Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/21/2010
Publication Date: N/A
Citation: Interpretive Summary: The control of yield-reducing caterpillar pests of U.S. crops cost growers millions of dollars each year. Bacillus thuringiensis (Bt) corn has been a valuable tool for controlling caterpillar pests. Resistance management strategies have successfully delayed resistance in the European corn borer to Bt corn. Insect diseases have the potential to delay resistance to Bt corn either by directly killing or delaying the development of resistance caterpillars. However, diseases that change the timing of adult emergence may make it more likely that Bt-resistant females mate with Bt-resistance males. The enhancements or detriments offered by insect diseases of the European corn borer will impact the efficiency of refuge strategies and therefore will affect cost savings to corn producers.
Technical Abstract: Infection with Nosema pyrausta Paillot (Microsporida: Nosematidae) lengthens developmental period of Bt-susceptible Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae) to a similar extent as feeding on Cry1Ab-incorporated diet in Cry1Ab-resistant O. nubilalis, and these two factors combined lengthen developmental period further than either alone. Differential developmental rates may increase the likelihood of resistant adults mating with infected susceptible or infected resistant partners, which would violate the high dose/refuge strategy assumption of random mating. Resistant O. nubilalis mating with infected susceptible or infected resistant partners would produce partially- and fully-resistant offspring, respectively, infected with N. pyrausta. To investigate the impacts on the progeny of such matings, test crosses were set up to produce partially- and fully Cry1Ab-resistant O. nubilalis offspring transovarially infected and not-infected with N. pyrausta, which were exposed to Cry1Ab toxin at doses of 0, 3, or 30 ng per cm-squared for 7 days. Transovarial infection with N. pyrausta significantly decreased 7 day survival of partially and fully-resistant O. nubilalis feeding on 30 ng/cm2 Cry1Ab. In addition, N. pyrausta infection delayed larval development (as measured by weight) of partially- and fully-resistant O. nubilalis feeding on 3 and 30 ng per squared-cm Cry1Ab. Interactions of target pests with natural enemies have the potential to impact evolution of resistance. Nosema pyrausta-infected O. nubilalis are more strongly affected by feeding on Bacillus thuringiensis (Bt), and would be less likely to survive to adulthood to pass on resistance to the next generation. This indigenous microsporidium may work to delay evolution of resistance in O. nubilalis by lowering their ability to survive on Bt.