Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/15/2007
Publication Date: 12/1/2007
Citation: Nuessly, G.S., Scully, B.T., Hentz, M.G., Beiriger, R., Snook, M.E., Widstrom, N.W. 2007. Resistance to Spodoptera frugiperda (Lepidoptera: Noctuidae) and Euxesta stigmatias (Diptera: Ulidiidae) in sweet corn derived from exogenous and endogenous genetic systems. J. Econ. Entomology. 100(6):1887-1895. Interpretive Summary: Insects that feed on roots, foliage and reproductive organs such as the developing corn ears plague sweet corn production throughout the southeastern U.S. Two of the most damaging insects are the fall armyworm, which feeds on all plant tissues and the corn silk fly, which primarily feeds on emerging silk and developing corn kernels. Resistance to the feeding of the fall armyworm on the developing ears comes from various sources, but the two main sources include the “Bt” genes and a compound known as maysin. Resistance based on the Bt-11 gene, which was deployed into corn from the bacterium Bacillus thuringensis, produces a gut toxin that kills many caterpillar species. Resistance based on the maysin is produced naturally in the silk of the corn plant and is related to the flavanoid compounds typically produced by many plants. Resistance to the corn silk fly is unknown in sweet corn. The purpose of this research was to establish the efficacy of maysin as a natural deterrent to the corn silk fly in sweet corn and to compare this form of resistance to the established Bt-11 gene. This type of information is more important in sweet corn than field corn because the sweet corn industry has essentially a “zero-tolerance’ for insect damage on ears destined for fresh market consumption. Both insects caused less damage to the ears of two exotic varieties known as ‘Zapalote Chico 2451’ and Zapalote Chico sh2, which produce adequate quantities of maysin. The shrunken 2 (sh2) sweet corn hybrid ‘GSS 0966’, which has the Bt-11 gene exhibited resistance to the fall armyworm but not the corn silk fly. These results are the first to indicate that maysin confers resistance to both the fall armyworm and the corn silk fly.
Technical Abstract: Trials using Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) and Euxesta stigmatias Loew (Diptera: Otitidae) were conducted to evaluate resistance and potential damage interactions between the two species against Lepidoptera-resistant corn varieties derived from both endogenous and exogenous sources. The endogenous source of resistance was maysin, a C-glycosyl flavone. The Bt11 gene that expresses CryIA(b) insecticidal protein was the exogenous resistance source. Single species tests determined that varieties with either high maysin concentration (‘Zapalote Chico 2451’ and ‘Zapalote Chico sh2’) or CryIA(b) (GSS0966) were effective at reducing S. frugiperda larval damage compared to a susceptible check (‘Primetime’). Damage by E. stigmatias larvae was significantly lower in the two high maysin varieties than in either GSS0966 or Primetime in single species tests and when S. frugiperda were excluded from the ears.