Submitted to: Environmental Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/29/2010
Publication Date: 12/1/2010
Citation: Lundgren, J.G., Fergen, J.K. 2010. The effects of a winter cover crop on Diabrotica Virgifera (Coleoptera: Chrysomelidae) populations and beneficial arthropod communities in no-till maize. Environmental Entomology. 39(6):1816-1828. Interpretive Summary: Western corn rootworm is one of the worst pests of corn in the world, and although it is consumed by a variety of predators, its populations still outbreak to cause economic damage. Here, we tested whether a winter cover crop (slender wheatgrass, a native species of known agronomic benefit to corn production) might affect rootworm populations and damage either directly or by conserving rootworm predators. We found that rootworms developed at different rates in corn planted following a cover crop than those collected from corn grown under bare soil. Moreover, some larval stages were significantly smaller in the cover crop treatment. Finally, the oldest larvae were significantly less abundant in the cover cropped treatment. Predator populations were significantly greater in maize following the cover crop, especially as the season progressed. Finally, root damage was significantly reduced in the maize following cover crops in both years of study. The number of predators captured per plot was significantly and negatively correlated with the amount of root damage experienced. This data suggests that cover crops reduce rootworm performance and the damage they cause by having direct effects on the larvae and by encouraging rootworm predator populations.
Technical Abstract: The effects of an autumn-planted, spring-killed, grass cover crop (Elymus trachycaulus [Link] Gould ex Shinners) on populations of Diabrotica virgifera virgifera LeConte and its predator community were evaluated in South Dakota maize fields over two seasons. Abundance, size, and sex ratio of D. virgifera larvae and adults were measured in maize produced under two treatments (i.e., a winter cover crop or bare soil), as were maize root damage and the abundance and diversity of the predator communities collected on the soil surface and in the soil column. First and second instars and adults of D. virgifera were similarly abundant in the two treatments, but 3rd instars were significantly fewer in maize planted after a winter cover crop. Larvae developed at different rates in the two treatments, and 2nd instars were significantly smaller (head capsule width and body length) in the maize planted after a cover crop. First and third instars and adults were of similar size in the two treatments, and adult sex ratios were also similar. Although initially similar, predator populations increased steadily in the cover-cropped maize, which led to a significantly greater predator population by the time D. virgifera pupated. There was significantly less root damage in the cover-cropped maize. Predator communities were similarly diverse in both treatments. Predator abundance per plot was significantly and negatively correlated with the abundance of 3rd instars per plot. Clearly, winter cover crops reduce D. virgifera performance and their damage to the crop, and we suspect that this reduction is caused by both direct effects of the treatment on D. virgifera size and development, and of increased predation on the 3rd instars of the pest. Additional data on the impact of cover crops on actual predation levels, grain yield and quality, and farmer profitability, and correlations among pest performance, crop characteristics, and predator populations and behaviors are key components of this system that remain to be addressed.