Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 23, 1998
Publication Date: N/A
Interpretive Summary: In recent years, there has been much interest in developing crop plants with genes that encode insecticidal proteins isolated from the bacterium Bacillus thuringiensis (Bt). These proteins have proved to be highly effective against some insects; however, their effectiveness varies with different insects, crops, and plant tissues. In previous work, we demonstrated that southwestern corn borer larvae that fed on leaf tissue of Bt corn hybrids were killed and that both survival and growth of fall armyworm were reduced. In this investigation, we found that when fed on laboratory diets containing Bt hybrids, both southwestern corn borer and corn earworm larvae were killed. Survival of fall armyworm larvae was reduced approximately 35%, and the surviving larvae weighed only about 10% as much as those fed on tissue of non-Bt hybrids. When fed on diets containing silks from Bt hybrids, southwestern corn borer larvae were killed and corn earworm and fall armyworm larvae were reduced in size. The adverse effects on larval growth of husks and silks from Bt corm hybrids in these bioassays indicate that ear damage resulting from insect feeding should be reduced. Less damage will result in greater yields and higher grain quality.
Technical Abstract: The development of crop plants expressing genes that encode insecticidal proteins isolated from the bacterium, Bacillus thurnigiensis (Bt), has provided a tremendous opportunity for improved control of insect pests. Corn, Zea mays L., germpasm with resistance in the whorl stage of growth to leaf feeding by fall armyworm, Spodoptera frugiperda (J.E. Smith), and southwestern corn borer, Diatraea grandiosella Dyar,has been identified and released. Little progress, however, has been made in identifying resistance to ear damage by these insects. Husks and silks were collected 3 to 4 d after anthesis from nontransgenic and transgenic corn hybrids and used in laboratory bioassays to determine the effects of the Bt insecticidal protein on larval survival and growth of fall armyworm, southwestern corn borer, and corn earworm, Helicoverpa zea (Boddie). Southwestern corn borer larvae that fed on diets containing husks or silks from transgenic plants did not survive. Corn earworm larvae fed on diets containing husks of transgenic plants died, and those that fed on diets containing silks harvested from transgenic plants exhibited reduced survival and growth. Fall armyworm larvae were least affected by the Bt protein, but survival and growth of larvae on diets containing husks of transgenic plants were reduced. Larval growth was also reduced on diets containing silks from transgenic plants. The bioassays indicated that expression in husks and silks of genes encoding Bt insecticidal proteins could be useful in reducing insect damage in ears of corn.