Utilization of microplot tents in determining insecticide efficacy of western flower thrips (Frankliniella occidentalis) on lettuce

Western Flower Thrips (Frankliniella occidentalis) are primary pests of lettuce in California by causing direct damage from feeding and from their role in vectoring plant viruses. Although the monitoring of insect control methods is often hampered by the migratory effects of the winged adults, installing mesh netting over lettuce plants prevents these effects, avoids emigration and immigration, and allows for a clearer comparison of treatments. Recently, using the caged lettuce technique at three different locations on the Central California coast, we determined the efficacy of Radiant SC on a controlled thrips population under field conditions. Within each replicate plot, three cages were installed over five lettuce plants. In addition, lettuce plants outside the cages received three applications whereas populations in Cage I received one application, Cage II received two applications, and Cage III received three applications. Evaluations were performed after each application. Differences in thrips populations among the treatments became noticeable after the first application for both nymphs and adults. It was apparent that the effect of insect migration on thrips densities within experimental plots were significantly different on caged versus open field plants. Further, these data show that one application of insecticide on caged plants was numerically comparable to three applications on open field plants. This result is shown to a greater extent for nymphs than for adults. The use of insect cages is beneficial in reducing the population count variability commonly associated with highly mobile pest species.