A direct test of the effects of changing atmospheric pressure on the mating behavior of Drosophila melanogaster

Sexual conflict and sexual networks in bed bugs: the fitness cost of traumatic insemination, female avoidance and male mate choice

Sexual conflict is prevalent among animals and is primarily caused by the fact that the optimal mating rates are often higher in males than in females. While there is a growing appreciation that females can also gain from multiple matings, we still know relatively little about which sex controls the observed mating rates and how close it is to the optimal female mating rates. To address this issue, we tracked female bed bugs (Cimex lectularius) inseminated daily versus weekly and found that weekly inseminated females lived longer and produced over 50% more offspring. In a follow-up experiment employing a social network framework, we placed 24 bed bugs into a semi-naturalistic arena and recorded all sexual interactions. While recently inseminated females did not avoid males more often, they were more frequently rejected by males. Finally, we tracked avoidance behaviour in a single cohort of female bed bugs as they received six successive daily inseminations. Avoidance rates increased and insemination durations decreased with increasing number of prior inseminations. Overall, our results indicate high costs of polyandry. Although females possess some plastic avoidance strategies, the observed rates of insemination fall closer to the male rather than female optimum.

Quantifying Aedes aegypti Host Odor Preference Using a Two-Port Olfactometer

Blood-feeding mosquitoes are a leading threat to global public health-vectoring dangerous infections including Zika, dengue, and malaria. Mosquitoes identify and target hosts for blood meals by using visual, thermal, and chemical cues. Here we describe an assay for measuring odor-based host-preference behavior-that is, the preferential approach toward one host over another based on differences in the volatile compounds they emit. The assay can be adapted for use with diverse odor sources, from live animals and their breath to odor-scented sleeves with controlled amounts of CO₂ Mosquitoes in this assay fly upwind to within 30 cm of the odor source and then enter a small trap. We therefore believe this assay best replicates medium- to short-range host-seeking, when females approach and are preparing to land on a host animal. We also find that relative response in a two-choice test shows less trial-to-trial variation than the absolute number of responsive mosquitoes, which appears more sensitive to exogenous factors such as rearing conditions. This assay has been used to better understand mosquito host-seeking decisions, which can provide fundamental insight into the brain and behavior as well as information useful for the design of novel vector control strategies.

Quick shift in volatile attraction between the third and fifth instar larvae of Endoclita signifier

BACKGROUND

Endoclita signifer is a polyphagous lepidopteran species of eucalyptus that selects its hosts in the third-instar larval period. To understand how it adapts to its host during development, we studied the olfactory responses of late-stage (fifth)-instar larvae to the dynamic chemical environment they encounter.

RESULTS

Thirty-two volatiles from eucalyptus trunk and soil were identified, among which 14 showed electroantennal activity and five were identified as new. Further behavioral bioassay showed that both β-pinene and the imitation ratio of six key volatile in eucalyptus trunk were attractive to the fifth-instar larvae, but both eliminated and increased β-pinene in the mixture decreased the choice ratio and showed no attraction. Although E. signifer larvae shifted their attraction from o-cymene at the third-instar stage to β-pinene at the fifth-instar stage in a single volatile, the appropriate ratio of the main compounds in eucalyptus trunk volatile is the key to the behavior choice of fifth-instar larvae.

CONCLUSION

The switch in olfactory attraction to different compounds between fifth- and third-instar larvae indicated an olfactory plasticity between third- and fifth-instar larvae. And the particular blend mediated the highly specialized communication interactions specificity between fifth-instar larvae and eucalyptus trunk volatile indicated the specialized host adaptation to fifth-instar larvae. This enhances understanding of how the primitive lepidopteran E. signifier, as a native pest, adapts to introduced eucalyptus. Moreover, this study provides knowledge for the screening and development of target volatiles for trapping and managing E. signifer larvae. © 2022 Society of Chemical Industry.

Weather Sensitivity of Sugar Bait Trapping of Nocturnal Moths: A Case Study from Northern Europe

Assemblages of insects need to be quantitatively sampled in the context of various research questions. Light trapping is the most widely used method for sampling nocturnal Lepidoptera. Attracting moths to sugar baits offers a viable alternative. However, this method is rarely used in professional research despite its popularity among amateur lepidopterists. As the activity of insects is strongly dependent on ambient conditions, the sensitivity of any trapping method to weather parameters needs to be known for the quantitative interpretation of trapping results. In the present paper, we report data on the weather dependence of moth catches obtained by automatic bait traps. The study was performed in Estonia, representing the European hemiboreal forest zone. Portable weather stations set up next to each of the traps were used for collecting weather data. Both abundance and diversity of the moths in the catches depended strongly positively on temperature and negatively on air humidity. Diversity was also negatively correlated with air pressure and positively with the change in pressure during the night. The results show that in situ recording of weather parameters in connection to insect trapping provides useful insights for the study of insect behaviour and the interpretation of the results of monitoring projects.

Automated Barometric Chamber for Entomology Experiments: Arthropods’ Behavior and Insect-Plant Interactions

Insect behaviors, such as flying, oviposition, parasitism, mating/calling, response to semiochemicals, and others, might be influenced by barometric pressure fluctuations. Abiotic factors controlled in the laboratory facilitate the observation of particularities related to development, behavior, and/or habits of arthropods and plants and their interactions. This study aimed to design an automated barometric chamber for research on arthropod behaviors and insect–plant interactions in the laboratory. The barometric chamber is a transparent box equipped with a single-board computer. An air pump and two proportional solenoid valves were used as actuators to control the air flow, while barometric pressure, air humidity, and temperature sensors were used to monitor the conditions within the chamber. A graphical user interface to operate the barometric chamber was developed to run in a web browser. The barometric chamber was designed to allow the barometric pressure to be changed by up to 15 hPa with respect to the local barometric pressure. In addition, the control system makes it possible to set the rise/fall time (ramp) corresponding to the duration in which a change of pressure will be conditioned. Short- and long-term evaluations demonstrated that the control system can assure pressure stability of ±0.1 hPa with respect to the setpoint value. For demonstration purposes, two experiments were carried out to evaluate the influence of barometric pressure on the feeding activity of Euschistus heros and Diabrotica speciosa. For E. heros, the number of stylet sheath was significantly increased under high pressure conditions compared to the low pressure. However, for D. speciosa, there was no statistical difference in leaf consumption at the evaluated testing conditions.

Intraspecific Genetic Variation for Behavioral Isolation Loci in Drosophila

Behavioral isolation is considered to be the primary mode of species isolation, and the lack of identification of individual genes for behavioral isolation has hindered our ability to address fundamental questions about the process of speciation. One of the major questions that remains about behavioral isolation is whether the genetic basis of isolation between species also varies within a species. Indeed, the extent to which genes for isolation may vary across a population is rarely explored. Here, we bypass the problem of individual gene identification by addressing this question using a quantitative genetic comparison. Using strains from eight different populations of Drosophila simulans, we genetically mapped the genomic regions contributing to behavioral isolation from their closely related sibling species, Drosophila mauritiana. We found extensive variation in the size of contribution of different genomic regions to behavioral isolation among the different strains, in the location of regions contributing to isolation, and in the ability to redetect loci when retesting the same strain.

A Link between Atmospheric Pressure and Fertility of Drosophila Laboratory Strains

Simple Summary

The researchers usually keep insects under study under thoroughly controlled conditions. However, sometimes they encounter a situation where the data they obtained under such conditions demonstrate an obvious side effect of some unaccounted factor. Here we provide evidence that changes in atmospheric pressure could be responsible for some such cases.

Abstract

Standardization of conditions under which insects are kept is of great importance when studying their physiology and researchers do their best to maintain it. Nevertheless, sometimes an obvious side effect of some unaccounted factor affecting insects’ reproduction can be revealed even under thoroughly controlled laboratory conditions. We faced such a phenomenon when studying the fertility level in two wild type Drosophila melanogaster strains. For fertility analysis, 50 newly emerged females and 50 males of each strain under study were transferred to fresh medium daily within 10 days. We found out that fertility of both strains was stable on days 2–10 after the oviposition onset in one experiment, while in another one it was significantly decreased during days 5–10. When compared to publicly available meteorological data, these changes in the fertility level demonstrated a strong association with one weather factor: barometric pressure. Thus, we conclude that changes in atmospheric pressure can be considered a factor affecting insects reproduction and discuss a possible mechanism of their influence on fertility.

No water, no mating: Connecting dots from behaviour to pathways

Insects hold considerable ecological and agricultural importance making it vital to understand the factors impacting their reproductive output. Environmental stressors are examples of such factors which have a substantial and significant influence on insect reproductive fitness. Insects are also ectothermic and small in size which makes them even more susceptible to environmental stresses. The present study assesses the consequence of desiccation on the mating latency and copulations duration in tropical Drosophila melanogaster. We tested flies for these reproductive behavioral parameters at varying body water levels and with whole metabolome analysis in order to gain a further understanding of the physiological response to desiccation. Our results showed that the duration of desiccation is positively correlated with mating latency and mating failure, while having no influence on the copulation duration. The metabolomic analysis revealed three biological pathways highly affected by desiccation: starch and sucrose metabolism, galactose metabolism, and phenylalanine, tyrosine and tryptophan biosynthesis. These results are consistent with carbohydrate metabolism providing an energy source in desiccated flies and also suggests that the phenylalanine biosynthesis pathway plays a role in the reproductive fitness of the flies. Desiccation is a common issue with smaller insects, like Drosophila and other tropical insects, and our findings indicate that this lack of ambient water can immediately and drastically affect the insect reproductive behaviour, which becomes more crucial because of unpredictable and dynamic weather conditions.

Low Barometric Pressure Enhances Tethered-Flight Performance and Reproductive of the Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae)

Barometric pressure is an important factor influencing several insect traits. Most studies have been conducted on the behavior of insects in relation to rapid and slight changes in pressure magnitudes or short-term pressure trends, but there is little information on the effect of long-term and large pressure variations on insect traits. Here, we assessed the effects of static low barometric pressure on the tethered flight, lifespan and reproductive performance of Mythimna separata (Walker), a long-distance migratory insect, using an apparatus simulating low barometric pressure at altitudes of 500 m above sea level. We found that both the flight distance and flight duration of M. separata moths were significantly longer under low barometric pressure conditions. Exposure to low barometric pressure conditions for 24 and 48 h significantly shortened the lifespan of female moths but had no influence on male moths. The ovaries of female moths developed earlier, and the preoviposition and oviposition periods were significantly shortened under low atmospheric pressure. Moreover, low atmospheric pressure reduced the respiration rate of female moths. However, there was an increase in the respiration rate of female moths after being returned to standard barometric pressure conditions. Our results show that the behavior and physiological traits of insects are affected by the low-pressure environment during migration. The low barometric pressure conditions at high altitudes is one of important factors accelerating reproductive behavior of M. separata after migration.

Genes underlying species differences in cuticular hydrocarbon production between Drosophila melanogaster and D. simulans

Surface chemical compounds are key components of survival and reproduction in many species. Cuticular hydrocarbons (CHCs) are chemical compounds produced by all insects that are used for both desiccation resistance and chemical communication, including communication related to mating. In the species pair of Drosophila melanogaster and D. simulans, female CHCs stimulate conspecific males to mate and repel heterospecific males. While CHCs are a critical contributor to both reproductive success within a species and isolation between species, few genes underlying species variation in CHC profiles are known. Here, we use genetic mapping of the 3rd chromosome to test a suite of candidate genes for interspecies variation in CHCs. Candidate gene CG5946 was found to be involved in species differences in the production of 7,11-heptacosadiene and 7-tricosene between D. melanogaster and D. simulans. This is therefore a new candidate locus contributing to species-specific variation in the CHC profile. In the process of mapping genes for CHCs, we also identified 29 candidate genes for the reduced survival or inviability of interspecies hybrids.

Environmental cue affects the hearing-related behaviors of Drosophila melanogaster by targeting the redox pathways

Environmental cues like noise, pressure, and circadian rhythm can affect the hearing ability of human beings. Nevertheless, the complex physiology of the human being does not allow us to understand how these factors can affect hearing and hearing-related behaviors. Conversely, these effects can be easily checked using the hearing organ of Drosophila melanogaster, the Johnston organ. In the current study, the Drosophila was exposed to challenging environments like noise, low pressure, and altered circadian rhythm. The hearing organ of larvae, as well as adults, was analyzed for hearing-related defects. In the third instar larva, the cell deaths were detected in the antenna imaginal disc, the precursor of Johnston's organ. Elevated levels of reactive oxygen species and antioxidant enzymes were also detected in the adult antennae of environmentally challenged flies. The ultrastructure of the antennae suggests the presence of abundant mitochondria in the scolopidia of control. Fewer amounts of mitochondria are found in the environmentally challenged adult antennae. In adults, various hearing-related behaviors were analyzed as a readout of functionality of the hearing organ. Analysis of climbing, aggressive, and courtship behaviors suggests abnormal behavior in environmentally challenged flies than the control. The current study suggests that the environmental cues can alter hearing-related behaviors in Drosophila. The methods used in this study can be used to monitor the environmental pollution or to study the effect of alteration of noise, pressure, and circadian rhythm on hearing-related behaviors taking Drosophila melanogaster as a model organism. Graphical abstract.

The fruitless gene affects female receptivity and species isolation

Female mate rejection acts as a major selective force within species, and can serve as a reproductive barrier between species. In spite of its critical role in fitness and reproduction, surprisingly little is known about the genetic or neural basis of variation in female mate choice. Here, we identify fruitless as a gene affecting female receptivity within Drosophila melanogaster, as well as female Drosophila simulans rejection of male D. melanogaster. Of the multiple transcripts this gene produces, by far the most widely studied is the sex-specifically spliced transcript involved in the sex determination pathway. However, we find that female rejection behaviour is affected by a non-sex-specifically spliced fruitless transcript. This is the first implication of fruitless in female behaviour, and the first behavioural role identified for a fruitless non-sex-specifically spliced transcript. We found that this locus does not influence preferences via a single sensory modality, examining courtship song, antennal pheromone perception, or perception of substrate vibrations, and we conclude that fruitless influences mate choice via the integration of multiple signals or through another sensory modality.

Social behavior and aging: A fly model

The field of behavioral genetics has recently begun to explore the effect of age on social behaviors. Such studies are particularly important, as certain neuropsychiatric disorders with abnormal social interactions, like autism and schizophrenia, have been linked to older parents. Appropriate social interaction can also have a positive impact on longevity, and is associated with successful aging in humans. Currently, there are few genetic models for understanding the effect of aging on social behavior and its potential transgenerational inheritance. The fly is emerging as a powerful model for identifying the basic molecular mechanisms underlying neurological and neuropsychiatric disorders. In this review, we discuss these recent advancements, with a focus on how studies in Drosophila melanogaster have provided insight into the effect of aging on aspects of social behavior, including across generations.

Empirical Dynamic Modelling Identifies different Responses of Aedes Polynesiensis Subpopulations to Natural Environmental Variables

To control mosquito populations for managing vector-borne diseases, a critical need is to identify and predict their response to causal environmental variables. However, most existing attempts rely on linear approaches based on correlation, which cannot apply in complex, nonlinear natural systems, because correlation is neither a necessary nor sufficient condition for causation. Applying empirical dynamic modelling that acknowledges nonlinear dynamics on nine subpopulations of tiger mosquitos from three neighbouring reef islets of the Raiatea atoll, we identified temperature, precipitation, dew point, air pressure, and mean tide level as causal environmental variables. Interestingly, responses of subpopulations in close proximity (100–500 m) differed with respect to their causal environmental variables and the time delay of effect, highlighting complexity in mosquito-environment causality network. Moreover, we demonstrated how to explore the effects of changing environmental variables on number and strength of mosquito outbreaks, providing a new framework for pest control and disease vector ecology.

Effects of a sex ratio gradient on female mate-copying and choosiness in Drosophila melanogaster

In many sexually reproducing species, individuals can gather information about potential mates by observing their mating success. This behavioral pattern, that we call mate-copying, was reported in the fruit fly Drosophila melanogaster where females choosing between 2 males of contrasting phenotypes can build a preference for males of the phenotype they previously saw being chosen by a demonstrator female. As sex ratio is known to affect mate choice, our goal was to test whether mate-copying is also affected by encountered sex ratios. Thus, we created a gradient of sex ratio during demonstrations of mate-copying experiments by changing the number of females observing from a central arena 6 simultaneous demonstrations unfolding in 6 peripheral compartments of a hexagonal device. We also tested whether the sex ratio experienced by females during demonstrations affected their choosiness (male courtship duration and double courtship rate) in subsequent mate-choice tests. Experimental male:female sex ratio during demonstrations did not affect mate-copying indices, but positively affected the proportion of both males courting the female during mate-choice tests, as well as male courtship duration, the latter potentially explaining the former relationship. As expected, the sex ratio affected female choosiness positively, and Drosophila females seem to have evolved a mate-copying ability independently of sex ratio, and a capacity to adapt their choosiness to male availability. This suggests that, as in many animal species, individuals, especially females, can adapt their mate choice depending on the current sex ratio.

Influence of Abiotic Factors on Flight Initiation by Asian Citrus Psyllid (Hemiptera: Liviidae)

Predicting the emergence and arrival of insect pests is paramount for integrated pest management. To achieve this goal, it is important to understand how abiotic factors influence pest dispersal behavior. We investigated the effects of abiotic conditions on flight initiation by the Asian citrus psyllid, Diaphorina citri Kuwayama. We first explored the effect of barometric pressure changes on flight initiation. We used a custom-made barometric chamber and observed the activity of D. citri as measured by the number of psyllids captured on yellow cardboard panels coated with adhesive. We found that psyllid flight initiation changed in response to variations in barometric pressure rather than to differences in stable pressures. Diaphorina citri were equally active at 1,009 mbar and 1,022 mbar. However, D. citri dispersed more as barometric pressure increased, and less when barometric pressure decreased. In a subsequent experiment, we manipulated temperature and relative humidity and observed how D. citri dispersed between citrus plants. Psyllids dispersal increased linearly with temperature. Changes in humidity did not affect dispersal of D. citri. Less than 1% of psyllids dispersed at 15 °C, compared with 7.7% at 21 °C and 27% at 25 °C. The minimal threshold for D. citri to initiate flight is estimated to be 16.5 °C. Collectively, our results provide an initial step toward developing predictive models of D. citri movement as influenced by abiotic factors.

Weather-dependent microhabitat use by Tetrix tenuicornis (Orthoptera: Tetrigidae)

For ectothermic animals, selection of a suitable microhabitat is affected by a combination of abiotic and biotic factors. Also important is the trade-off between those microhabitats with optimal microclimatic conditions and food availability vs. those with the lowest level of competition and lowest risk of predation. Central European species of groundhoppers (Orthoptera: Tetrigidae) live in locations with small-scale mosaics of patches formed by bare ground, moss cushions and vascular plants (grasses and forbs). Our research focused on the effects of selected weather components (current temperature, humidity, atmospheric pressure and sunlight) on specific microhabitat selection by adults (during the reproductive season) and by the last-instar nymphs (during the non-reproductive season) of the groundhopper Tetrix tenuicornis. Using experimental conditions, we determined that microhabitat use by T. tenuicornis is sex-specific and that microhabitat preference differs between adults and nymphs. We suppose that microhabitats are used according to groundhopper current needs in relation to each habitat's suitability for maintaining body temperature, food intake and reproductive behaviour. Microhabitat preferences were significantly associated with temperature and atmospheric pressure. Changes in atmospheric pressure signal changes in weather, and insects respond to increases or decreases in pressure by adjusting their behaviour in order to enhance survival. We propose that, under low atmospheric pressure, T. tenuicornis actively seeks microhabitats that provide increased protection from adverse weather.