Corn Earworm, Helicoverpa zea (Lepidoptera: Noctuidae) and Other Insect Associated Resistance in the Maize Inbred Tex6

A 2-yr field and laboratory study investigated insect resistance of the maize, Zea mays L., inbred Tex6, which has previously demonstrated resistance to Aspergillus ear rot and aflatoxin production, relative to susceptible inbred B73. Field studies indicated significantly greater resistance to insect feeding of V4-V8 growth stage Tex6 plants compared with B73 plants in both years, primarily to flea beetles (Chaetonema spp.). Field studies of natural (1999) and artificial (2000) infestations of corn earworms, Helicoverpa zea (Boddie), indicated much lower levels of kernel damage at milk stage (approximately three-fold) and smaller surviving larvae (approximately three-fold) in Tex6 compared with B73 ears. At harvest similar trends in reduction of numbers of damaged kernels per ear, as well as incidence and numbers of kernels per ear symptomatically infected by Fusarium spp. were noted. Laboratory studies indicated little difference in mortality or survivor weight of caterpillars or sap beetle adults caged with milk stage kernels of the two inbreds. However, assays with silks indicated significantly greater mortality of H. zea in both 1999 and 2000, and European corn borer, Ostrinia nubilalis (Hubner) in 1999 (only year tested) when fed Tex6 silks compared with B73 silks. Pollinated Tex6 silks were generally darker colored and more toxic than unpollinated silks. Thus, it is possible that commercially usable inbreds with resistance to insects, which also contribute to the mycotoxin problem through vectoring and damage, could be produced using Tex6 as a source.