Composition, Seasonal Abundance, and Parasitism of Liriomyza (Diptera: Agromyzidae) Species on Lettuce in Arizona

Abstract

Liriomyza trifolii (Burgess) and L. sativae Blanchard were the leafminer species found in commercial and experimental plantings of lettuce in the Yuma Valley, AZ. L. trifolii was the dominant species observed in commercial lettuce fields in fall surveys, although populations did not reach damaging levels. In experimental plots, L. sativae was the principal species observed. The sharp contrast in Liriomyza species composition between lettuce grown in commercial and experimental plots was likely a reflection of pesticide-use patterns in commercial lettuce fields. Seasonal abundance and parasitism of leafminers in experimental plantings of lettuce from 1990 to 1992 varied with temperature and planting date. Adults, active larvae, and mines with dead or parasitized larvae were most abundant during the fall growing season. Edible leaves and heads were not mined at harvest. Populations in winter and spring plantings occurred at relatively low densities, likely in response to cooler temperatures and parasitism. The parasitoid complex associated with Liriomyza in fall lettuce primarily consisted of Opius spp. and Chrysocharis parksi Crawford, whereas Diglyphus spp. occurred at lower densities. Natural suppression of leafminer populations by parasitoids and other mortality factors appeared to be important for maintaining Liriomyza populations below damaging levels.