Ideally, the best pest control will be no pest control—if ARS researchers in Columbia, Missouri, succeed in transferring rootworm resistance from eastern gamagrass into adapted corn germplasm. This could later be used by private breeders to develop commercial hybrids.
In a project under way since 1991, ARS entomologists B. Dean Barry and Bruce E. Hibbard, plant breeder Larry L. Darrah, and plant geneticist Edward H. Coe have been evaluating gamagrass, Tripsacum dactyloides, and exotic maize from Mexico and Central America. The scientists are in the ARS Plant Genetics Research Unit located at the University of Missouri.
"We already knew that mature gamagrass plants had some resistance to rootworms," says Hibbard. "But to protect corn all the way from seedling stage through flowering, we needed to find rootworm resistance in gamagrass seedlings."
In greenhouse studies, former ARS entomologist Dan J. Mollenbeck, Hibbard, and Barry tested 50-day-old gamagrass and corn seedlings, which they infested with 50 western corn rootworm eggs.
Larvae feeding on the gamagrass seedlings weighed less than those feeding on the corn. In further studies, they found that only three larvae survived on a total of 20 gamagrass plants, while one larva per plant survived on the corn. These results established for the first time that gamagrass is resistant in the seedling stage, as well as in the mature stage.
More cropland is treated with insecticides for corn rootworms than for any other insect pest.
While about a third less insecticides are used on row crops than the amount of herbicides applied for weed control, this research is being done in an effort to reduce the overall use of agricultural chemicals and improve water quality in the Corn Belt.
Hibbard is also studying how corn rootworms behave while selecting their host plants. Studies are in progress to evaluate a more uniform hatching strain of rootworms, which will enhance plant-screening accuracy. — By Linda Cooke, ARS.