Review

Authors: Monika Hilker, Hassan Salem, Nina E Fatouros...

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 () parents adjust the egg phenotype to the actual needs, () eggs themselves respond to environmental challenges, and () 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.

Topics: Female; Animals; Insecta; Adaptation, Physiological; Oviposition; Plants; Phenotype; Ovum

PubMed: 36266253
DOI: 10.1146/annurev-ento-120120-100746

Authors: Liwei Zhang, Huiwen Sun, Ewald Grosse-Wilde...

In a heterogeneous and changing environment, oviposition site selection strongly affects the survival and fitness of the offspring. Similarly, competition between larvae affects their prospects. However, little is known about the involvement of pheromones in regulating these processes. 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.

Topics: Animals; Female; Drosophila; Drosophila melanogaster; Oviposition; Pheromones; Drosophila Proteins; Larva

PubMed: 37098339
DOI: 10.1016/j.cub.2023.03.090

Authors: Philippe Reymond

Insect eggs deposited on plants constitute a threat that has led to the evolution of sophisticated defenses. The interactions between insect eggs and plants are governed by a diverse variety of chemicals that inform butterflies about suitable hosts, repel gravid females, alert plants about the presence of an egg, act as signal molecules to induce defenses, directly impair egg development, and indirectly attract egg parasitoids. In recent years, significant progress has been made on the chemical identification, perception and role of compounds associated with oviposition. Knowledge on the genetic basis of oviposition-induced responses is also accumulating. An emerging theme is that insect eggs are not passive structures on leaves but induce complex responses that result from million years of coevolution.

Topics: Female; Animals; Butterflies; Insecta; Oviposition; Plant Leaves; Plants

PubMed: 38069786
DOI: 10.2533/chimia.2022.914

Authors: Ruocong Tang, Rachel Busby, Willem J Laursen...

mosquitoes are major vectors of dengue, chikungunya, and other arboviral diseases. '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 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 , and humid air-activated Moist Cells upon . 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: -dependent Dry Cells act in parallel with -dependent Moist Cells to promote blood feeding, while oviposition site seeking is driven specifically by dependent Moist Cells. Together these findings reveal the importance of distinct hygrosensory pathways in blood feeding and oviposition site seeking and suggest dependent Dry Cells and dependent Moist Cells as potential targets for vector control strategies.

Topics: Animals; Humidity; Aedes; Oviposition; Female; Feeding Behavior; Mosquito Vectors; Sensilla; Receptors, Ionotropic Glutamate; Arthropod Antennae

PubMed: 39159375
DOI: 10.1073/pnas.2407394121

Authors: Zaid Khan, Björn Bohman, Rickard Ignell...

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.

Topics: Animals; Female; Aedes; Odorants; Oviposition; Smell; Larva; Water; Volatile Organic Compounds

PubMed: 37542293
DOI: 10.1186/s13071-023-05867-1

Authors: I C Dunn, P W Wilson, S Struthers...

1. The cuticle acts as a barrier to prevent microbial penetration of the eggshell. The reduction in the oviposition interval with selection for egg production and the activity of clock genes in the oviduct led to testing the hypothesis that the interval between successive oviposition of eggs would be related to the deposition of the cuticle.2. There was oviposition interval and cuticle deposition data from 2140 eggs from 5 White Leghorn pure lines for over 7 d. The association between oviposition interval and cuticle deposition was assessed using a random slopes model for each hen.3. The time of oviposition was 05:37 h:m, about 2.5 h after lights on. Differences in oviposition time between lines were significant (P=0.025). Oviposition interval was slightly greater than 24 h at 24:06 h:min with significant differences between lines (P = 0.003). The variance was low and the maximum difference between lines for oviposition interval was only 11 min. Cuticle deposition was 28.87ΔE*ab with no differences between lines.4. The number of eggs a hen laid had an effect on the oviposition interval (P = 0.004), being shortest in hens laying seven eggs (24:01 h:m) than those laying six (24:08) or five eggs (24:14).5. There was a significant positive association between cuticle deposition and oviposition interval (P = 0.007) with a minimal increase of 0.79 ΔE*ab in cuticle deposition for each additional hour of oviposition interval. Heritability for cuticle deposition in this study was 0.48 but heritability was not measurable for oviposition interval and was not different from zero for oviposition time.6. Combined with a difference between the top and tail of the distribution for cuticle deposition, there was evidence for a significant but relatively small relationship between oviposition interval and deposition of cuticle on the egg. This may have contributed to some reduction in cuticle coverage as the oviposition interval approached 24 h, but it seems unlikely that it was a major component.

Topics: Animals; Oviposition; Female; Chickens; Egg Shell; Ovum; Time Factors

PubMed: 39611433
DOI: 10.1080/00071668.2024.2425633

Authors: Ziye Wang, Delong Tan, Feifeng Wang...

Diaphorina citri is an important vector of Citrus Huanglongbing (HLB) disease. After feeding on young host plant shoots, the population of D. citri can increase significantly. Females also only lay eggs on young shoots. However, there are few studies on the mechanism of this phenomenon. Exogenous nutrient signals can affect the insulin signaling system of D. citri after feeding on young shoots. In this study, the expression of upstream factors DcILP1, DcILP2, and DcIR in the insulin signaling system of D. citri was upregulated after feeding on young shoots. After being silenced by RNA interference technology, the results showed that the number of oviposited eggs of D. citri was significantly decreased and the ovarian development was inhibited with severe vacuolation. In addition, detection using quantitative reverse transcription-polymerase chain reaction showed that the upstream regulatory gene DcRheb of the target of rapamycin (TOR) pathway and the downstream reproduction-related DcVg gene were also significantly downregulated. These results suggest that feeding upon young shoots may upregulate the expression levels of upstream factors DcILP1, DcILP2, and DcIR in the insulin signaling system. The signal will be through upregulating the expression of DcRheb, an upstream gene of the TOR signaling pathway. This in turn influences yolk metabolism, which eventually causes the ovaries of female D. citri to mature and therefore initiate oviposition behavior.

Topics: Female; Animals; Insulin; Oviposition; Citrus; Peptides; RNA Interference; Hemiptera; Plant Diseases

PubMed: 35510515
DOI: 10.1111/1744-7917.13048

Authors: Jorge R Rey, Sheila M O'Connell

We investigated the oviposition behavior of Ae. aegypti and Ae. albopictus. In particular we examined whether small-scale site characteristics and the presence of conspecifics or congeners altered oviposition by these mosquitoes. Various combinations of females of the two species were allowed to oviposit inside cages among either vegetation (potted plants) or structural components (wood and concrete blocks). Numbers of eggs deposited per female were compared between species, sides, and treatments. Most significant differences between treatments and species involved differences between single species and mixed species treatments. Ae. aegypti deposited more eggs/female in the vegetation side than in the structure side whereas the opposite pattern was evident for Ae. albopictus. Ae. aegypti females had higher frequency of skip oviposition than Ae. albopictus. An average of 63% of the containers in the two-species treatments contained eggs of both species, with more frequent joint occurrences observed in the treatment with three females of each species than in the treatments with one of each. Our results point to the existence of various interactions between gravid Ae. aegypti and Ae. albopictus females at or near the oviposition sites but further experimental work is necessary to fully characterize the interactions and their specific mechanisms.

Topics: Aedes; Animals; Female; Florida; Oviposition

PubMed: 24820572
DOI: 10.1111/j.1948-7134.2014.12086.x

Authors: Dannielle Kowacich, Eduardo Hatano, Coby Schal...

BACKGROUND

Gravid females assess the conditions of oviposition sites to secure the growth and survival of their offspring. Conspecific-occupied sites may signal suitable oviposition sites but may also impose risk due to competition or cannibalism at high population density or heterogeneous larval stage structure, respectively. Chemicals in the habitat, including chemicals emitted from other organisms, serve as cues for females to assess habitat conditions. Here, we investigated the attraction and oviposition preference of the Old World cutaneous leishmaniasis vector, Phlebotomus papatasi, to young and old conspecific stages, including eggs and evaluated the effect of a semiochemical associated with eggs and neonate larvae.

METHODS

Attraction and oviposition preference of Ph. papatasi to each of various life stages (eggs, first-, second-, third-, fourth-instar larvae, pupae and male and female adults) was investigated using cage and oviposition jar behavioral assays. Identification of organic chemical compounds extracted from eggs was performed using GC-MS and chemicals were tested in the same behavioral assays in a dose-response manner. Behavioral responses were statistically analyzed using logistic models.

RESULTS

Gravid Ph. papatasi females were significantly attracted to and preferred to oviposit on medium containing young life stages (eggs and first instars). This preference decreased towards older life stages. Dose effect of eggs indicated a hump-shaped response with respect to attraction but a concave-up pattern with respect to oviposition. Chemical analysis of semiochemicals from eggs and first-instar larvae revealed the presence of dodecanoic acid (DA) and isovaleric acid. Sand flies were attracted to and laid more eggs at the lowest DA dose tested followed by a negative dose-response.

CONCLUSIONS

Findings corroborated our hypothesis that gravid sand flies should prefer early colonized oviposition sites as indicators of site suitability but avoid sites containing older stages as indicators of potential competition. Findings also supported the predictions of our hump-shaped oviposition regulation (HSR) model, with attraction to conspecific eggs at low-medium densities and switching to repellence at high egg densities. This oviposition behavior is mediated by DA that was identified from surface extracts of both eggs and first-instar larvae. Isovaleric acid was also found in extracts of both stages.

Topics: Animals; Behavior, Animal; Female; Hemiterpenes; Larva; Lauric Acids; Male; Oviposition; Ovum; Pentanoic Acids; Pheromones; Phlebotomus; Pupa

PubMed: 32493498
DOI: 10.1186/s13071-020-04151-w

Authors: Mahmood R Nikbakhtzadeh, Yelissa Fuentes

Glyphosate is one of the most common herbicides used to control weeds in the USA. This herbicide can impact the mosquito life cycle through being carried to mosquito habitats by runoff. This study investigates the effects of glyphosate on the larval development and oviposition of a laboratory colony of Culex quinquefasciatus. Our experiments indicated that a concentration of 1 g/liter glyphosate was lethal to larval instars or the larvae impacted were either unable to molt to pupae or never emerged as adults. Larval instars exposed to 0.5 g/liter glyphosate experienced a similar impact; however, the larval stage was extended and pupation was considerably delayed. Mosquitoes oviposited in 0.5 g/liter glyphosate laid the same number of egg rafts as in water, but a considerably lower number of eggs exposed to glyphosate hatched as first instars. If gravid females laid their eggs in 1 g/liter glyphosate versus water, the difference between the 2 groups would be statistically significant and a very low number of eggs exposed to glyphosate could ever hatch into larvae. In an oviposition assay carried out in a cage with 3 choices of water, 0.5 g/liter, and 1 g/liter glyphosate, a higher number of egg rafts were laid in water, followed by 0.5 g/liter and 1 g/liter glyphosate concentrations, respectively. Our study indicated such a severe effect of glyphosate on all immature stages of Cx. quinquefasciatus that no adult could ever emerge.

Topics: Animals; Culex; Culicidae; Female; Glycine; Larva; Oviposition; Water; Glyphosate

PubMed: 35901290
DOI: 10.2987/22-7059