Larval feeding behavior of Dipel-resistant and susceptible Ostrinia nubilalis on diet containing Bacillus thuringiensis (Dipel ES (TM))

Diet choice tests were conducted to examine the effects of Bacillus thuring iensis Berliner on larval feeding behavior of Dipel-resistant and susceptib le strains of European corn borer, Ostrinia nubilalis (Hubner). Larvae (fir st through fourth instars) were presented an untreated standard diet and th ree diets incorporating different concentrations of a commercial formulatio n of B. thuringiensis, Dipel ES(TM). Significantly higher proportions of su sceptible and resistant larvae were found on the control diet compared to t he proportions recorded on any of the Dipel-treated diets. Soon after relea se (0.5 to 3 h), the occurrence of larvae on each of the diets was similar across different instars. The number of first and second instars on the con trol diet increased steadily over 72 h after release, when 43 to 75% of lar vae were found on the control diet. The proportion of third and fourth inst ars on the control diet also increased initially, with an equilibrium occur ring 12 to 24 h later when 30 to 40% of larvae were found on the control di et. Both strains appeared to avoid the Dipel-treated diets and their respon ses were similar over different Dipel concentrations. The Dipel-resistant s train showed higher ability to avoid the treated diets than the susceptible strain.