Display Phenotypic Differences Both In Vitro and In Vivo

Zika virus (ZIKV) is a mosquito-borne member of the genus Flavivirus that has emerged since 2007 to cause outbreaks in Africa, Asia, Oceania, and most recently, in the Americas. Here, we used an isolate history as well as genetic and phylogenetic analyses to characterize three low-passage isolates representing African (ArD 41525) and Asian (CPC-0740, SV0127-14) lineages to investigate the potential phenotypic differences in vitro and in vivo. The African isolate displayed a large plaque phenotype (∼3-4 mm) on Vero and HEK-293 cells, whereas the Asian isolates either exhibited a small plaque phenotype (∼1-2 mm) or did not produce any plaques. In multistep replication kinetics in nine different vertebrate and insect cell lines, the African isolate consistently displayed faster replication kinetics and yielded ∼10- to 10,000-fold higher peak virus titers (infectious or RNA copies) compared with the Asian isolates. Oral exposure of Aedes aegypti mosquitoes with the African isolate yielded higher infection and dissemination rates compared with the Asian isolates. Infection of Ifnar1^-/- mice with the African isolate produced a uniformly fatal disease, whereas infection with the Asian isolates produced either a delay in time-to-death or a significantly lower mortality rate. Last, the African isolate was > 10,000-fold more virulent than the Asian isolates in an interferon type I antibody blockade mouse model. These data demonstrate substantial phenotypic differences between low-passage African and Asian isolates both in vitro and in vivo and warrant further investigation. They also highlight the need for basic characterization of ZIKV isolates, as the utilization of the uncharacterized isolates could have consequences for animal model and therapeutic/vaccine development.

Limited impacts of truck-based ultra-low-volume applications of mosquito adulticides on mortality in honey bees (Apis mellifera)

Adulticides applied against mosquitoes can reduce vector populations during times of high arbovirus transmission. However, impacts of these insecticides on pollinators and other non-target organisms are of concern to mosquito control professionals, beekeepers and others. We evaluated mortality of Culex quinquefasciatus and Apis mellifera when caged insects were exposed to low and high label rates of four common adulticides (Aqua-Pursuit™ [permethrin], Duet® [prallethrin + sumithrin], Fyfanon® [malathion] and Scourge® [resmethrin]) at six distances up to 91.4 m from a truck-mounted ultra-low-volume sprayer. Honey bee mortality was both absolutely low (61 m had limited impacts on honey bee mortality while providing effective mosquito control.

Application Site and Mosquito Age Influences Malathion- and Permethrin-Induced Mortality in Culex quinquefasciatus (Diptera: Culicidae)

Concentrations of malathion and permethrin typical in droplets generated from ultra-low-volume and low-volume applications used to control mosquito populations were evaluated for efficacy against multiple-aged Culex quinquefasciatus Say (Diptera: Culicidae), using a topical bioassay. Although insecticide droplets will impinge on many exoskeletal body regions and a range of ages of mosquitoes in a population, traditional mosquito topical bioassays focus pesticide application to the mesothoracic pleural or dorsal regions across an average mosquito age (e.g., 3-7 d). Our results document nonuniform insecticide sensitivity across body regions at ages not previously assessed in mosquitoes (teneral and 14-d old). We expect our findings to influence the topical bioassay process, illustrating the difference in mosquito body regions and ages that ultimately may explain insecticide effectiveness wherever droplets impinge upon the mosquito body during field control applications.

Permethrin and malathion LD90 values for Culex quinquefasciatus vary with topical application site

Prior research in multiple insect species has demonstrated that insecticide-induced mortality varies according to the body region exposed on the insect. This variation has been demonstrated in Culex quinquefasciatus Say (Diptera: Culicidae), but has not been quantified using dose-response curves. Applications of technical permethrin or malathion to one of three body regions on Cx. quinquefasciatus resulted in dose-response curves that were not equivalent to one another. The generated LD₉₀ values and curves for each body region were compared with previously reported LD values for analogous sites in several mosquito species, specifically the mesothorax. Based on the present results, the permethrin and malathion LD₅₀ and LD₉₀ concentrations required for droplets impinging on the abdomen and mesothorax of Cx. quinquefasciatus when applied through ground-based spray systems utilized by mosquito control programmes were calculated.

Field Evaluation of Indoor Thermal Fog and Ultra-Low Volume Applications For Control of Aedes aegypti in Thailand

Efficacies of a handheld thermal fogger (Patriot™) and a backpack ultra-low volume (ULV) sprayer (Twister™) with combinations of 2 different adulticides (pyrethrin, deltamethrin) and an insect growth regulator (pyriproxyfen) were field-tested and compared for their impact on reducing indoor Aedes aegypti populations in Thailand. The effectiveness of the indoor space sprays was evaluated by sampling the natural Ae. aegypti population in houses and determining their physiological status, by monitoring mortality of sentinel caged mosquitoes (AFRIMS strain) and by assessing larval mortality in laboratory bioassays using water exposed to the spray. A total of 14,742 Ae. aegypti were collected from Biogents Sentinel traps in this study. The combination of ULD® BP-300 (3% pyrethrin) and NyGuard® (10% pyriproxyfen) sprayed either by the Patriot or Twister significantly reduced some Ae. aegypti populations up to 20 days postspray relative to the control clusters. The addition of pyriproxyfen to the adulticide extended how long household mosquito populations were suppressed. In 2 of the 4 products being compared, the Twister resulted in higher mortality of caged mosquitoes compared with the Patriot. However, neither machine was able to achieve high mortality among Ae. aegypti placed in hidden (protected) cages. The larval bioassay results demonstrated that the Twister ULV provided better adult emergence inhibition than the Patriot (thermal fogger), likely due to larger droplet size.

Low potential for mechanical transmission of Ebola virus via house flies (Musca domestica)

BACKGROUND

Ebola virus (EBOV) infection results in high morbidity and mortality and is primarily transmitted in communities by contact with infectious bodily fluids. While clinical and experimental evidence indicates that EBOV is transmitted via mucosal exposure, the ability of non-biting muscid flies to mechanically transmit EBOV following exposure to the face had not been assessed.

RESULTS

To investigate this transmission route, house flies (Musca domestica Linnaeus) were used to deliver an EBOV/blood mixture to the ocular/nasal/oral facial mucosa of four cynomolgus macaques (Macaca fascicularis Raffles). Following exposure, macaques were monitored for evidence of infection through the conclusion of the study, days 57 and 58. We found no evidence of systemic infection in any of the exposed macaques.

CONCLUSIONS

The results of this study indicate that there is a low potential for the mechanical transmission of EBOV via house flies - the conditions in this study were not sufficient to initiate infection.

Epidemiologic and Environmental Risk Factors of Rift Valley Fever in Southern Africa from 2008 to 2011

Background: Rift Valley fever (RVF) outbreaks have been associated with periods of widespread and above-normal rainfall over several months. Knowledge on the environmental factors influencing disease transmission dynamics has provided the basis for developing models to predict RVF outbreaks in Africa. From 2008 to 2011, South Africa experienced the worst wave of RVF outbreaks in almost 40 years. We investigated rainfall-associated environmental factors in southern Africa preceding these outbreaks.

Methods: RVF epizootic records obtained from the World Animal Health Information Database (WAHID), documenting livestock species affected, location, and time, were analyzed. Environmental variables including rainfall and satellite-derived normalized difference vegetation index (NDVI) data were collected and assessed in outbreak regions to understand the underlying drivers of the outbreaks.

Results: The predominant domestic vertebrate species affected in 2008 and 2009 were cattle, when outbreaks were concentrated in the eastern provinces of South Africa. In 2010 and 2011, outbreaks occurred in the interior and southern provinces affecting over 16,000 sheep. The highest number of cases occurred between January and April but epidemics occurred in different regions every year, moving from the northeast of South Africa toward the southwest with each progressing year. The outbreaks showed a pattern of increased rainfall preceding epizootics ranging from 9 to 152 days; however, NDVI and rainfall were less correlated with the start of the outbreaks than has been observed in eastern Africa.

Conclusions: Analyses of the multiyear RVF outbreaks of 2008 to 2011 in South Africa indicated that rainfall, NDVI, and other environmental and geographical factors, such as land use, drainage, and topography, play a role in disease emergence. Current and future investigations into these factors will be able to contribute to improving spatial accuracy of models to map risk areas, allowing adequate time for preparation and prevention before an outbreak occurs.

Impact of Topical Application Site On the Efficacy of Permethrin and Malathion To Culex quinquefasciatus

Although insecticide spray droplets will potentially impinge on many exoskeletal body regions, traditional mosquito topical bioassays focus insecticide application to the mesothoracic pleural or dorsal area. Concentrations of permethrin and malathion found in droplets from ultra-low volume and low-volume sprays were evaluated for efficacy against adult Culex quinquefasciatus using a topical application bioassay. Results document nonuniform insecticide sensitivity across body regions, which has not been previously assessed in mosquitoes. Insecticide contact with appendages, such as the leg and the wing, returned much lower mortality from both insecticides than exposure to the primary body (i.e., head, thorax, and abdomen). No difference was observed in percent mortality 24 h after exposure to different insecticides to the same body region. Sublethal behaviors were also observed and discussed for both insecticides. Our findings provide valuable information for those performing topical bioassays, and may help explain insecticide effectiveness wherever droplets impinge upon the mosquito body during laboratory or field applications.