Deciphering the effects of ecological factors on oviposition behaviour and their impacts on offspring performance

<p dir="ltr">Oviposition is an important factor of insect biology. By selecting oviposition sites, females can modulate offspring nutritional environment, density, infection risk, and exposure to microbes. These decisions shape offspring larval development and adult life history traits. To date, our understanding of how parental experience interacts with environmental factors to modulate oviposition behaviour and offspring performance is limited. My thesis investigated the effect of parental larval density, maternal infection status and the nutritional composition of the oviposition substrate on the oviposition behaviour of the vinegar fly <i>Drosophila melanogaster</i> (Diptera: Drosophilidae). I used full factorial experiments to measure oviposition behaviour and offspring performance in both choice and no-choice assays. Maternal larval density and infection status did not influence oviposition behaviour in no-choice assays, with flies laying most of their eggs in the yeast (Y)-biased substrates. However, for the first time, my study reports that maternal density and infection status modulate oviposition in choice assays. The nutritional composition of the rearing substrate and maternal status (i.e., density and infection status) also interacted to affect offspring development, fecundity and resistance to infection. Offspring developed quicker and had higher fecundity when reared in high protein substrates compared to those reared in high carbohydrate substrates. Maternal infection delayed developmental time of offspring larvae. Adult offspring from infected females had higher fecundity when reared in high protein substrate compared to those reared in high sugar substrate. Moreover, high protein content in larval rearing substrates positively influenced bacterial resistance in adults. Interestingly, the effect of rearing substrate was overridden by maternal immune priming, with higher resistance observed in offspring from infected mothers, regardless of the rearing substrate. My results confirm intergenerational effects of parental larval diet on offspring life history traits and metabolism. Overall, the data collected in this thesis suggest that the oviposition behaviour of <i>D. melanogaster</i> females is modulated by the interactions between the nutritional properties of the environment and maternal physiology (or experience), and affects offspring performance. Finally, the nutritional conditions experienced by females have intergenerational implications on fitness traits. This understanding is crucial for developing control methods for pest insects and conservation strategies to safeguard insect biodiversity.</p>