Características biológicas de Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) parasitando ovos de Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Abstract

The bollworm Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) did not occur in Brazil until recently. The introduction and its distribution in most part of Brazil have caused considerable losses to attacked crops. Thus, the parasitism of H. armigera eggs by a Brazilian commercial strain of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) was studied regarding the effect of: egg developmental age (0-12, 24-36 and 48-60 h), egg densities (15, 20, 25 and 30 eggs per female), and different temperatures (18, 21, 24, 27, 30 and 33 oC) on the parasitoids biology. Higher rates of parasitism was obtained in H. armigera eggs with up to 36 h old and when offered 20 eggs per female. Lower temperature threshold and thermal requirement for egg to adult development was 10.3 °C and 130.38 GD, respectively. The increase of temperature directly reduces parasitoid development durations from 18.67 to 6.10 days and the mean generation time (T) from 20.9 to 7.5 days when reared at 18 and 33 oC, respectively. The net reproductive rate (R0) did not differ between 21 and 27 °C; while the intrinsic rate of population increase (rm) kept increasing up to 30 °C. The greater number of host egg parasitized was observed in the first day of adult stage across all studied temperatures, except at 30 °C when the highest parasitism took place in the second day. The female longevity and the parasitism rate decreased with increasing temperatures. The higher parasitism was found at 24°C. The results indicate that the Brazilian strain of T. pretiosum has potential to be used as an applied biological control agent of the studied pest across the most areas of occurrence in Brazil.