Synthetic insecticides have been used for a long time as one of the most effective tools for insect pest control. However, the re-emergence of insect pests and their fast development of resistance, as has occurred for pyrethroid-resistant bed bugs Cimex lectularius L., make it necessary to develop new and safe strategies for effective pest control. This has fostered the research on new eco-sustainable formulations based on essential oils, which allows reducing the impact associated with the intensive use of synthetic insecticides on the environment and their effects on human health. This research explores the stability of water/eugenol/ethanol surfactantless emulsions loaded with imidacloprid (0.003 wt%), and their toxicity against a resistant bed bug strain. The results have shown that these emulsions enable the solubilization of a poorly water-soluble drug, such as the imidacloprid, without any significant modification of their stability. Furthermore, the application of the obtained formulations against the pyrethroid-resistant bed bug results in mortality in the 50–85% range upon topical and spray applications, with the increase of the eugenol content enhancing the effectiveness of the formulations. It may be expected that the ternary water/eugenol/ethanol mixtures could be further developed in the preparation of ready to use formulations, enabling the dispersion of insecticides for pest control.

Immature mosquitoes are thought to breathe only atmospheric air through their siphons despite reports of prolonged submerged survival. We studied the survival of last-instar larvae of Aedes aegypti fully submerged at different temperatures and measured the oxygen consumption from air and water-dissolved larvae and pupae of this species under different conditions. Larvae survived much longer than expected, reaching 50% mortality only after 58, 10, and 5 days at 15°, 25°, and 35 °C, respectively. Larval to pupa molt was only observed in larvae with access to air, whereas individuals kept submerged never molted. Although most of the oxygen was obtained from the air, larvae obtained 12.72% of their oxygen from the water, while pupae took only 5.32%. In both media, temperature affected the respiration rate of the larvae, with relatively close Q₁₀ values (1.56 and 1.83 for water and air, respectively). A similar pattern of O₂ consumption was observed in Ae. albopictus, whose larvae obtained 12.14% of their oxygen from the water. The detailed quantification of oxygen consumption by mosquito larvae showed that water-dissolved oxygen is not negligible and physiologically relevant, challenging the idea that mosquito larvae only breathe atmospheric oxygen.

It is taken for granted that immature mosquito only breathe atmospheric air through their siphons. However, there is no quantitative study that demonstrated it. We analysed the survival of the last instar larvae of Aedes aegypti fully submerged at different temperatures, and measured oxygen consumption from air and dissolved in water, of larvae and pupae of this species under different conditions. Results revealed that under water, larvae survived much longer than expected, reaching 50% mortality only after 58, 10, and 5 days at 15°, 25° and 35°C, respectively. Interestingly, whereas we registered moults to pupae in larvae with access to air, individuals kept submerged never moulted. When remaining at the water surface, larvae obtained 12.72% of O ₂ from the water, while pupae only 5.32%. When completely submerged, larvae consumed less oxygen than in contact with the surface, but enough for surviving, while pupae did not. At both media, temperature affected larvae respiration rate, with relatively close Q ₁₀ values. In the related species, Ae. albopictus , a similar pattern of O ₂ consumption were observed. Larvae got 12.14% of their oxygen from the water. Interestingly, no significant differences in total O ₂ consumption were found between water O ₂ consumption, when Ae. albopictus larvae were submerged, or when they also have access to air (dual O ₂ consumption). Our findings not only challenge the classical idea that mosquito larvae only breathe atmospheric O ₂ , but also force us to reconsider the potential effectiveness of control methods based on asphyxiating larvae by detaching from water surface. Summary statement: We present the first quantitative analysis of mosquito larvae respiration in air and water, unravelling the unknown capacity of larvae of the most cosmopolitan disease vector of breathing underwater.

Species Distribution Modelling (SDM) determines habitat suitability of a species across geographic areas using macro-climatic variables; however, micro-habitats can buffer or exacerbate the influence of macro-climatic variables, requiring links between physiology and species persistence. Experimental approaches linking species physiology to micro-climate are complex, time consuming and expensive. E.g., what combination of exposure time and temperature is important for a species thermal tolerance is difficult to judge a priori . We tackled this problem using an active learning approach that utilized machine learning methods to guide thermal tolerance experimental design for three kissing-bug species (Hemiptera: Reduviidae: Triatominae), vectors of the parasite causing Chagas disease. As with other pathogen vectors, triatomines are well known to utilize micro-habitats and the associated shift in microclimate to enhance survival. Using a limited literature-collected dataset, our approach showed that temperature followed by exposure time were the strongest predictors of mortality; species played a minor role, and life stage was the least important. Further, we identified complex but biologically plausible nonlinear interactions between temperature and exposure time in shaping mortality, together setting the potential thermal limits of triatomines. The results from this data led to the design of new experiments with laboratory results that produced novel insights of the effects of temperature and exposure for the triatomines. These results, in turn, can be used to better model micro-climatic envelope for the species. Here we demonstrate the power of an active learning approach to explore experimental space to design laboratory studies testing species thermal limits. Our analytical pipeline can be easily adapted to other systems and we provide code to allow practitioners to perform similar analyses. Not only does our approach have the potential to save time and money: it can also increase our understanding of the links between species physiology and climate, a topic of increasing ecological importance. Author summary: Species Distribution Modelling determines habitat suitability of a species across geographic areas using macro-climatic variables; however, micro-habitats can buffer or exacerbate the influence of macro-climatic variables, requiring links between physiology and species persistence. We tackled the problem of the combination of exposure time and temperature (a combination difficult to judge a priori ) in determining species thermal tolerance, using an active learning approach that utilized machine learning methods to guide thermal tolerance experimental design for three kissing-bug species, vectors of the parasite causing Chagas disease. These bugs are found in micro-habitats with associated shifts in microclimate to enhance survival. Using a limited literature-collected dataset, we showed that temperature followed by exposure time were the strongest predictors of mortality, that species played a minor role, that life stage was the least important, and a complex nonlinear interaction between temperature and exposure time in shaping mortality of kissing bugs. These results led to the design of new laboratory experiments to assess the effects of temperature and exposure for the triatomines. These results can be used to better model micro-climatic envelope for species. Our active learning approach to explore experimental space to design laboratory studies can also be applied to other environmental conditions or species.

One of the main vectors for malaria in Latin-America is Anopheles pseudopunctipennis (Theobald), whereas Aedes aegypti (L.) is the primary vector of dengue, yellow fever, Zika, and chikungunya viruses. The use of repellents is recommended as personal protection method against these vectors (or mosquitoes), however there are very few studies evaluating the effect of repellents on An. pseudopunctipennis. The use of a Petri dish to study repellence has been applied by several authors on flies, cockroaches, kissing bugs and mosquitoes, being a valuable technique for species that are difficult to breed under laboratory conditions, such as An. pseudopunctipennis, which could be infected by parasites. In the present study we evaluated the repellence of the essential oil of E. nitens, its main component (1,8-cineole) and the commercial repellent DEET on An. pseudopunctipennis and Ae. aegypti females using the plaque repellency method coupled to EthoVision XT10.1 video-tracking software. Repellent effect and locomotor activity were studied through a repellence index (RI) together with an axis constructed from the behavioral variables obtained using the tracking software. DEET repellent effect was observed at 0.01mg/mL for Ae. aegypti and 0.01 and 0.1mg/mL for An. pseudopunctipennis. In addition, the essential oil showed significant repellence at 1 and 10 mg/mL for Ae. aegypti, and 1, 5, 10 and 25 mg/mL for An. pseudopunctipennis, no significant response was detected to 1,8-cineole at any concentration for neither of the two species. This is the first study that evaluates these compounds on An. pseudopunctipennis females and quantify their effects on the activity of both species.