Characterization of field-evolved pyrethrum resistance among Drosophila hydei populations in North Carolina sweet potato storage facilities

Drosophila hydei is a destructive pest of sweetpotato roots during long-term storage. The fly causes internal damage to the crop and is a mechanical vector of the black rot fungus (Ceratocystis fimbriata) which reduces  marketable yield in storage houses. Frequent insecticide applications are used to control fly populations, primarily pyrethrum/pyrethroids, which could lead to field-evolved resistance. Given the rapid reproductive cycle of D. hydei, the development of resistance is a major concern and careful, limited use of insecticides is critical in preventing reduced effectiveness over time. This work characterizes baseline susceptibility of D. hydei to pyrethrum among fly populations in various storage houses with different insecticide input practices and cultural control of cull piles, which are thought to be a persistent source of infestations at the facility level. It is expected that higher resistance to pyrethrum in fly populations found in storage houses that primarily rely on frequent pesticide sprays. This work will provide an increased understanding of how pyrethrum spraying impacts D. hydei populations and provides a basis for future modeling efforts that includes aspects of resistance into disease epidemiology.