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ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Publications at this Location » Publication #140376
Title: LARVAL DISTRIBUTION AND SURVIVAL OF SECOND GENERATION EUROPEAN CORN BORER, OSTRINIA NUBILALIS (HUBNER) (LEPIDOPTERA: CRAMBIDAE) ON EVENT 176 BT CORN

Author
item ZOERB, AMELIA - UNIV. OF NEBRASKA
item SPENCER, TERENCE - UNIV. OF NEBRASKA
item Hellmich Ii, Richard
item WRIGHT, ROBERT - UNIV. OF NEBRASKA
item SIEGFRIED, BLAIR - UNIV. OF NEBRASKA

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2002
Publication Date: 1/15/2003
Citation: ZOERB, A.C., SPENCER, T., HELLMICH II, R.L., WRIGHT, R.J., SIEGFRIED, B.D. LARVAL DISTRIBUTION AND SURVIVAL OF SECOND GENERATION EUROPEAN CORN BORER, OSTRINIA NUBILALIS (HUBNER) (LEPIDOPTERA: CRAMBIDAE) ON EVENT 176 BT CORN. CROP SCIENCE. 2003. V. 22. P. 179-184.

Interpretive Summary: Several types of genetically-engineered (transgenic) plants have been produced that kill insects when they feed on crops. These plants offer an effective way to kill pest insects without conventional chemical insecticides, which translates into less surface and ground water contamination. Dramatic control of insects on these plants, however, has many scientists concerned about insects becoming resistant to these plants. Scientists have developed a high-dose refuge strategy to combat insect resistance, but there is evidence that not all types of Bacillus thuringiensis (Bt) corn produce a high dose of Bt. This study focused on European corn borer larvae that have completed development on Event 176 Bt corn hybrids. These larvae either survived exposure to sublethal doses of Cry1Ab Bt toxin or exploited plant tissues that do not express the toxin. To evaluate the impact of such exposure on larval establishment and survival, Event 176 plants with and without tassels and a non-Bt isoline were infested with European corn borer egg masses during pollen shed. On the non-Bt plants, larval establishment occurred primarily on pollen collecting in the leaf axils, silks and ears. In contrast, almost no larvae were recovered from leaf axils of the Bt treatments and at least 50% fewer larvae were recovered from the silks and ears during the first two weeks after infestation relative to the non-Bt plants. The larvae recovered from Bt treatments weighed significantly less than those observed in the non-Bt isoline at 4 weeks after infestation. By the eighth week, the larval weights of all three treatments were similar in three of four different field tests, suggesting that second generation larvae have the ability to compensate for initial exposure to sublethal doses of Bt toxin. These results suggest that second generation larvae completing development on Event 176 corn do not completely avoid exposure to the Bt toxin, although those that do survive are able to compensate for these sublethal effects. The implication of these results is that Event 176 hybrids do not appear to satisfy requirements for high dose that are recommended for resistance management purposes. These results provide important information to scientists and policy makers who are concerned with managing pest resistance to transgenic crops. Prolonging the value of these crops will benefit companies that produce these plants, producers, and consumers.

Technical Abstract: European corn borer (Ostrinia nubilalis) larvae that have completed development on Event 176 Bt corn hybids have either survived exposure to sublethal doses of Cry1Ab Bt toxin or exploited plant tissues that do not express the toxin. To evaluate the impact of such exposure on larval establishment and survival, Event 176 plants with and without tassels and a non-Bt isoline were infested with O. nubilalis egg masses during anthesis. On the non-Bt plants, larval establishment occurred primarily on pollen collecting in the leaf axils, silks and ears. In contrast, almost no larvae were recovered from leaf axils of the Bt treatments and at least 50% fewer larvae were recovered from the silks and ears during the first two weeks after infestation relative to the non-Bt plants. The larvae recovered from Bt treatments weighed significantly less than those observed in the non-Bt isoline at 4 weeks after infestation. By the eighth week, the larval weights of all three treatments were similar in three of four different field tests, suggesting that second generation larvae have the ability to compensate for initial exposure to sublethal doses of Bt toxin. In laboratory assays involving exposure of neonate larvae to silks of Event 176 and non-Bt corn, survival of neonate O. nubilalis was not different although larval weights were significantly reduced (2 to 6-fold). These results suggest that second generation larvae completing development on Event 176 corn do not completely avoid exposure to the Bt toxin, although those that do survive are able to compensate for these sublethal effects. The implication of these results is that Event 176 hybrids do not appear to satisfy requirements for high dose that are recommended for resistance management purposes.