Seasonal abundance of hymenopteran parasitoids of the leafminer Chromatomyia horticola (Diptera: Agromyzidae) and the impact of insecticide applications on parasitoids in garden pea field

Abstract

The seasonal abundance of hymenopteran parasitoids reared from the agromyzid leafminer Chromatomyia horticola was monitored on garden pea in Shizuoka, central Japan, for 17 months between 2004 and 2005. The leafminer was abundant during the cool seasons (December to May) but parasitoid populations generally lagged behind the leafminer by approximately two months. Twenty-one parasitoid species were reared from C. horticola, and the most abundant parasitoid species were Diglyphus isaea, D. minoeus and Chrysocharis pentheus, comprising ca. 90% of the total number caught. Diglyphus isaea and D. minoeus were abundant during the cool season (December to May), while C. pentheus was abundant in the warm season (May to June). Other common parasitoid species were Dacnusa nipponica, Neochrysocharis formosa and Halticoptera circulus. The effects of two insecticides, malathion and tralomethrin, on parasitoid populations were investigated both in the cool and warm seasons. The insecticides caused a reduction in the density of most parasitoid species for at least one month and resulted in resurgence of the leafminer. However, the density of H. circulus increased after insecticide applications, suggesting that this parasitoid was tolerant to both insecticides but H. circulus could not reduce C. horticola populations when insecticide applications were made to the crop. These studies provide insight into the development of integrated control strategies of leafminer pests in field and glasshouse crops.