Thesis: Transcriptome analysis of insecticide resistant Drosophila suzukii

Drosophila suzukii, also known as spotted wing Drosophila (SWD), is an
invasive agricultural pest that is a threat to berry production due to a
serrated ovipositor on female flies that enables them to lay eggs in
soft-skinned, ripening fruits. Currently, growers rely heavily on the use
of insecticides to manage D. suzukii. Over the past six years, insecticide
resistance has been detected in D. suzukii in California, but the
molecular mechanism underlying this adaptation is unknown. Therefore, we
sought to identify the molecular mechanism conferring insecticide
resistance in these pests. We generated isogenic lines from
field-collected resistant populations and sequenced the transcriptomes of
two pyrethroid- and two spinosad-resistant lines. In both
pyrethroid-resistant isogenic lines and one spinosad-resistant line, we
identified an overexpression of metabolic genes that have been previously
implicated in insecticide resistance in other insect pests. In the other
spinosad-resistant line, we observed an overexpression of cuticular genes
that have been linked to insecticide resistance. Additionally, we observed
decreased expression of the pyrethroid target gene, paralytic, in both
pyrethroid-resistant lines. Our findings enabled the development of
molecular diagnostics that can be used to monitor resistance development
in the field, specifically by monitoring overexpression of specific target
genes. Finally, long-read sequencing reveals transcriptome-wide changes in
the expression of different splice variant isoforms, suggesting that
alternative splicing can be an additional mechanism enabling insecticide
resistance. This study is the first to characterize the molecular
mechanisms of insecticide resistance in field-collected D. suzukii and
provides insights into how current management practices can be improved.