IMPORTANCE OF PLANT SIZE, DISTRIBUTION OF EGG MASSES, AND WEATHER CONDITIONS ON EGG PARASITISM OF THE EUROPEAN CORN-BORER, OSTRINIA-NUBILALIS BY TRICHOGRAMMA-OSTRINIAE IN SWEET CORN

Trichogramma ostriniae (Hym: Trichogrammatidae), an egg parasitoid of the European corn borer, Ostrinia nubilalis (Lep: Pyralidae), were rel eased into sweet corn (Zea mays L.) fields to study the effects of wea ther, plant size and distribution of egg masses on egg parasitism by t he wasp. Sentinel European corn borer eggs were stapled onto leaves lo cated in the upper, middle and lower third of sweet corn plants 5 to 3 5 meters away from the wasp release point in either a radial or grid m anner. Weather conditions and plant architecture were monitored during the experiments. Logistic regression was used to analyze the data. Th e results indicated that percentage of eggs parasitized was negatively related to an increase in leaf area as well as an increase in distanc e eggs were located from the point of release of wasps. Eggs distribut ed on plants at different directions from the release point received d ifferent levels of parasitism. Eggs that were stapled onto leaves in t he upper third of a corn plant received much less parasitism than thos e on the middle and lower third of the plant. Higher mean temperature adversely affected the level of parasitism during hotter times of the season and conversely, lower temperatures (< 17 degrees C) reduced the egg parasitism during cooler times of the season. The longer the expo sure of eggs to wasps, the higher the level of egg parasitism. However , the levels of egg parasitism for 2 day's exposure were almost the sa me as that for 3 day's exposure due to the limited longevity and egg-l aying behavior of the wasp. These results suggest that inundative rele ases of T. ostriniae should be made every two to three days, with mult iple release points per hectare. In addition, weather conditions and p lant architecture, especially temperature, plant height and leaf area must be taken into consideration to optimize levels of parasitism.