Daniel M. Pavuk

GROUND BEETLE (COLEOPTERA : CARABIDAE) ACTIVITY DENSITY AND COMMUNITY COMPOSITION IN VEGETATIONALLY DIVERSE CORN AGROECOSYSTEMS

-Influences of weeds on activity density (number captured per trap per day), species richness and diversity of carabids (Coleoptera: Carabidae) in reduced tillage corn (Zea mays L.) plantings were examined in a 2-yr field study. Four treatments were examined: corn monoculture, corn with broadleaved weeds, corn with grassy weeds, and corn with a mixture of broadleaved and grassy weeds. Carabids were sampled with pitfall traps every 34 wk from May to September in 1988 and 1989. Neither broadleafed nor grassy weeds significantly influenced carabid activity density in 1988, a year of severe drought. However, in 1989, a year of normal rainfall, activity density was significantly greater in broadleaved weed treatments. Activity density of each of the major carabid species was affected differently by the treatments. Weedy vegetation in corn plantings generally did not have significant effects on carabid species richness, and community similarity was generally high for all treatments. Weeds had a significant negative effect on corn yields; the possible beneficial effects of such vegetation on enhancement of carabid activity density should be compared to the potential negative effect of corn yield loss. These results suggest carabid species respond differently to vegetational diversity, perhaps due to a number of factors, including suitable prey availability and microclimate preferences.

Influence of weed communities in corn plantings on parasitism of Ostrinia nubilalis (Lepidoptera: Pyralidae) by Eriborus terebrans (Hymenoptera: Ichneumonidae)

Abstract Parasitism of second generation European corn borer, Ostrinia nubilalis (Hubner), larvae by parasitoids was examined in corn (Zea mays) plantings having different weed communities. Treatments were corn without weeds, corn principally with broadleaf weeds, corn principally with grassy weeds, and corn with a mixture of broadleaves and grasses. O. nubilalis larvae were collected and maintained on artificial diet under constant environmental conditions in the laboratory to determine levels of parasitization. The ichneumonid, Eriborus terebrans (Gravenhorst), was the only parasitoid species reared, with the exception of a single tachinid, tentatively identified as Lydella thompsoni. Neither broadleaf nor grassy weeds had significant influences on parasitization of larvae during the study. Parasitism was positively correlated with host density (number of larvae per plant) in the corn-broadleaf weed community in 1988. Parasitism was greater in all treatments in 1989 than in 1988, ranging from 2.1 to 5.6% in 1988 and from 20.0 to 29.1% in 1989. The results were inconclusive as to whether weeds within corn plantings augment parasitism of O. nubilalis larvae by E. terebrans or by other parasitoids.

Influence of weeds within Zea mays crop plantings on populations of adult Diabrotica barberi and Diabrotica virgifera virgifera

The influence of weeds in corn plantings on abundance of adult Diabrotica barberi Smith & Lawrence and Diabrotica virgifera virgifera Le Conte (Coleoptera: Chrysomelidae) was examined. Four treatments were established: corn without weeds, corn principally with broadleaf weeds, corn principally with grassy weeds, and corn with a mixture of broadleaf and grassy weeds. Significantly greater numbers of D. barberi adults were collected from corn in treatments with broadleaf weeds than from corn in treatments without broadleaf weeds for both years of the study. Relative abundance of adult D. barberi on corn was not significantly different between treatments containing grassy weeds and treatments without grasses either year. Neither broadleaf nor grassy weeds significantly affected adult populations of D. virgifera virgifera either season; however, significantly more western corn rootworm beetles were collected from mixed weeds than from broadleaf or grassy weeds in 1989. The presence of broadleaf weeds in corn plantings could result in greater numbers of D. barberi adults on corn plants, and possibly greater oviposition.

Relationship between weed communities in corn and infestation and damage by the stalk borer (Lepidoptera: Noctuidae)

During 1988 and 1989, the relationship between different weed communities in corn plantings and infestation of and damage to corn by the stalk borer, Papaipema nebris (Guenee) (Lepidoptera: Noctuid...