(1st Place) Improving onion thrips, Thrips tabaci (Thysanoptera: Thripidae), surveillance in onion with a strategic sequential sampling plan

Onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae), is a significant economic pest of onion worldwide. Onion thrips reduce bulb yields through feeding injury on leaf tissue and the transmission of destructive plant pathogens. Current action thresholds based on the mean number of thrips per leaf have been used successfully to provide season-long thrips control, but with 1-5 fewer insecticide applications compared with a weekly spray program. While the adoption of this action-threshold based program has reduced costs, control decisions still depend upon significant fixed-sampling efforts, which can be a barrier to adoption. To address this issue, we developed a spatially-optimized sequential sampling plan using spatio-temporal thrips data collected during the 2021 and 2022 growing seasons.

The sequential sampling plan was designed using Taylor's power law and Wald's sequential probability ratio test (SPRT) to determine thrips population aggregation patterns and the likelihood ratio between the null (spray) and alternative hypotheses (no spray), based on the observed data, at each step of the sampling process. The goal of the sampling plan was to reduce the number of samples needed to optimize insecticide applications required while still maintaining effective control of onion thrips populations

Our results demonstrated that the sequential sampling plan was effective in reducing sampling effort required to estimate populations of onion thrips by up to 50% compared with the traditional fixed sampling approach. The greater level of surveillance of our plan also helped growers optimize insecticide applications without compromising control of onion thrips populations.