Effect of parasitoids on lepidopterous pests in insecticide-treated and untreated tomatoes in western North Carolina
Campbell, C.D. | Walgenbach, J.F. | Kennedy, G.G.
Studies were conducted in 1988 and 1989 to identify the parastoid complex of lepidopterous pests of tomatoes in western North Carolina, and to assess the compatibility, of various insecticides with natural control of these pests. Trichogramma exiguum (Pinto & Platner) and T. pretiosum (Riley) were the primary egg parasitoids of Helicoverpa (= Heliothis) zea (Boddie) and Manduca spp. in 1988, whereas T. exiguum was the predominant species collected from H. zea and Trichoplusia ni (Hubner) in 1989. Parasitization of H. zea eggs on plants treated with endosulfan, methomyl, and Bacillus thuringiensis Berliner var. kurstaki did not differ significantly from the untreated control. However, egg densities were higher in synthetic insecticide treatments presumably because of disruption of predators in these treatments. Despite the low toxicity of esfenvalerate to Trichogramma spp. in laboratory bioassays, parasitization of H. zea and Heliothis virescens (F.) eggs in the field was significantly reduced on esfenvalerate-treated tomatoes. This decreased level of parasitization was attributed to an avoidance by Trichogramma spp, to pyrethroid insecticides, which was previously reported. Under the relatively low-density lepidopterous populations observed in these studies, the efficacy of specific insecticides against H. zea and T. ni was more important in preventing damage than the level of parasitization of these pests, because the treatment with the lowest level of parasitization (esfenvalerate + B. thuringiensis) had the lowest levels of fruit damage in both years.
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