Date of Award
Doctor of Philosophy (PhD)
DEET (N, N-diethyl-m-toluamide) is the most broadly effective and widely used personal repellent available, yet we do not understand what makes it so effective. Even in well-studied species like Drosophila melanogaster flies and Aedes aegypti mosquitoes, many mysteries remain as to how DEET can affect behavior in these species. For example, Ae. aegypti mosquitoes are attracted to human arms. When an arm is covered in DEET, wild-type mosquitoes are not attracted to the arm, while mutant mosquitoes that lack the odorant receptor co-receptor (orco), approach the arm, but rarely bite. We investigated this orco-independent DEET repellency in Ae. aegypti and found that these mosquitoes can sense DEET with their tarsi as well as their proboscis. The tarsi are required for mosquitoes to be repelled after contact with a DEET-treated arm. The proboscis is required for the rejection of DEET-laced liquid food. These results suggest that DEET acts on multiple sensory modalities to repel insects. Both this work and most prior literature has focused on studying how DEET affects Arthropods, yet one of the major open questions in the field is how DEET can be effective across so many different species. To identify genes and neurons required for DEET-sensitivity outside of Arthropoda, we turned to the nematode C. elegans. Here, we demonstrated that DEET affects chemotaxis to some odors but not others. We used this behavior as the basis for a forward genetic screen, and identified two genes as candidates required for complete DEET-sensitivity. We identified a natural isolate of C. elegans that was also resistant to DEET, and found that it contains a large deletion in one of the hits from our screen, the G protein-coupled receptor str-217. This gene is required for DEET-sensitivity in both wild-type and wild isolate strains. str-217 is expressed in a single pair of chemosensory neurons called ADL, which are required for complete DEET sensitivity, and respond to DEET as assayed by calcium imaging. Although we identified additional sensory neurons that respond to DEET, their behavioral contributions are unknown. Both ADL and str-217 are required for a specific, DEET-induced behavior during chemotaxis and exploration: an increase in average pause duration. Through optogenetic stimulation of ADL, we demonstrated that ADL activity alone is sufficient to increase average pause duration. Taken together, these experiments provide insights into the genetic and neural mechanisms underlying DEET-sensitivity in C. elegans, and allow for comparisons across Protostomes. We also establish C. elegans as a model non-Arthropod species for further investigation into the effects of DEET.
Dennis, Emily Jane, "Multi-Modal Effects of the Repellent Deet Across Protostomia" (2018). Student Theses and Dissertations. 437.