Mortality of Helicoverpa zea (Lepidoptera: Noctuidae) Pupae in Ear-Stage Field Com

Abstract

The factors having an impact on the survival of the F2 seasonal generation of Helicoverpa zea (Boddie) pupae in southwestern Arkansas field corn were identified and quantified. Last instar (fifth or sixth instar) field-collected com earworm larvae (480 per yr) were allowed to pupate in fields under four treatments designed to provide three levels of natural enemy exclusion. Mortality of these pupae and samples of feral pupae were determined and mortality factors were identified. Recovery of exuviae and remains from placed pupae were excellent (94 and 96% in 1990 and 1991, respectively). Moths emerged from the vast majority of test pupae (82.3 and 93.9% in 1990 and 1991, respectively). The exclusion treatments had no effect on the incidence of mortality in either year. Mortality was higher in 1990 (11.7%) than in 1991 (1.9%) because of the collapse of emergence tunnels prior to or during moth emergence. The increased incidence of collapse may have been caused by a significantly lower clay content (7.03%) in 1990 than in 1991 (16.4%). Observed biotic mortality was extremely low (2.1% and <1% in 1990 and 1991, respectively) in spite of a rich predator fauna as identified from pitfall traps. The large number of earworm larvae surviving to pupation following larval development in the ear of field corn, combined with the observed low mortality rates, suggests that a large number of moths would emerge from each hectare of corn at a time when other crops, particularly cotton, are attractive for oviposition. Enhancement of pupal mortality in ear-stage corn by cultural or chemical means is impractical or impossible, thus providing support for implementation of a biological control program that targets H. zea pupae.