Comparison of Sampling Methods for Estimating Western Flower Thrips Abundance on Lettuce

Abstract

Several relative sampling techniques (direct visual counts, beat pans and sticky traps) were compared to absolute counts (plant wash) to determine sampling reliability for estimating western flower thrips population levels in lettuce. In numerous plantings of experimental plots of head lettuce, the relative sampling methods indicated similar thrips population trends throughout the season and all relative estimates of abundance were significantly correlated with absolute densities. However, both relative methods could only account for a proportion of the adult thrips infesting head lettuce plants, where they estimated about 30% of the actual absolute population. For larvae, beat pan sample estimated about 18-20% of the actual population density, whereas direct visual counts accounted for less than 10% of the thrips present. Comparison of sampling methods in insecticide efficacy trials indicated that beat pan and direct visual counts did not always accurately estimate treatment differences for adult. For densities of thrips larvae however, beat pan and visual counts methods did consistently provide accurate estimates of treatment differences in efficacy trials. Overall, both beat pan and direct visual count procedures are reliable thrips sampling methods that will generally provide precise estimates of thrips abundance necessary in lettuce pest management programs. Furthermore, these methods, and the beat pan in particular, also may serve as effective research tools that provide reliable estimates of treatment differences.