Monitoring insecticide resistance in western flower thrips (Frankliniella occidentalis) populations in fruiting vegetable production systems

The western flower thrips (Frankliniella occidentalis (Pergande), “WFT”) is a key pest of fruiting vegetables, causing major crop losses through direct feeding and oviposition, and indirect damage by vectoring tomato spotted wilt virus (TSWV). Due to heavy reliance on a limited number of effective insecticides as a primary control strategy, the continued development of insecticide resistance in WFT poses a significant management challenge. Notably, WFT has developed resistance to spinetoram, one of the most widely used and effective insecticides for WFT management in tomato and peppers. Understanding the temporal and spatial status of insecticide resistance in WFT populations across agroecosystems is critical for developing sustainable management programs.

In this study, we screened WFT populations from key crop hosts in the spring, such as wheat and strawberries, and from tomato and pepper fields across the state. Populations were subjected to laboratory bioassays using diagnostic doses of commonly used insecticides to estimate resistance

levels. Additionally, molecular analyses were conducted on WFT populations from regions with known low, medium and high resistance to spinetoram to assess resistance allele frequency across spatial and temporal scales. Knowledge of resistance levels and allele frequencies will support informed decision-making regarding insecticide rotation with different modes of action. Furthermore, understanding the prevalence and change in the frequency of spinetoram-resistant alleles in populations from early-season crop hosts and within season fruiting vegetables will help develop integrated resistance management strategies (such as crop rotation and spatial arrangement of crops) to mitigate resistance impacts.