Date of Award
Spring 2023
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Molecular, Cellular, and Developmental Biology
First Advisor
Carlson, John
Abstract
Drosophila suzukii, also known as the spotted wing Drosophila, is an agricultural pest of fruits that has caused severe economic losses for a wide variety of fruit industries. It invaded the United States and Europe in 2008, and since then it spread at an unprecedented rate. D. suzukii devastates many fruit crops, including strawberries, raspberries, and blueberries. Unlike most Drosophila species, including D. melanogaster, which lay eggs in overripe fruit, D. suzukii has an egg-laying preference for intact ripe fruit and thus it is destructive. D. suzukii females possess an enlarged saw-like ovipositor, the egg-laying organ, that is able to pierce the skin of intact fruits and insert eggs inside the fruits. But little is known about the sensory mechanisms underlying its different egg- laying preference. This disparity of the egg-laying preference provides an excellent opportunity for comparative studies about how sensory systems evolve to recognize suitable egg-laying sites, which remains poorly understood, taking advantage of the vast accumulated knowledge and genetic tools of D. melanogaster. We show that D. suzukii has undergone a variety of changes in sweet taste sensation. D. suzukii has a weaker preference than D. melanogaster for laying eggs on substrates containing all three primary fruit sugars: sucrose, fructose, and glucose. Major subsets of D. suzukii taste sensilla have lost electrophysiological responses to sugars. Expression of several key sugar receptor genes is reduced in the taste organs of D. suzukii. By contrast, certain mechanosensory channel genes, including nompC, are expressed at higher levels in the taste organs of D. suzukii, which has a higher preference for stiff substrates. In addition, we find that D. suzukii responds differently from D. melanogaster to combinations of sweet and mechanosensory cues. We also find that changes in bitter taste perception have accompanied this adaptation. We show that bitter-sensing mutants of D. melanogaster undergo a shift in egg-laying preference toward ripe fruit. D. suzukii has lost 20% of the bitter-sensing sensilla from the labellum, the major taste organ of the head. Physiological responses to various bitter compounds are lost. Responses to strawberry purées are lost from two classes of taste sensilla. Egg laying is not deterred by bitter compounds that deter other species. Profiling of labellar transcriptomes reveals reduced expression of several bitter Gr genes (Gustatory receptors). These findings support a model in which bitter compounds in early ripening stages deter egg laying in most Drosophila species, but a loss of bitter response contributes to the adaptation of D. suzukii to ripe fruit. Thus, the two species differ in sweet sensation, bitter sensation, mechanosensation, and the integration of sweet sensation and mechanosensation, which are all likely to contribute to the differences in their egg-laying preferences in nature. These results lead to a better understanding of the neural mechanisms underlying the unusual egg-laying preference of D. suzukii. And they could be useful in devising novel, environmentally- safe strategies for the control of insect pests.
Recommended Citation
Wang, Wanyue, "Sensory Changes Underlying the Egg-laying Preference Shift of the Agricultural Pest Drosophila suzukii" (2023). Yale Graduate School of Arts and Sciences Dissertations. 908.
https://elischolar.library.yale.edu/gsas_dissertations/908
