Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 10, 1995
Publication Date: N/A
Interpretive Summary: The southwestern corn borer is a serious pest of corn throughout much of the southern United States. When plants are infested at or after anthesis, larvae feed initially on leaf sheaths and husks of developing ears for several days before boring into the stalks. Tunneling within the corn stalks causes substantial reductions in yield and increases stalk lodging. A laboratory bioassay was developed in which southwestern corn borer larval growth on freeze-dried husks of different corn lines was determined. Significant differences in larval growth were found among the lines evaluated. The bioassay should be helpful in selecting corn lines that will exhibit resistance to southwestern corn borer after anthesis in the field. These lines can then be used in developing corn hybrids with southwestern corn borer resistance that can be grown by corn farmers. Resistant corn hybrids will reduce the need for insecticides in corn production.
Technical Abstract: Southwestern corn borer, Diatraea grandiosella Dyar, is a serious pest of corn, Zea mays L., in the southern United States. Corn germplasm with resistance in the whorl stage of growth has been developed and released; however, germplasm with resistance after anthesis has not been identified. The lack of reliable techniques for evaluating germplasm for resistance to southwestern corn borer after anthesis has contributed to difficulties in identifying resistant germplasm. A laboratory bioassay was developed for evaluating southwestern corn borer larval growth on diets comprised primarily of lyophilized husks of corn inbred lines because husks are the initial source of food for southwestern corn borer larvae on postanthesis corn plants. Diets were prepared by adding 15 g of lyophilized husk tissue collected within 3 d after silk emergence to a mixture of 250 ml distilled water, 2400 mg agar, 12.5 mg gentamicin sulfate, 132 mg sorbic acid, and 528 mg ascorbic acid. Larvae were weighed after feeding on the test diet for 21 d. Larvae fed diets containing husks of different inbred lines varied significantly. Larvae fed on husk tissue of the inbred line T202 were consistently smallest and weighed only about 20% as much as the heaviest larvae. Larvae fed husks of Ab24E and SC343 were consistently among the heaviest. Because southwestern corn borer larvae that infest corn plants at or after anthesis feed initially on husks, this bioassay is a potentially useful technique for identifying corn germplasm with resistance to southwestern corn borer. It could be useful in selecting genotypes for field testing and as a supplement to field tests.