Bt-resistant European corn borers and Nosema pyrausta: Implications for resistance management

Interactions of Nosema pyrausta Paillot (Microsporida: Nosematidae) in Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae), resistant and susceptible to the Bt protein Cry1Ab were studied. Differences in survival and developmental rate due to Cry1Ab exposure and N. pyrausta infection were quantified. Delayed development due to feeding on Cry1Ab has the potential to accelerate resistance evolution by precluding random mating. Resistant O. nubilalis infected with N. pyrausta were more susceptible to Cry1Ab than uninfected resistant O. nubilalis. Partially and fully resistant N. pyrausta-infected O. nubilalis exposed to Cry1Ab experienced reduced survival and weight compared with uninfected O. nubilalis. Encountering N. pyrausta in combination with Cry1Ab in late instars negatively impacted weight and development of resistant O. nubilalis, and killed susceptible O. nubilalis. These experiments illustrate the potential of N. pyrausta to influence resistance evolution by delaying development, and increasing susceptibility to Cry1Ab in resistant and susceptible O. nubilalis.