Seasonal Abundance of Western Flower Thrips Populations in Desert Head Lettuce

Abstract

Studies were conducted from 2001-2004 to examine thrips abundance in multiple lettuce plantings throughout the growing season. Head lettuce was sampled periodically on untreated, 0.25 acre plots at various intervals from early September through March. Results clearly showed that thrips reproduction and development on desert lettuce is largely influenced by temperature. Thrips adults and larvae populations within each planting were consistently most abundant on lettuce planted in November and December where temperatures averaged 60-65 degrees F during the spring. Population development was at its lowest level in the October plantings, particularly during the cooler winter periods. This study demonstrates that western flower thrips populations are capable of reproducing and developing large densities on head lettuce under winter and spring growing conditions in the desert.