Movement behavior of third instar European corn borers, Ostrinia nubilalis, on Bt corn

Johnson, Holly
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University of Delaware
The European corn borer (ECB), Ostrinia nubilalis (Hübner), is a major lepidopteran pest of maize in the United States and Canada. One of the most effective control methods for ECB is the use of transgenic crops that encode for insecticidal crystalline (Cry) proteins that are derived from the soil bacterium Bacillus thuringiensis (Bt). The continued effective use of Bt corn relies on compliance with insect resistance management practices; where planting a small percentage of non-Bt refuge corn adjacent to or as seed blends within Bt corn fields provides a population of susceptible insects that can mate with rare resistant individuals. Little is known about how these non-Bt plant blends affect movement behaviors of ECB in the third instar, an intermediary stage where the larva begins to bore into corn stalks. The objective of my study was to assess and characterize the amount of movement off of infested plants in the field using a variety of five plant arrays containing lepidopteran Bt corn plants and non-lepidopteran protein marked refuge corn plants. Additional studies sought to determine the presence and persistence of three different Bt Cry proteins in third instars using monoclonal ELISA test strips. Based on two years of field movement studies I found that the range of third instars moving off of an infested plant when it was a Cry1Ab corn plant is approximately 30% to 65%. The range for third instars moving off of an infested plant when it was a Cry1F corn plant was approximately 20% to 60%, and that the range for third instars moving off of an infested plant when it was a non-lepidopteran protein marked refuge corn plant was about 6% to 18%. The range of movement off of the infested plant for the protein marked refuge plants was consistent with that for near isoline control plants. The lepidopteran targeted Bt Cry proteins were found to be consistently detected for seven sampling points over a 24 hour feeding period. However, the non-lepidopteran Bt Cry proteins could not be consistently detected over the same 24 hour period. Additionally, the persistence of Bt plant material in third instars varied depending on the Cry protein. Future research using ELISA plate methods could yield more consistent results for the non-lepidopteran Bt Cry proteins.