David BEN-YAKIR, David NESTEL and Michael CHEN,
Entomology Department, ARO, The Volcani Center, P.O. Box 6, Bet-Dagan, Israel 50250.

European corn borer (ECB) overwinters as a diapausing 5^th-instar larva in above-ground corn plant debris. Knowledge of factors affecting overwintering success, and the timing of spring emergence, can contribute to designing a control program for this pest. In Israel, overwintering ECBs pupate from early March to late April and emerge from early April to late May. During postdiapause development larvae in plant debris may be completely exposed or under various types of vegetation. These differences in ground cover create various climatic conditions for the developing larvae. In this study we determine the effects of various types of ground cover on the time and success of ECB’s spring emergence. Overwintering ECB larvae were dissected out of corn stalks during late Fall and early Winter. These larvae were placed in  artificial stalks  that enabled us to observe their development. These larvae were held outside, away from direct sunlight, until late February. Then, they were put on the ground of experimental plots with various types of cover. We compared their development under five types of covers (treatments): exposed, pea, sunflower, 30% shade and 60% shade. In the exposed plots ECB developed the fastest but 60-90% died before emergence. Under sparse vegetation (sunflower) or 30% shade ECB emergence took 1-2 weeks longer and about 50% emerged. Under thick vegetation (peas as green manure) or 60% shade ECB emergence was delayed 2-4 weeks and over 70% emerged. Thus, the density of ground cover was inversely correlated with developmental time and directly correlated overwintering success. Hot spells had a major role in reducing the overwintering success. Leaving late season corn fields exposed (without crops and with herbicides treatment) until May is expected to significantly lower the size of the ECB population that will overwinter successfully.