UC Davis

Tuta absoluta and Drosophila suzukii are two agricultural pest insects that have both rapidly spreadworldwide from their original ecosystems. Both cause serious economic losses, with the South American native T. absoluta targeting tomato agriculture and the Asian native D. suzukii targeting soft berry fruits. To inform current management strategies and prevent further introduction of these species, it is necessary to gain insights into current population structure and migration history of these species. Additionally, as T. absoluta has yet to be detected in North America, effective molecular diagnostics are needed to improve quarantine and monitoring efforts. In chapter one, we sequenced whole genomes of hundreds of D. suzukii samples collected worldwide. We identified two major population clusters in the United States and found that West coast D. suzukii populations originated from a combination of migration events from Hawaii and Asia. We saw no strong loss in genetic diversity in invasive populations relative to Asian populations, suggesting ongoing migration is alleviating any bottleneck effects. In chapter two, we sequenced dozens of whole genomes of T. absoluta across Latin America and Spain and found three populations in Latin America. Using population simulation approaches, we found that these populations diverged prior to human agriculture of tomatoes. Additionally, we detected signals of selective sweeps near genes relevant to insecticide resistance and metabolism. In chapter three, we developed two molecular diagnostics to distinguish T. absoluta from two morphologically similar species already present in the United States. The probebased quantitative PCR diagnostic can differentiate between T. absoluta, Phthorimaea operculella, and Keiferia lycopersicella using a thermocycler, while the RPA-Cas12a diagnostic can identity presence of T. absoluta in an isothermal reaction with minimal lab equipment requirements. We expect that these analyses and genomic resources will be of use to the agricultural research community in developing new strategies for controlling T. absoluta and D. suzukii.