Effects of cyromazine and abamectin on the pea leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) and its parasitoid Diglyphus isaea (Hymenoptera: Eulophidae) in potatoes

The pea leafminer, Liriomyza huidobrensis (Blanchard), arrived in Israel almost a decade ago. Although adults are resistant to insecticides, growers treat fields with translaminar insecticides (abamectin and cyromazine) after they see large numbers of adults. Field trials were conducted for 2 years in potatoes (Solanum tuberosum L.) to evaluate the effects of a single,properly timed, application of these two insecticides on L. huidobrensis and its eulophid parasitoid, Diglyphus isaea Walker. Abamectin and cyromazine were applied at recommended held rates once, early in the growing season. Yellow sticky traps were used to monitor adult population levels, and leaf samples were used to monitor larval population levels. Cyromazine residues were monitored within the potato plants by a gas chromatograph-mass spectrometer. Both insecticides significantly reduced leafminers as compared to non-treated control; however, cyromazine was significantly more effective than abamectin. Similarly, parasitoid populations from both insecticide treatments were significantly reduced as compared to the non-treated control; however, parasitoid populations from abamectin treated plots recovered sooner than in cyromazine treated plots. Cyromazine residues in the plant declined over time, with a half-life of approximate to 1 wk. Implications of these results on management practices are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.