Distribuição de ovos de Plutella xylostella (L. ) (Lepidoptera: Plutellidae) e o parasitismo por Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) / Egg distribution of Plutella xylostella (L. ) (Lepidoptera: Plutellidae) and the parasitism by Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae)

ABSTRACT

Oviposition site preference of Plutella xylostella (L.) and the parasitism by Trichogramma pretiosum Riley on cabbage plants at pre- and post-head formation were investigated in commercial cabbage field. Groups of six plants were randomly caged. In each cage three pairs of 24h-old P. xylostella moths were released, followed by 1,200 T. pretiosum females released 12h later. After 48h from parasitoid release, plants were harvested and fully inspected with the oviposition mapped according to the leaf position and their parts (basal, median and border) and upper and bellow leaf surfaces. Moth oviposition and egg parasitism were equally distributed across the plant leaves at the pre-head formation stage. At this stage, the basal part and the upper leaf surface were the preferred places for oviposition and egg parasitism, respectively. Cabbage plants at the post-head formation stage exhibited greater oviposition and egg parasitism in the inner leaf attached to the head. At this stage, the leaf border and the upper leaf surface were the preferred places for oviposition and egg parasitism, respectively. The infestation of P. xylostella on cabbage can be determined by egg counting at the pre- and post-head formation stages at the basal part of the leaves or at the border of the leaf attached to the head, respectively. And, in both plant stages parasitized eggs by T. pretiosum are more likely to be found at the upper leaf surface.