Parasitism in diversified agroecosystems: Phenology of Trichogramma minutum [Hymenoptera: Trichogrammatidae]

Parasitism of Ostrinia nubilalis egg masses by Trichogramma minutum was observed in maize-bare ground monocultures and polycultures of maize/bean/squash and maize/clover. Parasitism rates were 1.9 times higher in monocultures than in polycultures; seasonal phenology of parasitism, however, was similar in both. Parasitism first occurred during the late whorl/early tassel stage of maize; peak parasitism occurred during the mid to late tassel stage, and then dropped off rapidly. We speculate that direct predation of egg masses, and ammensal preemptive competition for egg masses by Coleomegilla maculata may have contributed to the decline in parasitism rates in both monocultures and polycultures during the latter part of the season.