Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2009
Publication Date: 1/11/2010
Citation: Lopez, M.D., Sumerford, D.V., Lewis, L.C. 2010. Nosema pyrausta and Cry1Ab-incorporated Diet Led to Decreased Survival and Developmental Delays in European Corn Borer. Entomologia Experimentalis et Applicata. 134(2):146-153. Interpretive Summary: The control of yield-reducing caterpillar pests of U.S. crops costs 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. Natural enemies may further delay resistance to Bt corn either by directly killing or delaying the development of resistance caterpillars. The enhancements offered by natural enemies of the European corn borer will improve the efficiency of refuge strategies and therefore offer greater cost savings to corn producers.
Technical Abstract: The high dose/refuge strategy for delaying evolution of resistance to Bacillus thuringiensis (Bt) corn relies on random mating between heterozygous-resistant European corn borers, Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae), and susceptible O. nubilalis from the refuge. However, differences in developmental rate due to feeding on Bt corn, or infection with the microsporidium Nosema pyrausta Paillot (Microsporida: Nosematidae) may result in assortative mating. Developmental delays and mortality caused by infection with N. pyrausta and feeding on Bt were quantified alone and in combination in Cry1Ab-resistant and susceptible O. nubilalis. Feeding on Cry1Ab-incorporated diet significantly increased number of days from hatch to pupation and decreased survival in the resistant population. Infection with N. pyrausta increased mortality and lengthened development in both the resistant and susceptible populations. The combination of Cry1Ab-incorporated diet and infection with N. pyrausta in resistant O. nubilalis lengthened development, and increased mortality to a greater extent than either factor alone. Greater larval delays of resistant O. nubilalis feeding on Bt corn could lead to temporal isolation from adults emerging from refuge corn. The resulting assortative mating would hasten the evolution of resistance. Developmental delays due to infection with N. pyrausta may increase the likelihood of mating between resistant and infected susceptible adults emerging from refuge corn, producing infected offspring that are also more susceptible to Bt corn.