Epsilon Open Archive

Abstract

The last two decades have seen considerable research effort dedicated to understanding the molecular basis of insect olfaction. There are, however, many knowledge gaps, especially when it comes to how insects detect different olfactory stimuli from the environment. In this thesis I aim to deepen our understanding of the detection of social and environmental cues in two insect species.

Codling moth, Cydia pomonella, is the foremost pest of apple. Following an initial identification of the chemoreceptors in male and female antennae, we provided an extensive annotation, transcript abundance quantification and repertoire completion of each of the three main chemoreceptor gene families. These results evidenced the importance of the candidate pheromone receptors (PRs), OR1, OR6 and OR3. Then, by heterologous expression in Drosophila melanogaster flies we functionally characterized some of these receptors. These experiments demonstrated that CpomOR3 is highly specific and sensitive toward pear ester, a strong kairomone and pheromone synergist of codling moth, which had not previously been found in apples. These results inspired a refined analysis of apple headspace which demonstrated the presence of this kairomone in apples. Furthermore, we show a putative microbial origin of this compound. We also characterized CpomOR6 as the receptor of the pheromone antagonist codlemone acetate, and CpomOR19 as a receptor tuned to indanones. Additionally, we provide a step-by-step description of the protocol to produce and characterize insect ORs and PRs through heterologous expression in D. melanogaster. Finally, we identified chemoreceptors from three tortricids and predict their function based on our results from codling moth. In addition, we investigated the common fruit fly D. melanogaster. In this species, an olfactory gene, OR69a, is expressed as two alternatively spliced variants: OR69aA and OR69aB. Through means of single sensillum recordings (SSRs) we characterized the non-overlapping response of both variants, showing that OR69aA responds to several plant compounds, while OR69aB detects a novel, long-range female-produced pheromone.

Together our results show that insects possess elegant ways to detect species-specific signals and the habitat cues that interact with those signals.