BRUCHUS-PISORUM L (COLEOPTERA, BRUCHIDAE) CONTROL BY A KNOCKDOWN PYRETHROID IN FIELD PEAS

In field trials, a single spray of cypermethrin applied to plots in a field pea crop at the rate of 40 g a.i. ha-1 and endosulfan (350 g a.i. ha-1) reduced damage by Bruchus pisorum L. (Coleoptera: Bruchidae) from 11% in unsprayed peas to 4%; peas sprayed with methomyl (340 g a.i. ha-1) or fenvalerate (40 g a.i.ha-1) suffered 6% and 8% damage respectively. In laboratory bioassays, cypermethrin acted by knocking down adult beetles exposed to pea leaves treated with cypermethrin at field rates; residues of 0.4 mg cypermethrin kg-1 fresh pea leaves caused 90% knockdown, but the beetles regained mobility when removed from contact with treated leaves. By extrapolating the cypermethrin bioassays to field results, we conclude that cypermethrin acts as a knockdown insecticide against pea weevil in the field. We conclude that cypermethrin is the most suitable of the insecticides tested for pest management in pea crops because of its relative persistence, and its activity against both Bruchus pisorum and another pest of peas, Helicoverpa punctigera.