MORTALITY OF HELICOVERPA-ZEA (LEPIDOPTERA, NOCTUIDAE) PUPAE IN EAR-STAGE FIELD CORN

The factors having an impact on the survival of the F2 seasonal genera tion of Helicoverpa zea (Boddie) pupae in southwestern Arkansas field com were identified and quantified. Last instar (fifth or sixth instar ) field-collected corn earworm larvae (480 per yr) were allowed to pup ate in fields under four treatments designed to provide three levels o f natural enemy exclusion. Mortality of these pupae and samples of fer al pupae were determined and mortality factors were identified. Recove ry 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 ex clusion treatments had no effect on the incidence of mortality in eith er year. Mortality was higher in 1990 (11.7%) than in 1991 (1.9%) beca use of the collapse of emergence tunnels prior to or during moth emerg ence. The increased incidence of collapse may have been caused by a si gnificantly lower clay content (7.03%) in 1990 than in 1991 (16.4%). O bserved biotic mortality was extremely low (2.1% and <1% in 1990 and 1 991, respectively) in spite of a rich predator fauna as identified fro m pitfall traps. The large number of earworm larvae surviving to pupat ion following larval development in the ear of field com, combined wit h the observed low mortality rates, suggests that a large number of mo ths would emerge from each hectare of corn at a time when other crops, particularly cotton, are attractive for oviposition. Enhancement of p upal mortality in ear-stage com by cultural or chemical means is impra ctical or impossible, thus providing support for implementation of a b iological control program that targets H. zea pupae.