Impacts of three insecticides on the community structures wheat aphids and their predators in wheat field.
The community structure of aphids (Macrosiphum avenae [Sitobion avenae], Rhopalosiphum padi, Schizaphis graminum and Acyrthosiphon dirhodum [Metopolophium dirhodum]) and their predators (Coccinella septempunctata, Leis axyridis [Harmonia axyridis], Propylea japonica, Syrphus corollae [Eupeodes corollae], Epistrophe balteata [Episyrphus balteatus], Chrysopa septempunctata [Chrysopa pallens], Chrysopa sinica [Chrysopa nipponensis] and Erigonidium graminicolum) in wheat fields after treatment with pirimicarb, imidacloprid and omethoate was evaluated in field experiments conducted during 1999, in Zhengzhou, Henan, China. The results showed that the diversity indexes and evenness of wheat aphid and predator communities under pirimicarb and imidacloprid treatments were lower than those in non-sprayed plots and higher than those under omethoate treatment. On the other hand, the dominance and dominant concentrations under pirimicarb and imidacloprid treatments were higher than those in non-sprayed plots and lower than those under omethoate treatment. The results suggest that an effective management strategy should consist of a single spray of pirimicarb WP at 2.5 g a.i./667 m2 or imidacloprid WP at 1.0 g a.i./667 m2 at the early milking stage of wheat (critical period of wheat aphid damage) and suppression by natural enemies at other stages without insecticides to keep the aphid population under control.