Influência de três cultivares de milho, Zea mays Linnaeus e do numero de ovos de Helicoverpa zea (Boddie, 1850) (Lepidoptera: Noctuidae) no parasitismo destes por Trichogramma atopovirilia Oatman & Platner, 1983 e Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae)

Abstract

Laboratory studies aiming to evaluate the response of Trichogramma pretiosum and T atopovirilia to the increase of both host and parasitoid densities to respectively 1, 3, 5 and 10 females, and 30, 60, 90, 120 and 150 eggs per vial demonstrated that in densities above 90 eggs for T pretiosum and 120 for T. atopovirilia there was no mutual interference. In lower densities to both species, there was fewer eggs parasitised by female. Percent parasitism was lower with the increment ofegg density for both species. Field studies with three corn cultivars (BR 451, BR 400 and BR 205) under two planting schedules demonstrated that when ali cultivars were planted in the same date there was unsincronyzed flowering and no significant differences were found in both pest density and egg parasitism. On the otherhand, when planting dates were established as to synchronize flowering and therefore optimize chances ofparasitism, highervalue was found for BR 451 (62.4%), which differed from BR 400 (34.1%) cultivar. The BR 205 (47.0%) was intermediate among the other two cultivars. Physical, chemical and morphological factors of the cultivars acting isolated or in combination may have had influence in the results obtainedbut they were not measured.