Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2000
Publication Date: 12/1/2000
Citation: DOWD, P.F. INDIRECT REDUCTION OF EAR MOLDS AND ASSOCIATED MYCOTOXINS IN BT CORN UNDER CONTROLLED AND OPEN FIELD CONDITIONS: UTILITY AND LIMITATIONS. JOURNAL OF ECONOMIC ENTOMOLOGY. 2000. v. 93(6). p. 1669-1679. Interpretive Summary: The presence of ear mold toxins in corn results in losses of hundreds of millions of dollars each year. The presence of insects in corn ears frequently increases the levels of these toxins. Small plot and field studies run under natural conditions indicated that commercial Bt corn hybrids which express high levels of the Bacillus thuringiensis (Bt) insecticidal protein in silks and ears can greatly reduce levels of the mold toxin fumonisin when the principal damaging insect present is the European corn borer. Greater variability in beneficial insect populations were seen between different nonBt hybrids tested than between corresponding Bt vs. nonBt hybrid pairs. Adoption of these Bt hybrids should reduce losses to growers, result in a healthier corn product overall for people and animals, and also increase acceptability of these hybrids to importers due to improved health benefits.
Technical Abstract: In 1995, Bt ears of an experimental corn inbred artificially infested with European corn borer larvae were free from damage, while 40-50% on the corresponding nonBt ears had damage. Inoculated Bt ears were free of visible signs of Aspergillus flavus and Fusarium proliferatum, as compared to 30-40% of nonBt ears that had mold symptoms. Results in 1996 with the same inbred but half the Bt dose showed similar trends, and fumonisin levels were 3-fold lower in the Bt ears. In paired hybrid studies run in 1-acre fields from 1996-1998, a commercial Bt hybrid that expressed low levels of the Bt toxin in the silks and kernels typically had lower levels of insect damage and signs of Fusarium mold, but not fumonisin, compared to a corresponding nonBt hybrid. However, two Bt hybrids that expressed the Bt protein at high levels in silks and kernels examined in similar fields at the same site had much lower insect damage, mold, and fumonisin in both 1997 (30-40 fold less fumonisin) and 1998 compared to corresponding nonBt hybrids. In 1998, relatively high levels of corn earworms in the Bt hybrids and low populations of European corn borers were apparently responsible for lower differences in fumonisin levels between corresponding Bt and nonBt hybrids than in 1997, as fumonisin levels were still highly correlated with insect damage.