| The population dynamics of the southwestern corn borer (SWCB), Diatraea grandiosella Dyar (Lepidoptera: Pyralidae), and its associated natural enemies were studied in six commercial corn fields from 1984 to 1986 in the Texas High Plains. Life table analysis indicated mortality was greatest during the egg stage of the first generation SWCB; whereas, mortality of second generation SWCB was greatest during the large larval and diapausing larval stages. Mortality from natural enemies or from intraspecific competition was negligible during the first generation and was density-independent. Mortality of large larvae during the second generation occurred in a density-dependent manner. Cannabalism and infection by Beauveria bassiana (Balsoma) were identified as major causes of mortality during the large larva stage and were considered responsible for the observed density-dependent mortality.; Adult SWCB which developed on whorl stage corn as first generation larvae oviposited more (P = 0.05) eggs than second generation adults developing as larvae on post-tassel stage corn. Total generation survival and net reproductive rate (Ro) were much higher for first than second generation SWCB and were identified as important factors leading to observed widespread economic infestations of second generation SWCB.; Thirty foliage-dwelling and 12 ground-active predatory arthropods were identified from corn. The minute pirate bug, Orius insidiosus (Say), and spiders, particularly members of Linyphiidae, were important predators of SWCB based upon their season long abundance in the field, distribution on the corn plant, and laboratory feeding studies. Insect parasitism of SWCB larvae and pupae was absent, though Trichogramma spp. commonly parasitized SWCB eggs.; SWCB egg mortality in the field due to natural enemies was insignificant on whorl and tassel stage corn as shown by mechanical exclusion cage techniques. Larval SWCB densities were greater (P = 0.05) in one of two years when natural enemies were excluded in whorl stage corn. Early instar SWCB larval densities were greater (P = 0.05) in both years in tassel stage corn in the absence of natural enemies.; Apanteles diatraeae Muesebeck successfully parasitized SWCB larvae in whorl and tassel stage corn in field cages although parasitism levels were low. A. diatraeae was not recovered from diapausing SWCB. Results suggest A. diatraeae is not well adpated to overwintering as immature larvae within diapausing SWCB. |
