FIELD ASSESSMENT OF TRICHOGRAMMA-BRASSICAE (HYMENOPTERA, TRICHOGRAMMATIDAE) AND BACILLUS-THURINGIENSIS FOR CONTROL OF OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE) IN SWEET CORN

Field studies conducted in 1992 and 1993 tested the efficacy of using commercially available Trichogramma brassicae Bezdenko and Bacillus th uringiensis to control Ostrinia nubilalis (Hubner) in sweet corn. Ship ped T. brassicae displayed. good biotic fitness (emergence rates, sex ratios, longevity, and fecundity) in 1992 and 1993, but release rates and emergence profiles of the parasitoids differed in the 2 yr. In 199 2, a total of 429,120 female parasitoids per hectare was released over 10 release dates. In 1993, a total of 163,680 female parasitoids per hectare was released over 10 release dates. Parasitoids dramatically a ffected the fate of O. nubilalis egg masses in both 1992 and 1993. O. nubilalis egg mass survival decreased by at least 45% in T. brassicae plots in both years. When all insect damage was considered, field rele ases of T. brassicae significantly improved ear quality in 1993 and in plots augmented with O. nubilalis egg masses in 1992. When an effect caused by T, brassicae was observed, the increase in percentage clear ears ranged from 9 to 17%. There was no significant interaction betwee n B. thuringiensis and T. brassicae treatments in 1992 and 1993. B, th uringiensis treatments alone had a significant impact on ear quality o nly when high O. nubilalis populations were present in 1992. The integ ration of B, thuringiensis and T. brassicae did not result in addition al insect control.