Chlorpyrifos spraying of no-tillage corn during tasselling and its effect on damage byHelicoverpa zea(Lep., Noctuidae) and on its natural enemies

Corn plants were twice sprayed at 3-day intervals during tasselling to evaluate the effect of chlorpyrifos on ear damage by H. zea and also on the populations of the natural enemies associated with this moth. The abundance of H. zea eggs and larvae and of predators on the whole plant, the egg parasitism by Trichogramma pretiosum Riley and the percentage of injured ears were sampled weekly. Chlorpyrifos did not show any significant effect on population levels and on ear damage by H. zea. Natural parasitism of eggs ranged from 52 to 75% and did not differ between treated and untreated plots; furthermore, the percentage of non viable eggs and adult emergence were not influenced by insecticide application. Among the predators found in the plots, Doru luteipes was not affected by spraying, whereas the abundance of Orius sp. decreased 21 days after insecticide application. The frequency of the ant Pheidole sp. was not affected by chlorpyrifos; however, foraging activity of Crematogaster sp. on treated plots was rapidly reduced and remained low during the following 2 weeks. The small number of damaged ears suggests that the insecticide did not affect the efficiency of the natural enemies of H. zea.