The Effects of a Winter Cover Crop on Diabrotica virgifera (Coleoptera: Chrysomelidae) Populations and Beneficial Arthropod Communities in No-Till Maize

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 and size of D. virgifera larvae and adults and sex ratio of 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 third instars were significantly fewer in maize planted after a winter cover crop. Larvae developed at different rates in the two treatments, and second 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 third 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 environmental effects of the treatment on D. virgifera size and development, and of increased predation on the third 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.

Insect communities in soybeans of eastern South Dakota: The effects of vegetation management and pesticides on soybean aphids, bean leaf beetles, and their natural enemies

“…At least 17 species (representing five families) were collected in sweep samples, 65 taxa (representing 13 families) in pitfall samples, and 44 taxa (representing 17 families) in quadrat samples (Tables 1e3). Based on our density samples, we estimate that there are about 277,170 AE 30,283, 339,300 AE 84,100, and 594,800 AE 133,300 predators per ha on the soil surface in the chemical intensive, reduced chemical, and cover crop management systems, respectively. These numbers are within the range of previous estimates of natural enemies in cropland (Lundgren et al, 2006;Lundgren and Fergen, 2010).…”

“…However, when we examined actual densities of predators, carabid beetles were much less abundant than spiders, ants, and harvestmen in our systems (Table 3). These observations on actual densities of predators are supportive of other reports involving quadrat samples (Lundgren et al, 2006;Lundgren and Fergen, 2010). Regardless, employing multiple sample methods helps give a better understanding of predator diversity within soybeans of the Northern Great Plains.…”

“…Actual densities of surface-dwelling predators were monitored using quadrat samples (Lundgren et al, 2006;Lundgren and Fergen, 2010). A quadrat made of sheet metal (0.5 Â 0.5 m; 15 cm tall) was randomly placed within a plot for each sample observation, and the insects found within the top 1 cm of soil were aspirated.…”

“…Pests are often a symptom of producing crops under monoculture conditions, and efforts to increase the diversity of vegetation within cropland often increase natural enemy populations and reduce pest intensity (Andow, 1991;Tillman et al, 2004;Broad et al, 2009;Lundgren and Fergen, 2010;Letourneau et al, 2011;Lundgren and Fergen, 2011;Koch et al, 2012). Sources of this vegetation diversity may be in the form of low levels of weeds or the use of cover crops or ground covers.…”

Spiders from multiple functional guilds are exposed to Bt-endotoxins in transgenic corn fields via prey and pollen consumption

“…Within the predatory arthropods, spiders are common, abundant, and diverse in agroecosystems (Lundgren & Fergen, 2010;Lundgren et al, 2006;Nyffeler & Sunderland, 2003;Young & Edwards, 1990), including Bt crop fields (Duan et al, 2004;de la Poza et al, 2005;Sisterson et al, 2004). In addition to playing varied and essential roles in arthropod food webs (Wise, 1993), these generalist predators can be key predators of pests in crop fields (Greenstone, 1999;Harwood et al, 2004;Riechert & Lockley, 1984).…”