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

Diet choice tests were conducted to examine the effects of Bacillus thuringiensis Berliner on larval feeding behavior of Dipel-resistant and susceptible strains of European corn borer, Ostrinia nubilalis (Hubner). Larvae (first through fourth instars) were presented an untreated standard diet and three diets incorporating different concentrations of a commercial formulation of B. thuringiensis, Dipel ES(TM). Significantly higher proportions of susceptible and resistant larvae were found on the control diet compared to the proportions recorded on any of the Dipel-treated diets. Soon after release (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 control diet increased steadily over 72 h after release, when 43 to 75% of larvae were found on the control diet. The proportion of third and fourth instars on the control diet also increased initially, with an equilibrium occurring 12 to 24 h later when 30 to 40% of larvae were found on the control diet. Both strains appeared to avoid the Dipel-treated diets and their responses were similar over different Dipel concentrations. The Dipel-resistant strain showed higher ability to avoid the treated diets than the susceptible strain.