EVALUATION OF TRICHOGRAMMA-NUBILALIS AND BACILLUS-THURINGIENSIS IN MANAGEMENT OF OSTRINIA-NUBILALIS (LEPIDOPTERA, PYRALIDAE) IN SWEET CORN

A biological control program for European corn borer, Ostrinia nubilal is (Hubner), using Trichogramma nubilalis Ertle & Davis and Bacillus t huringiensis var. kurstaki was tested in plots of sweet corn 1990 and 1991. Trichogramma were released during the egg mass recruitment perio d of O. nubilalis to bracket the peak egg mass deposition period. One or two B. thuringiensis applications were targeted against host larvae that escaped T. nubilale parasitism in the egg stage. The European co rn borer phenology model adequately predicted the timing and shape of the adult flight and egg recruitment periods in 1990 and 1991. The rel eased Trichogramma parasitized 70 and 56% of the European corn borer e ggs in 1990 and 1991, respectively. In both years, <20% of the host eg gs hatched in the Trichogramma release plots, compared with 38-56% in the control plots. Total mortality of European corn borer from egg dep osition to sweet corn harvest was 94 and 92% in 1990 and 1991, respect ively. The stage structure of the European corn borer population at sw eet corn harvest in 1991 did not differ between the Trichogramma relea se and no release plots. The proportion of sweet corn ears free of Eur opean corn borer larvae varied with position of the plots relative to nearby sudangrass, and ranged between 0.7 and 0.9 in the release plots , compared with 0.6-0.65 in control plots in 1990 and 1991, respective ly.