European corn borer (Lepidoptera: Pyralidae) feeding behavior and survival on transgenic corn containing CryIA(b) protein from Bacillus thuringiensis

The effect of short-term exposure of European corn borer (Ostrinia nubilalis (Hubner)) larvae to transgenic corn expressing cryIA(b) protein from Bacillus thuringiensis subsp. kurstaki (Btk) on leaf consumption and larval survival were compared to negative controls in laboratory bioassays. Neonates and fourth instars were allowed to feed for one of three time periods (1994 bioassays: 1, 4: or 24 hours; 1995 bioassays: 24, 48, or 72 hours) on leaf sections of either cryIA(b)-expressing or control leaf sections before being transferred to artificial diet. Field-grown plants of the transgenic corn lines MON802 and MON810 were used as the source of leaf material in 1994 and 1995, respectively (YieldGard(TM) genes, Monsanto). Leaf source and exposure time significantly affected consumption ratings of neonates with little feeding detected on cryIA(b) leaf material during the first 24 hours during 1994 or during the first 72 hours in 1995. In 1994, cryIA(b) content in leaves did not affect neonate survival at transfer (97%) or after 2 weeks on diet (87%). In contrast, only 35-40% of neonates were alive after 24 and 48 hour feeding periods and no larvae survived 72 hours in 1995. Of the live neonates transferred to diet, 53% and 26% died within 2 weeks for cryIA(b) and control leaves, respectively. For periods of 24 hours or more, at least 90% of the fourth instars initiated feeding, regardless of cryIA(b) content. Cumulative consumption ratings were 46-67% lower for larvae exposed to cryIA(b) expressing leaves; however, survival rates at transfer or after two weeks on diet were not affected by leaf source. Implications for resistance management are discussed.