Nothing but the ‘pollen’ truth: Bridging field and laboratory studies to understand western flower thrips host preference and abundance.

Western flower thrips (Frankliniella occidentalis) is the main vector of impatiens necrotic spot virus, which has recently caused substantial economic losses in California lettuce production. Understanding thrips host selection and feeding preferences can be utilized for developing effective management strategies, yet these aspects remain poorly understood in the region. Initial field surveys of flowers from 24 plant species across the Salinas Valley revealed iceplant (Carpobrotus edulis) and strawberry (Fragaria × ananassa) flowers consistently supported high thrips populations, including F. occidentalis and Thrips tabaci (onion thrips) that were confirmed using both molecular and morphological tools. Building off this initial work, we sought to investigate the feeding preference and fecundity of F. occidentalis when fed on pollen collected from iceplant, strawberry, and shortpod mustard (Hirschfeldia incana), which was determined to be a moderate host for thrips from the initial field surveys. Commercial pine pollen was also included as a control. Laboratory choice assays and reproductive trials were performed and analyzed using one-way ANOVA and Tukey’s HSD for pairwise comparisons. We found that F. occidentalis strongly preferred iceplant pollen and had higher fecundity compared to strawberry. Consistent with field observations, F. occidentalis had an intermediate preference for shortpod mustard pollen in laboratory assays. Our ongoing trials indicate iceplant is a highly favorable host plant, potentially due to greater nutritional value of the pollen itself. This work provides insight into thrips behavior and host preferences, which in turn, could assist in improving vector management strategies in the region.