Acoustic Control of Mosquito Larvae In Artificial Drinking Water Containers.

Emerging technology designed to kill mosquito larvae with sound waves may present a nonchemical and nonbiological alternative to reduce larval populations of key medically important mosquito species such as Aedes aegypti in containers or catchments of water. These devices could benefit integrated vector management programs facing public resistance to the use of chemical or biological larvicides in stored drinking water. In this study we investigate the efficacy of a Larvasonic SD-Mini Acoustic Larvicide device in reducing larval populations of Ae. aegypti in 3 volumes of water across a range of acoustic exposure durations. We report lethal pulse duration times for 50% and 90% mortality and optimal exposure durations for the tested water volumes.

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.

Comparison of Volatiles and Mosquito Capture Efficacy For Three Carbohydrate Sources In A Yeast-Fermentation CO2 Generator.

Mosquito surveillance in remote areas with limited access to canisters of CO2 or dry ice will benefit from an effective alternative CO2 source, such as the natural production of CO2 from yeast fermentation. In this study, we investigate differences in mosquito capture rates from the Centers for Disease Control and Prevention (CDC) light traps baited with dry ice compared with traps baited with yeast fermentation of several carbohydrate sources over 23 trap-nights. Results demonstrated the ability of yeast-generated CO2 to effectively attract mosquitoes to a CDC trap, regardless of carbohydrate source. Total collections of mosquitoes using dry ice were significantly higher than collections from yeast-generated CO2 sources. However, mosquito community structure, i.e., the species and relative capture rate of each species, was represented comparably across collections regardless of CO2 source. Volatiles produced by yeast fermentation were analyzed by carbohydrate source, revealing a suite of compounds, possibly synergistic, enhancing effects with CO2 on mosquito collection capability compared with the amount of CO2 used to attract mosquitoes.

Potential for Psorophora columbiae and Psorophora ciliata Mosquitoes (Diptera: Culicidae) to Transmit Rift Valley Fever Virus.

Rift Valley fever virus (RVFV) continues to pose a threat to much of the world. Unlike many arboviruses, numerous mosquito species have been associated with RVFV in nature, and many species have been demonstrated as competent vectors in the laboratory. In this study, we evaluated two field-collected Psorophora species, Psorophora columbiae (Dyar and Knab) and Psorophora ciliata (F.) for their potential to transmit RVFV in North America. Both species were susceptible to infection after feeding on a hamster with a viremia of 10(7) plaque-forming units/ml, with infection rates of 65 and 83% for Ps. columbiae and Ps. ciliata, respectively (with nearly all specimens becoming infected when feeding on a hamster with a higher viremia). However, both species had a significant salivary gland barrier, as only 2/35 Ps. columbiae and 0/3 Ps. ciliata with a disseminated infection transmitted virus by bite. Despite the presence of the salivary gland barrier, due to the very high population that can occur and its propensity to feed on large mammals, Ps. columbiae might play a role in amplifying RVFV should that virus be introduced into an area where this species is common.

Passive Baited Sequential Filth Fly Trap.

Filth fly control measures may be optimized with a better understanding of fly population dynamics measured throughout the day. We describe the modification of a commercial motorized sequential mosquito trap to accept liquid odorous bait and leverage a classic inverted-cone design to passively confine flies in 8 modified collection bottles corresponding to 8 intervals. Efficacy trials in a hot-arid desert environment indicate no significant difference (P  =  0.896) between the modified sequential trap and a Rid-Max® fly trap.

A mobile app for military operational entomology pesticide applications.

Multiple field studies conducted for the Deployed War-Fighter Protection (DWFP) research program have generated more than 80 specific guidance points for innovative combinations of pesticide application equipment, pesticide formulations, and application techniques for aerosol and residual pesticide treatments in 6 ecological regions against a range of mosquito, sand fly, and filth fly nuisance and disease-vector threats. To synthesize and operationalize these DWFP field and laboratory efficacy data we developed an interactive iOS and Android mobile software application, the Pesticide App, consisting of specific pesticide application guidance organized by environment and target insect vector species.

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).

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.

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.

Gamma-Irradiated Female Aedes aegypti Mosquitoes Exhibit Greater Susceptibility to Mayaro Virus.

Mayaro virus (MAYV) is an alphavirus endemic in many parts of Central and South America transmitted to humans by Aedes aegypti. Currently, there is no vaccine or treatment of Mayaro infection, and therefore it is essential to control transmission by reducing populations of Ae. aegypti. Unfortunately, Ae. aegypti are extremely difficult to control with traditional integrated vector management (IVM) because of factors such as growing resistance to a dwindling list of registered insecticides and cryptic immature and adult habitats. The sterile insect technique (SIT) by irradiation is gaining traction as a novel supplemental tool to IVM. The SIT is being used operationally to release large numbers of sterilized colony-reared male mosquitoes in an intervention area to overwhelm females in the natural population, eventually causing population decline because of high frequencies of unfertilized eggs. However, little is known about the effect of irradiation on vector competence for mosquito-borne viruses such as MAYV in females that may be accidentally reared, irradiated, and released alongside males. In this investigation, we exposed female Ae. aegypti pupae to radiation and evaluated vector competence after inoculation with MAYV. Infection and dissemination rates of irradiated (10 and 40 Gy) Ae. aegypti were higher than those of non-irradiated cohorts at 7 and 14 days after infection. Although these results indicate a need to maintain effective sex sorting prior to irradiation and release of Ae. aegypti, our results are consistent with several previous observations that vectorial capacity and vector competence are likely lower in irradiated than in nonirradiated females.

Potential for mosquitoes (Diptera: Culicidae) from Florida to transmit Rift Valley fever virus.

We evaluated Aedes atlanticus Dyar and Knab, Aedes infirmatus Dyar and Knab, Aedes vexans (Meigen), Anopheles crucians Wiedemann, Coquillettidia perturbans (Walker), Culex nigripalpus Theobald, Mansonia dyari Belkin, Heinemann, and Page, and Psorophora ferox (Von Humboldt) from Florida to determine which of these species should be targeted for control should Rift Valley fever virus (RVFV) be detected in North America. Female mosquitoes that had fed on adult hamsters inoculated with RVFV were incubated for 7-21 d at 26 degrees C, then allowed to refeed on susceptible hamsters, and tested to determine infection, dissemination, and transmission rates. We also inoculated mosquitoes intrathoracically, held them for 7 d, and then allowed them to feed on a susceptible hamster to check for a salivary gland barrier. When exposed to hamsters with viremias > or = 10(7.6) plaque-forming units per milliliter of blood, at least some individuals in each of the species tested became infected; however, Cx. nigripalpus, An. crucians, and Ae. infirmatus were essentially incompetent vectors in the laboratory because of either a midgut escape or salivary gland barrier. Each of the other species should be considered as potential vectors and would need to be controlled if RVFV were introduced into an area where they were found. Additional studies need to be conducted with other geographic populations of these species and to determine how environmental factors affect transmission.

High-throughput mosquito and fly bioassay system for natural and artificial substrates treated with residual insecticides.

A high-throughput bioassay system to evaluate the efficacy of residual pesticides against mosquitoes and muscid flies with minimal insect handling was developed. The system consisted of 4 components made of readily available materials: 1) a CO2 anaesthetizing chamber, 2) a specialized aspirator, 3) a cylindrical flat-bottomed glass bioassay chamber assembly, and 4) a customized rack.

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.

Aspirator gun for high-throughput mosquito bioassays.

We describe an innovative aspirator gun designed to transfer individual anesthetized mosquitoes directly into glass bioassay tubes. The gun has been used for thousands of transfers with extremely low associated mortality and is the central component of a high-throughput bioassay system. The gun is constructed using readily obtainable materials and can be modified for a range of insects.

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.

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.

Longevity and efficacy of bifenthrin treatment on desert-pattern US military camouflage netting against mosquitoes in a hot-arid environment.

The current Department of Defense pest management system does not provide adequate protection from arthropod disease vectors to personnel deployed in support of US military operations. We hypothesized that military camouflage netting, ubiquitous around living and working areas in current US military operations in Africa and the Middle East, treated with a residual pesticide such as bifenthrin may reduce the presence of biting insects and improve the military pest management system. In this study, we examined the longevity and efficacy of bifenthrin applied to camouflage netting material at the maximum label rate of 0.03 liter formulation (7.9% AI) per 92.9 m2 against field populations of mosquitoes in southern California in a hot-arid environment similar to regions of Iraq, Afghanistan, and the Horn of Africa. We showed that bifenthrin treatment of camouflage netting was effective at reducing mosquito populations, predominantly Psorophora columbiae and Aedes vexans, by an average of up to 46% for 56 days, and could cause as much as 40% mortality in Culex quinquefasciatus in laboratory bioassays for nearly 2 months postapplication. These population reductions could translate to commensurate reductions in risk of exposure to mosquito-borne pathogens, and could potentially be effective against sand flies and filth flies.

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.