Effect of insecticide applications and indigenous parasitoids on population trends of Liriomyza trifolii in gerbera greenhouses

Abstract

The seasonal occurrence of Liriomyza trifolii adults in gerbera greenhouses was monitored with yellow sticky traps. Dead L. trifolii larvae collected from gerbera leaves were dissected to determine their mortality factors. The mortality, rate of parasitism, and survivorship were estimated using the observed numbers of dead, parasitized, and living L. trifolii larvae. Six eulophid species were found in the greenhouses as larval parasitoids of L. trifolii. Neochrysocharis formosa and Chrysocharis pentheus were dominant, followed by Diglyphus albiscapus. Routine surveys revealed low parasitism (0%-1.3%) in conventional greenhouses where non-selective insecticides were applied frequently. After insecticide applications were stopped in these greenhouses, the L. trifolii population increased, followed by an increase in the rate of parasitism by indigenous parasitoids. Moreover, the larval mortality of L. trifolii also increased, presumably due to host-feeding by eulophid adults. These results indicate that eulophid parasitoids play an important role in suppressing L. trifolii population.