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Aedes aegypti mosquitoes are major vectors of dengue, chikungunya, and other arboviral diseases. Ae. aegypti 's capacity to reproduce and to spread disease depends on the female mosquitoes' ability to obtain blood meals and find water-filled containers in which to lay eggs (oviposit). While humidity sensation (hygrosensation) has been implicated in these behaviors, the specific hygrosensory pathways involved have been unclear. Here, we establish the distinct molecular requirements and anatomical locations of Ae. aegypti Dry Cells and Moist Cells and examine their contributions to behavior. We show that Dry Cell and Moist Cell responses to humidity involve different ionotropic receptor (IR) family sensory receptors, with dry air-activated Dry Cells reliant upon the IR Ir40a , and humid air-activated Moist Cells upon Ir68a . Both classes of hygrosensors innervate multiple antennal sensilla, including sensilla ampullacea near the antennal base as well as two classes of coeloconic sensilla near the tip. Dry Cells and Moist Cells each support behaviors linked to mosquito reproduction but contribute differently: Ir40a -dependent Dry Cells act in parallel with Ir68a -dependent Moist Cells to promote blood feeding, while oviposition site seeking is driven specifically by Ir68a- dependent Moist Cells. Together these findings reveal the importance of distinct hygrosensory pathways in blood feeding and oviposition site seeking and suggest Ir40a- dependent Dry Cells and Ir68a- dependent Moist Cells as potential targets for vector control strategies., Competing Interests: Competing interests statement:P.A.G. is an inventor on patent WO2017196861A1 (WIPO PCT; pending; inventors: Z. Knecht, P. Garrity, L. Ni). “Methods for modulating insect hygro and/or thermosensation.” This patent proposes using ionotropic receptors as targets to disrupt hygrosensation and thermosensation in insects.

Gustatory receptors (GRs) are critical for insect chemosensation and are potential targets for controlling pests and disease vectors, making their structural investigation a vital step toward such applications. We present structures of Bombyx mori Gr9 (BmGr9), a fructose-gated cation channel, in agonist-free and fructose-bound states. BmGr9 forms a tetramer similar to distantly related insect odorant receptors (ORs). Upon fructose binding, BmGr9's channel gate opens through helix S7b movements. In contrast to ORs, BmGr9's ligand-binding pocket, shaped by a kinked helix S4 and a shorter extracellular S3-S4 loop, is larger and solvent accessible in both agonist-free and fructose-bound states. Also, unlike ORs, fructose binding by BmGr9 involves helix S5 and a pocket lined with aromatic and polar residues. Structure-based sequence alignments reveal distinct patterns of ligand-binding pocket residue conservation in GR subfamilies associated with different ligand classes. These data provide insight into the molecular basis of GR ligand specificity and function., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Animals commonly use thermosensation, the detection of temperature and its variation, for defensive purposes: to maintain appropriate body temperature and to avoid tissue damage. However, some animals also use thermosensation to go on the offensive: to hunt for food. The emergence of heat-dependent foraging behavior has been accompanied by the evolution of diverse thermosensory organs of often exquisite thermosensitivity. These organs detect the heat energy emitted from food sources that range from nearby humans to trees burning in a forest kilometers away. Here, we examine the biophysical considerations, anatomical specializations and molecular mechanisms that underlie heat-driven foraging. We focus on three groups of animals that each meet the challenge of detecting heat from potential food sources in different ways: (1) disease-spreading vector mosquitoes, which seek blood meals from warm-bodied hosts at close range, using warming-inhibited thermosensory neurons responsive to conductive and convective heat flow; (2) snakes (vipers, pythons and boas), which seek warm-blooded prey from ten or more centimeters away, using warmth-activated thermosensory neurons housed in an organ specialized to harvest infrared radiation; and (3) fire beetles, which maximize their offspring's feeding opportunities by seeking forest fires from kilometers away, using mechanosensory neurons housed in an organ specialized to convert infrared radiation into mechanosensory stimuli. These examples highlight the diverse ways in which animals exploit the heat emanating from potential food sources, whether this heat reflects ongoing metabolic activity or a recent lightning strike, to secure a nutritious meal for themselves or for their offspring., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2023. Published by The Company of Biologists Ltd.)

The advent of CRISPR/Cas9-mediated genome editing has expanded the range of animals amenable to targeted genetic analysis. This has accelerated research in animals not traditionally studied using molecular genetics. However, studying genes essential for reproduction or survival in such animals remains challenging, as they lack the tools that aid genetic analysis in traditional genetic model organisms. We recently introduced the use of distinguishably marked knock-in pairs (DMKPs) as a strategy for rapid and reliable genotyping in such species. Here we show that DMKPs also facilitate the maintenance and study of mutations that cannot be maintained in a homozygous state, a group which includes recessive lethal and sterile mutations. Using DMKPs, we disrupt the zero population growth locus in Drosophila melanogaster and in the dengue vector mosquito Aedes aegypti. In both species, DMKPs enable the maintenance of zero population growth mutant strains and the reliable recovery of zero population growth mutant animals. Male and female gonad development is disrupted in fly and mosquito zero population growth mutants, rendering both sexes sterile. In Ae. aegypti, zero population growth mutant males remain capable of inducing a mating refractory period in wild-type females and of competing with wild-type males for mates, properties compatible with zero population growth serving as a target in mosquito population suppression strategies. DMKP is readily generalizable to other species amenable to CRISPR/Cas9-mediated gene targeting, and should facilitate the study of sterile and lethal mutations in multiple organisms not traditionally studied using molecular genetics., Competing Interests: Conflicts of interest W.J.L. and P.A.G. are co-inventors on patent application PCT/US2021/052374, “Sterile organisms, methods of making, and methods of use thereof”. This patent includes methods for genetic manipulations in non-traditional model organisms ., (© The Author(s) 2023. Published by Oxford University Press on behalf of The Genetics Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

To reproduce and to transmit disease, female mosquitoes must obtain blood meals and locate appropriate sites for egg laying (oviposition). While distinct sensory cues drive each behavior, humidity contributes to both. Here, we identify the mosquito's humidity sensors (hygrosensors). Using generalizable approaches designed to simplify genetic analysis in non-traditional model organisms, we demonstrate that the ionotropic receptor Ir93a mediates mosquito hygrosensation as well as thermosensation. We further show that Ir93a-dependent sensors drive human host proximity detection and blood-feeding behavior, consistent with the overlapping short-range heat and humidity gradients these targets generate. After blood feeding, gravid females require Ir93a to seek high humidity associated with preferred egg-laying sites. Reliance on Ir93a-dependent sensors to promote blood feeding and locate potential oviposition sites is shared between the malaria vector Anopheles gambiae and arbovirus vector Aedes aegypti. These Ir93a-dependent systems represent potential targets for efforts to control these human disease vectors., Competing Interests: Declaration of interests P.A.G. is a co-inventor on patent WO2017196861A1 (WIPO PCT; pending; inventors: Z. Knecht, P. Garrity, L. Ni) “Methods for modulating insect hygro- and/or thermosensation.” This patent proposes using members of the ionotropic receptor family as targets for strategies to disrupt hygro- and thermo-sensation in insects. W.J.L. and P.A.G. are co-inventors on patent application PCT/US2021/052374, “Sterile organisms, methods of making, and methods of use thereof.” This patent includes methods for genetic manipulations in non-traditional model organisms., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Regulation of salt intake is important for animals from flies to humans. A new study clarifies the molecular receptors mediating attraction to low salt concentrations in Drosophila, suggesting a surprisingly fly-specific solution to the challenge of detecting this universal tastant., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2022 Elsevier Inc. All rights reserved.)