Developing parasitoid enhancement as a component of cole crop management

Three species of Lepidoptera (Trichoplusia ni, Pieris rapae, and Plutella xylostella) are responsible for much of the damage sustained by cole crops. Parasitoid wasps can reduce the amount of damage and the number of caterpillars within a field if they are not killed by applications of broad-spectrum insecticides. The integration of more selective chemical treatments and floral strips is being evaluated for effectiveness in suppressing the caterpillar complex of cole crops. Floral strips of sweet alyssum should increase parasitism rates because adult parasitoids rely on nectar for food. Two cabbage plots were established at each of three field sites in Ohio. One plot incorporated floral strips of sweet alyssum and one did not. Subplots within each field were treated with a pyrethroid or B.t., or were left untreated. Caterpillar populations were assessed weekly within each subplot. Late instar caterpillars were collected to determine parasitism rates. Average parasitism rate within each subplot ranged from 10 to 56% and was highest in P. xylostella and was generally higher in untreated plots. The presence or absence of floral strips did not have a significant impact on parasitism. However, the presence of floral strips had the significant benefit of a negative effect on the total number of caterpillars seen within the field at two out of three sites.