|Shepard, Merle - CLEMSON UNIV. SC|
Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 2004
Publication Date: August 1, 2004
Citation: Farrar, R.R., Shapiro, M., Shepard, M. 2004. Activity of the nucleopolyhedrovirus of the fall armyworm (lepidoptera: nocuidae) on foliage of transgenic sweet corn expressing a cryia(b) toxin. Environmental Entomology 33:982-989. Interpretive Summary: Crop plants that have been genetically engineered to resist insect pests are becoming increasingly common. Corn plants that have toxins from the bacterium Bacillus thuringiensis (Bt) resist a variety of caterpillars, including the corn earworm and European corn borer. The fall armyworm is another major pest of corn throughout the warmer parts of the Americas. However, Bt corn plants are generally not very resistant to the fall armyworm. It does kill some fall armyworms, and stunts those that survive, but many survive and can do damage. Bt corn may thus still need additional treatments to control this pest. There is a natural virus that kills fall armyworm caterpillars. It is harmless to people, wildlife, and beneficial insects such as bees. We tested this virus in the laboratory to see if it might be useful as a supplemental control for the fall armyworm on Bt corn. We found that the virus does kill fall armyworms feeding on Bt corn, though not any better than it kills ones feeding on non-Bt corn. We believe that if Bt corn kills part of the fall armyworms feeding on it, adding the virus may kill enough of the remaining caterpillars to prevent significant damage. We expect this information to be used by other scientists developing better and safer ways to control the fall armyworm. We will also use the information as a basis for testing the virus in the field. This information will lead to improved insect control while also reducing insecticide use and the problems of environmental contamination and worker exposure.
Technical Abstract: The activity of the nucleopolyhedrovirus of the fall armyworm, Spodoptera frugiperda (J. E. Smith), (SfMNPV) on transgenic sweet corn, Zea mays (L.), expressing a CryIA(b) toxin from Bacillus thuringiensis (Berliner) was studied in the laboratory. As this Bt corn has only limited efficacy against the fall armyworm, SfMNPV was evaluated as a supplemental treatment. When fall armyworm larvae reared on transgenic or nontransgenic foliage were fed equal numbers of occlusion bodies (OB), measured as either OB per larva or OB/mg larval weight, mortality was higher for larvae feeding on transgenic corn. However, when larvae were allowed to feed ad libitum on treated foliage, mortality was higher on the nontransgenic corn. Rates of food consumption were higher on nontransgenic corn, resulting in ingestion of more OBs, apparently countering increased susceptibility of larvae on transgenic corn.