Explore the vast range of titles available.

The bed bug (Cimex lectularius L.) is one of the most prolific and burdensome indoor pests, and suppression of bed bug populations is a global priority. Understanding bed bug behavior is important to the development of new tactics for their control. Major gaps exist in our understanding of how host cues, insecticide resistance, and exposure modality impact the repellency of formulated products to bed bugs. Here, we validate the use of a binary choice olfactometer for assessing bed bug repellency behaviors using N,N-diethyl-3-methylbenzamide (DEET) in a dose-dependent manner, while considering the role of host-associated stimuli (with vs. without CO2), exposure modality (olfactory vs. olfactory and contact), and resistance status (susceptible vs. resistant) on repellency. We observed that host-seeking insecticide-susceptible bed bugs were repelled only when olfactorily exposed to high concentrations of DEET. However, exposure to DEET by contact repelled insecticide-susceptible bed bugs at 100-fold lower dose of DEET. Further, we demonstrate for the first time that insecticide-resistant bed bugs were significantly more responsive to DEET than susceptible bed bugs. We conclude that the 2-choice olfactometer is an effective tool for assessing the behavioral responses of bed bugs to spatial and contact repellents.

Rapidly increasing pyrethroid insecticide resistance and changes in vector biting and resting behavior pose serious challenges in malaria control. Mosquito repellents, especially spatial repellents, have received much attention from industry. We attempted to simulate interactions between mosquitoes and repellents using a machine learning method, the Self-Propelled Particle (SPP) model, which we modified to include attractiveness/repellency effects. We simulated a random walk scenario and scenarios with insecticide susceptible/resistant mosquitoes against repellent alone and against repellent plus attractant (to mimic a human host). Simulation results indicated that without attractant/repellent, mosquitoes would fly anywhere in the cage at random. With attractant, all mosquitoes were attracted to the source of the odor by the end. With repellent, all insecticide-susceptible mosquitoes eventually moved to the corner of the cage farthest from the repellent release point, whereas, a high proportion of highly resistant mosquitoes might reach the attractant release point (the human) earlier in the simulation. At fixed concentration, a high proportion of mosquitoes could be able to reach the host when the relative repellency efficacy (compare to attractant efficacy) was <1, whereas, no mosquitoes reached the host when the relative repellency efficacy was > 1. This result implies that repellent may not be sufficient against highly physiologically insecticide resistant mosquitoes, since very high concentrations of repellent are neither practically feasible nor cost-effective.

In southern Zambia, malaria transmission is low, with outdoor biting Anopheles mosquitoes playing a significant role in malaria transmission. Locals cook in outdoor, open-walled kitchen shelters, exposing them to these outdoor biting vectors and malaria. Volatile pyrethroid spatial emanators (SE) operate through a mode of action which could provide local protection around these kitchens. In this study, SE devices containing the pyrethroid transfluthrin were deployed to local kitchens, where human landing collection (HLC) was utilized to determine differences in host-landing rates associated with protection. Forty-one households from two villages were enrolled in the study in clusters of five (or six) and randomly assigned a treatment by cluster. Local mosquito collectors were recruited and trained to conduct HLCs from 18:00-06:00 once per week for 15 weeks. SE and placebo devices were replaced monthly. Following collection, mosquitoes were returned to the lab for morphological identification. Results were analyzed in R with negative binomial generalized linear mixed models (GLMM) considering all-night and per-hour capture. A total of 3021 mosquitoes were collected during the follow-up period, with Anopheles species composing roughly half of all specimens. Anopheles activity was lower in SE protected kitchens based on all night and hourly comparisons. Mosquito activity was highest in the middle of the night, and SE was not significantly associated with protection between 18:00-21:00. SE usage appeared to reduce mosquito host-seeking activity by approximately 65-70%, with this efficacy appearing to diminish gradually over time to approximately 20-25% four weeks after opening, at which point they were replaced. Culicine mosquito behavior was not significantly impacted by the SE. The SE device provided protection to individuals within protected kitchen structures overnight and during most hours of the night. The number of mosquitoes was lowest during the early collection hours between 18:00-21:00, a period in which the SE devices did not significantly impact mosquito host-seeking behavior. This result has implications for this use-case and should be further explored.

Understanding the interactions between increased insecticide resistance and resting behaviour patterns of malaria mosquitoes is important for planning of adequate vector control. This study was designed to investigate the resting behavior, host preference and rates of Plasmodium falciparum infection in relation to insecticide resistance of malaria vectors in different ecologies of western Kenya. Anopheles mosquito collections were carried out during the dry and rainy seasons in Kisian (lowland site) and Bungoma (highland site), both in western Kenya using pyrethrum spray catches (PSC), mechanical aspiration (Prokopack) for indoor collections, clay pots, pit shelter and Prokopack for outdoor collections. WHO tube bioassay was used to determine levels of phenotypic resistance of indoor and outdoor collected mosquitoes to deltamethrin. PCR-based molecular diagnostics were used for mosquito speciation, genotype for knockdown resistance mutations (1014S and 1014F) and to determine specific host blood meal origins. Enzyme-linked Immunosorbent Assay (ELISA) was used to determine mosquito sporozoite infections. Anopheles gambiae s.l. was the most predominant species (75%, n = 2706) followed by An. funestus s.l. (25%, n = 860). An. gambiae s.s hereafter (An. gambiae) accounted for 91% (95% CI: 89-93) and An. arabiensis 8% (95% CI: 6-9) in Bungoma, while in Kisian, An. arabiensis composition was 60% (95% CI: 55-66) and An. gambiae 39% (95% CI: 34-44). The resting densities of An. gambiae s.l and An. funestus were higher indoors than outdoor in both sites (An. gambiae s.l; F1, 655 = 41.928, p < 0.0001, An. funestus; F1, 655 = 36.555, p < 0.0001). The mortality rate for indoor and outdoor resting An. gambiae s.l F1 progeny was 37% (95% CI: 34-39) vs 67% (95% CI: 62-69) respectively in Bungoma. In Kisian, the mortality rate was 67% (95% CI: 61-73) vs 76% (95% CI: 71-80) respectively. The mortality rate for F1 progeny of An. funestus resting indoors in Bungoma was 32% (95% CI: 28-35). The 1014S mutation was only detected in indoor resitng An. arabiensis. Similarly, the 1014F mutation was present only in indoor resting An. gambiae. The sporozoite rates were highest in An. funestus followed by An. gambiae, and An. arabiensis resting indoors at 11% (34/311), 8% (47/618) and 4% (1/27) respectively in Bungoma. Overall, in Bungoma, the sporozoite rate for indoor resting mosquitoes was 9% (82/956) and 4% (8/190) for outdoors. In Kisian, the sporozoite rate was 1% (1/112) for indoor resting An. gambiae. None of the outdoor collected mosquitoes in Kisian tested positive for sporozoite infections (n = 73). The study reports high indoor resting densities of An. gambiae and An. funestus, insecticide resistance, and persistence of malaria transmission indoors regardless of the use of long-lasting insecticidal nets (LLINs). These findings underline the difficulties of controlling malaria vectors resting and biting indoors using the current interventions. Supplemental vector control tools and implementation of sustainable insecticide resistance management strategies are needed in western Kenya.

West Nile virus (WNV) is the leading mosquito-borne disease causing-pathogen in the United States. Concerningly, there are no prophylactics or drug treatments for WNV and public health programs rely heavily on vector control efforts to lessen disease incidence. Insecticides can be effective in reducing vector numbers if implemented strategically, but can diminish in efficacy and promote insecticide resistance otherwise. Vector control programs which employ mass-fogging applications of insecticides, often conduct these methods during the late-night hours, when diel temperatures are coldest, and without a-priori knowledge on daily mosquito activity patterns. This study’s aims were to 1) quantify the effect of temperature on the toxicity of two conventional insecticides used in fogging applications (malathion and deltamethrin) to Culex tarsalis , an important WNV vector, and 2) quantify the time of host-seeking of Cx . tarsalis and other local mosquito species in Maricopa County, Arizona. The temperature-toxicity relationship of insecticides was assessed using the WHO tube bioassay, and adult Cx . tarsalis , collected as larvae, were exposed to three different insecticide doses at three temperature regimes (15, 25, and 35°C; 80% RH). Time of host-seeking was assessed using collection bottle rotators with encephalitis vector survey traps baited with dry ice, first at 3h intervals during a full day, followed by 1h intervals during the night-time. Malathion became less toxic at cooler temperatures at all doses, while deltamethrin was less toxic at cooler temperatures at the low dose. Regarding time of host-seeking, Cx . tarsalis , Aedes vexans , and Culex quinquefasciatus were the most abundant vectors captured. During the 3-hour interval surveillance over a full day, Cx . tarsalis were most-active during post-midnight biting (00:00–06:00), accounting for 69.0% of all Cx . tarsalis , while pre-midnight biting (18:00–24:00) accounted for 30.0% of Cx . tarsalis . During the 1-hour interval surveillance overnight, Cx . tarsalis were most-active during pre-midnight hours (18:00–24:00), accounting for 50.2% of Cx . tarsalis captures, while post-midnight biting (00:00–06:00) accounted for 49.8% of Cx . tarsalis . Our results suggest that programs employing large-scale applications of insecticidal fogging should consider temperature-toxicity relationships coupled with time of host-seeking data to maximize the efficacy of vector control interventions in reducing mosquito-borne disease burden.

Background Interventions against adult Anopheles mosquitoes responsible for malaria transmission have traditionally been aimed at indoor spaces and biting behaviours. However, no globally recommended intervention exists which directly interrupt or target outdoor biting behaviours. A volatile pyrethroid spatial emanator (SE) containing transfluthrin aims to address this gap in protection via a simple-to-use, readily deployable device to provide multiple weeks of protection. The device was tested in open-walled households of the forest-dwelling Orang Rimba people in Sumatra, Indonesia, over the course of sixteen weekly entomological visits. Methods Double-net traps were used for all mosquito collections. Collections occurred near Bukit Duabelas National Park in central Sumatra, an area characterized by secondary forests undergoing widespread conversion to palm and rubber plantations. Four collections occurred per collection night within ten geographically separated small familial groups for a total of 40 trap-nights per week. Groups were assigned the SE or a control device after a seven-week baseline trapping period. Devices were replaced every four weeks. Results were compared using generalized linear models, incorporating treatment, weather, and landscape parameters as fixed effects, with date and location included as random effects. Results Anopheles mosquitoes were captured on 63.2% of all collection nights. Overall nightly Anopheles host-seeking activity was lower in the presence of SE devices (RR: 0.29 [0.19–0.45], p  < 0.001). Non- Anopheles mosquitoes experienced a smaller nightly decline in behaviour (RR: 0.78 [0.64–0.93], p  = 0.007). The age of the device (1 month) did not impact modeled efficacy. Anopheles host-seeking activity was also positively correlated with humidity, topographic wetness, and local human structure density. Conclusions The SE device evaluated in this field trial was effective in reducing outdoor human exposure to Anopheles and non- Anopheles mosquito host-seeking activity. The effect was not found to depend upon the age of the device, suggesting that the protection was persistent over the 4-week replacement period during this study. There was an association between hour of collection and intervention efficacy, suggesting the possibility of species-specific effects which were not further investigated. The SE device is a promising, low-cost, easily deployable, and distributable intervention that reduces exposure to mosquitoes with consequent impacts on transmission in outdoor environments.

Host seeking in the yellow fever mosquito, Aedes aegypti, and the African malaria mosquito, Anopheles coluzzii, relies on specific and generic host-derived odorants. Previous analyses indicate that the behavioral response of these species depends differentially on the presence of carbon dioxide (CO2) and other constituents in human breath for activation and attraction. In this study, we use a flight tube assay and electrophysiological analysis to assess the role of acetone, a major component of exhaled human breath, in modulating the behavioral and sensory neuronal response of these mosquito species, in the presence and absence of CO2. When presented alone at ecologically relevant concentrations, acetone increases attraction in Ae. aegypti, but not in An. coluzzii. Moreover, in combination with CO2, human breath-equivalents of acetone ranging between 0.1 and 10 ppm reproduces a behavioral response similar to that observed to human breath in host-seeking Ae. aegypti, but not in An. coluzzii. Acetone does, however, reduce attraction to CO2 in An. coluzzii, when presented at a higher concentration of 10 ppm. We identify the capitate peg A neuron of the maxillary palp of both species as a dual detector of CO2 and acetone. The sensory response to acetone, or binary blends of acetone and CO2, reflects the observed behavioral output in both Ae. aegypti and An. coluzzii. We conclude that host recognition is contextual and dependent on a combination of ecologically relevant odorants at naturally occurring concentrations that are encoded, in this case, by differences in the temporal structure of the neuronal response. This information should be considered when designing synthetic blends for that optimally attract mosquitoes for monitoring and control.

The deployment of odor-baited tools for sampling and controlling malaria vectors is limited by a lack of potent synthetic mosquito attractants. A synthetic mixture of chemical compounds referred to as “the Mbita blend” (MB) was shown to attract as many host-seeking malaria mosquitoes as attracted to human subjects. We hypothesized that this effect could be enhanced by adding one or more attractive compounds to the blend. We tested changes in the capability of MB (ammonia + L-lactic acid + tetradecanoic acid +3-methyl-1-butanol + carbon dioxide) to attract host-seeking malaria mosquitoes by addition of selected dilutions of butyl-2-methylbutanoate (1:10,000), 2-pentadecanone (1:100), 1-dodecanol (1:10,000), and butan-1-amine (1:10,000,000). The experiments were conducted in semi-field enclosures and in a village in western Kenya. In semi-field enclosures, the attraction of Anopheles gambiae sensu stricto females to MB-baited traps was not enhanced by adding butyl-2-methylbutanoate. There was, however, an increase in the proportion of An. gambiae caught in traps containing MB augmented with the selected dilutions of butan-1-amine, 2-pentadecanone, and 1-dodecanol. When tested in the village, addition of butan-1-amine to MB enhanced catches of female An. gambiae sensu lato , An. funestus , and Culex mosquitoes. 1-Dodecanol increased attraction of An. gambiae s.l. to the MB, while addition of 2-pentadecanone improved trap catches of An. funestus and Culex mosquitoes. This study demonstrates the possibility of enhancing synthetic odor blends for trapping the malarial mosquitoes An. gambiae s.l. and An. funestus , as well as some culicine species. The findings provide promising results for the optimization and utilization of synthetic attractants for sampling and controlling major disease vectors.

Trichogramma chilonis Ishii is an important natural enemy of many lepidopterous pests on various crops. Effects of two conventional insecticides on oviposition and host discrimination behavior in T. chilonis were evaluated in the laboratory through video tracking. During the oviposition period, when the number of host eggs was limited (only one host egg), females exposed to beta-cypermethrin LC1 or LC20 exhibited significantly higher feeding and re-drilling rate and significantly longer post-oviposition duration than control females. Spinosad LC20 treatment not only decreased the wasp oviposition rate but also significantly extended the oviposition duration. When the number of host eggs was six, similarly, females exposed to spinosad LC20 exhibited a significantly lower oviposition rate (79.2%) than control ones (100%). In the host discrimination experiment, females exposed to LC20 of both tested insecticides (beta-cypermethrin and spinosad) spent significantly more time on the extra-patch area. The females that survived spinosad LC20 could not discriminate between unparasitized and parasitized host eggs. Our study suggests that even the LC1 and LC20 of the tested insecticides had negative effects on the oviposition and host discrimination behavior of T. chilonis. Thus, the use of these two insecticides should be carefully evaluated.

The high vector competence of mosquitoes is intrinsically linked to their reproductive strategy because females need a vertebrate blood meal to develop large batches of eggs. However, the molecular mechanisms and pathways regulating mosquito host-seeking behaviour are largely unknown. Here, we test whether host-seeking behaviour may be linked to the female's energy reserves, with low energy levels triggering the search for a nutrient-rich blood meal. Our results demonstrate that sugar feeding delays host-seeking behaviour in the invasive tiger mosquito Aedes albopictus, but the levels of energy reserves do not correlate with changes in host-seeking behaviour. Using tissue-specific gene expression analyses, we show for the first time, to our knowledge, that sugar feeding alone induces a transient up-regulation of several vitellogenesis-related genes in the female fat body, resembling the transcriptional response after a blood meal. Specifically, high expression levels of a vitellogenin gene (Vg-2) correlated with the lowest host-seeking activity of sugar-fed females. Knocking down the Vg-2 gene via RNA interference (RNAi) restored host-seeking behaviour in these females, firmly establishing that Vg-2 gene expression has a pivotal role in regulating host-seeking behaviour in young Ae. albopictus females. The identification of a molecular mechanism regulating host-seeking behaviour in mosquitoes could pave the way for novel vector control strategies aiming to reduce the biting activity of mosquitoes. From an evolutionary perspective, this is the first demonstration of vitellogenin genes controlling feeding-related behaviours in nonsocial insects, while vitellogenins are known to regulate caste-specific foraging and brood-care behaviours in eusocial insects. Hence, this work confirms the key role of vitellogenin in controlling feeding-related behaviours in distantly related insect orders, suggesting that this function could be more ubiquitous than previously thought.