Residual action of pesticides sprayed on corn plants on Trichogramma pretiosum

ABSTRACT The objective of this study was to evaluate the residual effect of nine pesticides and a fungicide/acaricide on the parasitoid Trichogramma pretiosum Riley, 1879, in field conditions. Corn plants were sprayed with pesticides up to the runoff point three days before assembling the bioassays. Anagasta kuehniella (Zeller, 1879) eggs were offered in blue cardstock cards, individualized within the cages. The newly emerged adults of T. pretiosum were released in the proportion of 1.6 female per egg of the alternative host. Releases of the parasitoids were performed at 3, 10, 17, 24, and 31 days after spraying the plants. The pesticides were classified by their persistence, following the scale proposed by IOBC. The results showed that the commercial/active ingredients (kg or L ha.-1), used in corn, beta-cyfluthrin (0.10), cypermethrin (0.08), chlorpyrifos (1.00), lambda-cyhalothrin 50 (0.15), methomyl (0.60), sulfur (1.00), and thiodicarb (0.15) were moderately persistent (class 3; 6-30 days of harmful action) and lambda-cyhalothrin 250 (0.10), lambda-cyhalothrin + thiamethoxam (0.25), and spinosad (0.10) were persistent (Class 4; > 31 days of harmful action) on T. pretiosum.