Oviposition behavior of the quasi-gregarious parasitoid, Ooencyrtus kuvanae (Hymenoptera: Encyrtidae).

The parasitoid wasp, Ooencyrtus kuvanae (Howard) (Hymenoptera: Encyrtidae), is a natural enemy of the spongy moth, a significant forest pest in North America. We investigated the oviposition behavior of O. kuvanae females on spongy moth egg masses by (i) presenting female parasitoids with a single spongy moth egg mass that was replaced every day, 2nd day, 4th day, 8th day, or 16th day (which is the total length of the oviposition period) and (ii) presenting female parasitoids with 1, 2, 4, or 8 egg masses at a time. Offspring developmental length ranged from 18 to 24 days. On average, male offspring exhibited faster developmental times, emerging approximately 1 day ahead of females. The amount of time that adult females spent on an egg mass affected the number of parasitized eggs. Specifically, more offspring emerged in the 4-, 8-, and 16-day treatments than in scenarios involving daily or every second-day egg mass replacement. The percentage of male offspring decreased as the number of egg masses presented to females increased. Interestingly, the total number of female offspring remained constant, but the number of male offspring decreased with an increase in the number of egg masses and time spent by the parent within a patch. The observed sexual dimorphism in development time, the influence of resource availability on offspring sex ratios, and flexible oviposition patterns illustrate the adaptability of O. kuvanae in response to varying conditions. These insights have implications for our understanding of parasitoid-host interactions and their potential role in biological control strategies.

The impact of insect egg deposition on Pinus sylvestris transcriptomic and phytohormonal responses to larval herbivory.

Plants can improve their resistance to feeding damage by insects if they have perceived insect egg deposition prior to larval feeding. Molecular analyses of these egg-mediated defence mechanisms have until now focused on angiosperm species. It is unknown how the transcriptome of a gymnosperm species responds to insect eggs and subsequent larval feeding. Scots pine (Pinus sylvestris L.) is known to improve its defences against larvae of the herbivorous sawfly Diprion pini L. if it has previously received sawfly eggs. Here, we analysed the transcriptomic and phytohormonal responses of Scots pine needles to D. pini eggs (E-pine), larval feeding (F-pine) and to both eggs and larval feeding (EF-pine). Pine showed strong transcriptomic responses to sawfly eggs and-as expected-to larval feeding. Many egg-responsive genes were also differentially expressed in response to feeding damage, and these genes play an important role in biological processes related to cell wall modification, cell death and jasmonic acid signalling. EF-pine showed fewer transcriptomic changes than F-pine, whereas EF-treated angiosperm species studied so far showed more transcriptional changes to the initial phase of larval feeding than only feeding-damaged F-angiosperms. However, as with responses of EF-angiosperms, EF-pine showed higher salicylic acid concentrations than F-pine. Based on the considerable overlap of the transcriptomes of E- and F-pine, we suggest that the weaker transcriptomic response of EF-pine than F-pine to larval feeding damage is compensated by the strong, egg-induced response, which might result in maintained pine defences against larval feeding.

Floor eggs in goose breeders: patterns, genetic and environmental influences, and physiological indexes.

A floor egg is an egg that is not laid in the nest, which is a prevalent issue in many fowl breeder farms, lowering egg collection efficiency, hatching performance, and economic benefits. Although the pattern and influencing factors of floor laying have been extensively reported in chickens and ducks, it is not clear in geese. Herein, the Yangzhou goose breeders were selected, and the time and location preferences, genetic and environmental influences, and physiological indexes in floor laying were investigated. The results revealed distinct time and location preferences existed. More floor eggs were laid from 2:00 to 5:00 and 8:00 to 12:00 am, with a concentration observed in the feed trough. Moreover, the proportion of floor eggs was higher at the early stage than at other stages of the laying cycle, and the fast-growing line laid more floor eggs than dual-purpose and high-yielding lines (P < 0.05). In addition to genetic factors, the effect of environmental influences on floor eggs was also surveyed. More floor eggs were observed in the family housing system than in large-group and small-population housing systems, and geese who reared in north-facing houses laid more floor eggs than in south-facing houses (P < 0.05). Physiological indexes were compared between floor-laying and nest-laying geese. Significantly decreased serum progesterone and prolactin levels were detected, alongside down-regulated gene expressions of progesterone receptor in ovaries, oxytocin receptor in both pituitary and ovaries, corticotropin-releasing hormone in ovaries, and dopamine receptor D2 in hypothalamus and ovaries in floor-laying geese compared to nest-laying geese (P < 0.05). In addition, a practical and inexpensive approach of adding a single decoy egg to the nest box effectively reduced the proportion of floor eggs (P < 0.05). Taken together, these data provide scientific information for patterns, genetic and environmental influences, and physiological indexes of floor eggs, thereby contributing to effective control of floor laying in goose breeders' production.

Ovipositional responses of tortricid moths to sugars, salts and neem oil.

Oviposition is essential in the life history of insects and is mainly mediated by chemical and tactile cues present on the plant surface. Oviposition deterrents or stimulants can modify insect oviposition and be employed in pest control. Relatively few gustatory oviposition stimuli have been described for tortricid moths. In this study the effect of NaCl, KCl, sucrose, fructose and neem oil on the number of eggs laid by Cydia pomonella (L.), Grapholita molesta (Busck) and Lobesia botrana (Dennis & Schifermüller) was tested in laboratory arenas containing filter papers loaded with 3 doses of a given stimulus and solvent control. In general, salts increased oviposition at the mid dose (102 M) and sugars reduced it at the highest dose (103 mM), but these effects depended on the species. Neem oil dramatically reduced the number of eggs laid as the dose increased, but the lowest neem oil dose (0.1% v/v) increased L. botrana oviposition relative to solvent control. Our study shows that ubiquitous plant chemicals modify tortricid moth oviposition under laboratory conditions, and that neem oil is a strong oviposition deterrent. The oviposition arena developed in this study is a convenient tool to test the effect of tastants on the oviposition behavior of tortricid moths.

Circadian regulation of calcium and phosphorus homeostasis during the oviposition cycle in laying hens.

Maintenance of calcium and phosphorus homeostasis in laying hens is crucial for preservation of skeletal integrity and eggshell quality, though physiological regulation of these systems is incompletely defined. To investigate changes in mineral and vitamin D3 homeostasis during the 24-h egg formation cycle, 32-wk-old commercial laying hens were sampled at 1, 3, 4, 6, 7, 8, 12, 15, 18, 21, 23, and 24 h post-oviposition (HPOP; n ≥ 4). Ovum location and egg calcification stage were recorded, and blood chemistry, plasma vitamin D3 metabolites, circulating parathyroid hormone (PTH), and expression of genes mediating uptake and utilization of calcium and phosphorus were evaluated. Elevated levels of renal 25-hydroxylase from 12 to 23 HPOP suggest this tissue might play a role in vitamin D3 25-hydroxylation during eggshell calcification. In shell gland, retinoid-x-receptor gamma upregulation between 6 and 8 HPOP followed by subsequently increased vitamin D receptor indicate that vitamin D3 signaling is important for eggshell calcification. Increased expression of PTH, calcitonin, and fibroblast growth factor 23 (FGF23) receptors in the shell gland between 18 and 24 HPOP suggest elevated sensitivity to these hormones toward the end of eggshell calcification. Shell gland sodium-calcium exchanger 1 was upregulated between 4 and 7 HPOP and plasma membrane calcium ATPase 1 increased throughout eggshell calcification, suggesting the primary calcium transporter may differ according to eggshell calcification stage. Expression in shell gland further indicated that bicarbonate synthesis precedes transport, where genes peaked at 6 to 7 and 12 to 18 HPOP, respectively. Inorganic phosphorus transporter 1 (PiT-1) expression peaked in kidney between 12 and 15 HPOP, likely to excrete excess circulating phosphorus, and in shell gland between 18 and 21 HPOP. Upregulation of FGF23 receptors and PiT-1 during late eggshell calcification suggest shell gland phosphorus uptake is important at this time. Together, these findings identified potentially novel hormonal pathways involved in calcium and phosphorus homeostasis along with associated circadian patterns in gene expression that can be used to devise strategies aimed at improving eggshell and skeletal strength in laying hens.

Neuronal substrates of egg-laying behaviour at the abdominal ganglion of Drosophila melanogaster.

Egg-laying in Drosophila is the product of post-mating physiological and behavioural changes that culminate in a stereotyped sequence of actions. Egg-laying harbours a great potential as a paradigm to uncover how the appropriate motor circuits are organized and activated to generate behaviour. To study this programme, we first describe the different phases of the egg-laying programme and the specific actions associated with each phase. Using a combination of neuronal activation and silencing experiments, we identify neurons (OvAbg) in the abdominal ganglion as key players in egg-laying. To generate and functionally characterise subsets of OvAbg, we used an intersectional approach with neurotransmitter specific lines-VGlut, Cha and Gad1. We show that OvAbg/VGlut neurons promote initiation of egg deposition in a mating status dependent way. OvAbg/Cha neurons are required in exploration and egg deposition phases, though activation leads specifically to egg expulsion. Experiments with the OvAbg/Gad1 neurons show they participate in egg deposition. We further show a functional connection of OvAbg neurons with brain neurons. This study provides insight into the organization of neuronal circuits underlying complex motor behaviour.

Conserved temperature requirements but contrasting responses to humidity across oviposition preferences in temperate grasshoppers.

The right choice of an oviposition site is a crucial task for oviparous species without maternal care. In contrast to well investigated biotic factors, e.g., larval food preferences, parasitism, predation, and competition avoiding, abiotic factors affecting oviposition preferences in insects have been rarely investigated in comparative studies. To improve our current understanding of oviposition site selection in Orthoptera, we investigated the influence of substrate temperature and moisture on the oviposition behaviour of 14 temperate grasshopper species. Conspecific groups of adults were kept in arenas with simultaneous temperature and moisture gradients. For each ootheca produced during the experiment (n = 1192) we recorded its depth and local microclimatic conditions. Our results indicate that microclimatic oviposition preferences significantly differ among species, however, correlations between adult habitat preferences and microclimatic oviposition preferences were surprisingly weak. Even oligothermic species preferred substrate temperatures around 30 °C and some xerothermic species preferred higher humidity. The hypothesized tendency to place oothecae closer to the ground within grass tussocks under hot and dry conditions was confirmed. It is possible that species evaluate microclimatic conditions for oviposition in the context of occupied habitat, i.e., in a relative rather than absolute manner.

Egg Morphology of Two Neotropical Dragonflies: Micrathyria hesperis and Miathyria simplex (Odonata: Libellulidae).

Odonata species live through their immature development in aquatic habitats, where the eggs are adapted to survive the initial stages. The survival of the eggs is linked to the layers that make up the eggshell. These layers are common to all odonate species, but show variations among them, depending on the oviposition method. For example, endophytic eggs (laid in plant tissues) and exophytic eggs (laid on the water surface) have different morphologies, which may reveal egg adaptations to environmental conditions and stresses. The differences in the egg morphologies could be shown in the length of the egg layers, their histochemical composition, and in the ultrastructure. The histochemical composition can reveal several features that could lead us to a better understanding of its function, for example, how glycoproteins and total proteins could regulate the humidity and water retention in the eggs according to the environments in which the eggs are placed.

A single neuron in C. elegans orchestrates multiple motor outputs through parallel modes of transmission.

Animals generate a wide range of highly coordinated motor outputs, which allows them to execute purposeful behaviors. Individual neurons in the circuits that generate behaviors have a remarkable capacity for flexibility as they exhibit multiple axonal projections, transmitter systems, and modes of neural activity. How these multi-functional properties of neurons enable the generation of adaptive behaviors remains unknown. Here, we show that the HSN neuron in C. elegans evokes multiple motor programs over different timescales to enable a suite of behavioral changes during egg laying. Using HSN activity perturbations and in vivo calcium imaging, we show that HSN acutely increases egg laying and locomotion while also biasing the animals toward low-speed dwelling behavior over minutes. The acute effects of HSN on egg laying and high-speed locomotion are mediated by separate sets of HSN transmitters and different HSN axonal compartments. The long-lasting effects on dwelling are mediated in part by HSN release of serotonin, which is taken up and re-released by NSM, another serotonergic neuron class that directly evokes dwelling. Our results show how the multi-functional properties of a single neuron allow it to induce a coordinated suite of behaviors and also reveal that neurons can borrow serotonin from one another to control behavior.

Effects of mating on female reproductive physiology in the insect model, Rhodnius prolixus, a vector of the causative parasite of Chagas disease.

The blood-sucking hemipteran Rhodnius prolixus is one of the main vectors of Chagas disease, a neglected tropical disease that affects several million people worldwide. Consuming a blood meal and mating are events with a high epidemiological impact since after each meal, mated females can lay fertile eggs that result in hundreds of offspring. Thus, a better knowledge of the control of R. prolixus reproductive capacity may provide targets for developing novel strategies to control vector populations, thereby reducing vector-host contacts and disease transmission. Here, we have used a combination of gene transcript expression analysis, biochemical assays, hormone measurements and studies of locomotory activity to investigate how mating influences egg development and egg laying rates in R. prolixus females. The results demonstrate that a blood meal increases egg production capacity and leads to earlier egg laying in mated females compared to virgins. Virgin females, however, have increased survival rate over mated females. Circulating juvenile hormone (JH) and ecdysteroid titers are increased in mated females, a process mainly driven through an upregulation of the transcripts for their biosynthetic enzymes in the corpus allatum and ovaries, respectively. Mated females display weaker locomotory activity compared to virgin females, mainly during the photophase. In essence, this study shows how reproductive output and behaviour are profoundly influenced by mating, highlighting molecular, biochemical, endocrine and behavioral features differentially expressed in mated and virgin R. prolixus females.

Odour-mediated oviposition site selection in Aedes aegypti depends on aquatic stage and density.

BACKGROUND: Olfaction plays an important role in the selection and assessment of oviposition sites by mosquitoes. Volatile organic compounds (VOCs) associated with potential breeding sites affect the behaviour of gravid mosquitoes, with VOCs from aquatic stages of conspecific mosquitoes influencing and regulating oviposition. The purpose of this study was to conduct a systematic analysis of the behavioural response of gravid Aedes aegypti to conspecific aquatic stage-conditioned water, to identify the associated bioactive VOCs and to determine how blends of these VOCs regulate oviposition site selection and stimulate egg-laying. METHODS: Using a multi-choice olfactory oviposition assay, controlling for other sensory modalities, the responses of individual females to water conditioned with different densities of conspecific aquatic stages were assessed. The conditioned water samples from the most preferred density of each aquatic stage were subsequently compared to each other using the same oviposition assay and analysed using an analysis of variance (ANOVA) followed by a Tukey post-hoc test. Using combined gas chromatography and electroantennographic detection or mass spectrometry, bioactive VOCs from the preferred density of each aquatic stage were identified. Synthetic blends were prepared based on the identified ratios of bioactive VOCs in the aquatic stages, and then tested to determine the oviposition choice of Ae. aegypti in a dose-dependent manner, against a solvent control, using a dual-choice assay. This dataset was analysed using nominal logistic regression followed by an odds ratio comparison. RESULTS: Gravid Ae. aegypti responded stage- and density-dependently to water conditioned with eggs, second- and fourth-instar larvae, and pupal exuviae, but not to water conditioned with pupae alone. Multi-choice assays demonstrated that gravid mosquitoes preferred to oviposit in water conditioned with fourth-instar larvae, over the other aquatic stage-conditioned water. Gravid Ae. aegypti were attracted, and generally stimulated, to oviposit in a dose-dependent manner to the individual identified synthetic odour blends for the different aquatic stages. CONCLUSIONS: Intraspecific VOCs regulate oviposition site selection in Ae. aegypti in a stage- and density-dependent manner. We discuss the need for further studies to evaluate the identified synthetic blends to modulate the odour-mediated oviposition of Ae. aegypti under field conditions.

Haematological parameters of laying hens under different group size.

The relevance of this study lies in its potential implications for poultry farming practices and animal welfare. Understanding the impact of group size on the blood parameters of hens can provide valuable insights for optimising their health and well-being in farming environments. The aim of the study was an analysis of haematological parameters of laying hens under the influence group size with the same stoking density in analogous cages by design. Hens were kept for 34 weeks in cages of multilevel batteries at different group sizes: I group-93 birds, II group-52 birds, III group-17 birds and IV group-9 birds. The study analysed blood samples from laying hens at 18 and 52 weeks of age. Results showed that reducing the group size from 93 to 52 birds led to a haematological status within the physiological norm, characterized by increased heterophils and decreased monocyte levels. Whereas, the decrease in group size to 17 birds was accompanied by a decrease in the hens' blood content of thrombocytes, an increase of heterophile, a decrease of monocytes and lymphocytes within the physiological norm, as well as an increase in the heterophiles to lymphocytes ratio.

A rise-to-threshold process for a relative-value decision.

Whereas progress has been made in the identification of neural signals related to rapid, cued decisions1-3, less is known about how brains guide and terminate more ethologically relevant decisions in which an animal's own behaviour governs the options experienced over minutes4-6. Drosophila search for many seconds to minutes for egg-laying sites with high relative value7,8 and have neurons, called oviDNs, whose activity fulfills necessity and sufficiency criteria for initiating the egg-deposition motor programme9. Here we show that oviDNs express a calcium signal that (1) dips when an egg is internally prepared (ovulated), (2) drifts up and down over seconds to minutes-in a manner influenced by the relative value of substrates-as a fly determines whether to lay an egg and (3) reaches a consistent peak level just before the abdomen bend for egg deposition. This signal is apparent in the cell bodies of oviDNs in the brain and it probably reflects a behaviourally relevant rise-to-threshold process in the ventral nerve cord, where the synaptic terminals of oviDNs are located and where their output can influence behaviour. We provide perturbational evidence that the egg-deposition motor programme is initiated once this process hits a threshold and that subthreshold variation in this process regulates the time spent considering options and, ultimately, the choice taken. Finally, we identify a small recurrent circuit that feeds into oviDNs and show that activity in each of its constituent cell types is required for laying an egg. These results argue that a rise-to-threshold process regulates a relative-value, self-paced decision and provide initial insight into the underlying circuit mechanism for building this process.

Social modulation of oogenesis and egg laying in Drosophila melanogaster.

Being part of a group facilitates cooperation between group members but also creates competition for resources. This is a conundrum for gravid females, whose future offspring benefit from being in a group only if there are enough resources relative to group size. Females may therefore be expected to modulate reproductive output depending on social context. In the fruit fly Drosophila melanogaster, females actively attract conspecifics to lay eggs on the same resources, generating groups in which individuals may cooperate or compete. The genetic tractability of this species allows dissecting the mechanisms underlying physiological adaptation to social context. Here, we show that females produce eggs increasingly faster as group size increases. By laying eggs faster when grouped than when isolated, females reduce competition between offspring and increase offspring survival. In addition, grouped females lay eggs during the day, while isolated females lay them at night. We show that responses to the presence of others requires visual input and that flies from any sex, mating status, or species can trigger these responses. The mechanisms of this modulation of egg laying by group is connected to a lifting of the inhibition of light on oogenesis and egg laying, possibly mediated in part by an increase in juvenile hormone activity. Because modulation of reproduction by social context is a hallmark of animals with higher levels of sociality, our findings in a species considered solitary question the validity of this nomenclature and suggest a widespread and profound influence of social context on reproduction.

Cross-generation pheromonal communication drives Drosophila oviposition site choice.

In a heterogeneous and changing environment, oviposition site selection strongly affects the survival and fitness of the offspring.1,2 Similarly, competition between larvae affects their prospects.3 However, little is known about the involvement of pheromones in regulating these processes.4,5,6,7,8 Here, we show that mated females of Drosophila melanogaster prefer to lay eggs on substrates containing extracts of conspecific larvae. After analyzing these extracts chemically, we test each compound in an oviposition assay and find that mated females display a dose-dependent preference to lay eggs on substrates spiked with (Z)-9-octadecenoic acid ethyl ester (OE). This egg-laying preference relies on gustatory receptor Gr32a and tarsal sensory neurons expressing this receptor. The concentration of OE also regulates larval place choice in a dose-dependent manner. Physiologically, OE activates female tarsal Gr32a+ neurons. In conclusion, our results reveal a cross-generation communication strategy essential for oviposition site selection and regulation of larval density.

Identification of volatile compounds from fruits aroma and citrus essential oils and their effect on oviposition of Ceratitis capitata (Diptera: Tephritidae).

Ceratitis capitata (Wiedemann), also known as the Mediterranean fruit fly, is one of the most serious pests for several fresh fruit commodities causing extensive fruit losses worldwide. The response of C. capitata adults to fruit and nonfruit volatiles has been extensively studied. However, the linkage between fruit volatiles and the female ovipositional choice has not been fully elucidated. The present study focused on identifying the volatile organic compounds emitted by detached intact fresh fruits (oranges, lemons, bergamots, and apples) and citrus essential oils and evaluate their effect on Mediterranean fruit fly oviposition. There were more than 130 and 45 volatiles compounds detected in fruits odors and citrus essential oils, respectively. The volatile profile of fruits was dominated either from terpenes and terpenoids or from esters of butanoic, hexanoic, and octanoic acids while limonene was by far the most abundant compound in all citrus essential oils. Oviposition of C. capitata was strongly affected by volatiles emanated from both intact fruit and the citrus essential oils. Regarding the volatiles of the intact fruits, the odor of sweet orange elicited strong oviposition responses to females, while bergamot had the least stimulatory effect on oviposition. Bergamot oil also elicited the least oviposition stimulation compared to sweet orange and lemon essential oils. Our discussion elaborates on the role of fruit volatiles on host finding behavior and fruit susceptibility to C. capitata infestation and includes possible practical implication of the above findings.

Predation stress experienced as immature mites extends their lifespan.

The early-life experience is important in modulating the late-life performance of individuals. It has been predicted that there were trade-offs between early-life fitness and late-life success. Most of the studies on senescence have focused on the trade-offs between the reproduction and lifespan, and the influences of diet, mating, and other factors. Because the negative, non-consumptive effects of predators could also modulate the behaviour and underlying mechanisms of the prey, this study aimed to examine the different effects of predator-induced stress experienced in the early life compared with later life of the prey. The prey (Tyrophagus putrescentiae) was exposed to predation stress from the predator (Neoseiulus cucumeris) during different periods of its life (immature, oviposition period, and post-oviposition period). The results showed that the predation stress experienced during immature stages delayed development by 7.3% and prolonged lifespan by 9.7%, while predation stress experienced in the adult stage (both oviposition and post-oviposition periods) decreased lifespans of T. putrescentiae (by 24.8% and 28.7%, respectively). Predation stress experienced during immature stages also reduced female fecundity by 7.3%, whereas that experienced during the oviposition period reduced fecundity of the prey by 50.7%. This study demonstrated for the first time lifespan extension by exposure to predation stress when young and highlighted the importance of early-life experience to aging and lifespan.

Adaptive Plasticity of Insect Eggs in Response to Environmental Challenges.

Insect eggs are exposed to a plethora of abiotic and biotic threats. Their survival depends on both an innate developmental program and genetically determined protective traits provided by the parents. In addition, there is increasing evidence that (a) parents adjust the egg phenotype to the actual needs, (b) eggs themselves respond to environmental challenges, and (c) egg-associated microbes actively shape the egg phenotype. This review focuses on the phenotypic plasticity of insect eggs and their capability to adjust themselves to their environment. We outline the ways in which the interaction between egg and environment is two-way, with the environment shaping the egg phenotype but also with insect eggs affecting their environment. Specifically, insect eggs affect plant defenses, host biology (in the case of parasitoid eggs), and insect oviposition behavior. We aim to emphasize that the insect egg, although it is a sessile life stage, actively responds to and interacts with its environment.

Peptidergic modulation of a multi-functional central pattern generator in the pulmonate snail.

Egg laying in pulmonate snails is a well-orchestrated process that involves a period of reduced locomotion, followed by substrate cleaning with rhythmic rasping of the surface to make tiny grooves, into which eggs are deposited. Although the neurohormonal control of initiating egg laying has been well established, the signals that modulate the buccal central pattern generator to substrate cleaning during egg laying are not known. Neuropeptides of the invertebrate gonadotropin-releasing hormone/corazonin family (invGnRH/CRZ) have been shown to be involved in reproduction and allied behaviors in many vertebrates and invertebrates. Here, we show that the buccal motor pattern underlying substrate cleaning during egg laying is altered by a vertebrate GnRH agonist. Signals from the intestinal nerve innervating reproductive structures, previously shown to be both necessary and sufficient for egg-laying behaviors, are blocked by a vertebrate GnRH antagonist. Further, the vertebrate GnRH-triggered response elicits rhythmic, phase 2 and non-phase 2 activity in the buccal motor pattern, with a shutdown of phase 3, indicative of repetitive rasping without accompanied swallowing behavior. Using immunohistochemistry, intracellular electrophysiology and extracellular nerve stimulation, we show that a member of the invGnRH/CRZ family of neuropeptides could be the signal that contextually switches the multifunctional buccal CPG to a biphasic rasping rhythm that underlies substrate cleaning behavior during egg laying in the pulmonate snail Planorbella (Helisoma) trivolvis.

Single amino acid residue mediates reciprocal specificity in two mosquito odorant receptors.

The southern house mosquito, Culex quinquefasciatus, utilizes two odorant receptors, CquiOR10 and CquiOR2, narrowly tuned to oviposition attractants and well conserved among mosquito species. They detect skatole and indole, respectively, with reciprocal specificity. We swapped the transmembrane (TM) domains of CquiOR10 and CquiOR2 and identified TM2 as a specificity determinant. With additional mutations, we showed that CquiOR10A73L behaved like CquiOR2. Conversely, CquiOR2L74A recapitulated CquiOR10 specificity. Next, we generated structural models of CquiOR10 and CquiOR10A73L using RoseTTAFold and AlphaFold and docked skatole and indole using RosettaLigand. These modeling studies suggested space-filling constraints around A73. Consistent with this hypothesis, CquiOR10 mutants with a bulkier residue (Ile, Val) were insensitive to skatole and indole, whereas CquiOR10A73G retained the specificity to skatole and showed a more robust response than the wildtype receptor CquiOR10. On the other hand, Leu to Gly mutation of the indole receptor CquiOR2 reverted the specificity to skatole. Lastly, CquiOR10A73L, CquiOR2, and CquiOR2L74I were insensitive to 3-ethylindole, whereas CquiOR2L74A and CquiOR2L74G gained activity. Additionally, CquiOR10A73G gave more robust responses to 3-ethylindole than CquiOR10. Thus, we suggest the specificity of these receptors is mediated by a single amino acid substitution, leading to finely tuned volumetric space to accommodate specific oviposition attractants.