Much of the research on agriculturally important insect herbivores and natural enemies has been conducted at the within-field scale. However, it is becoming increasingly clear that landscape-level habitats may be important in shaping insect communities and may differentially affect insect species depending on their trophic level and life history. In this study, we examined whether land-use patterns are correlated to the population densities of three herbivores (northern corn rootworm-Diabrotica barberi, western corn rootworm-Diabrotica virgifera, and European corn borer-Ostrinia nubilalis) and one generalist predator (pink-spotted lady beetle-Coleomegilla maculata) in corn fields (Zea mays). We hypothesized that herbivore populations would be highest in corn fields surrounded by simple landscapes that are dominated by agriculture, while a generalist predator would be most abundant in more heterogeneous landscapes that provide overwintering habitat and a diversity of prey. We tested this idea by surveying insects in upstate New York in 2006 and 2007 from corn fields that were surrounded by heterogeneous and more agriculturally dominated landscapes. Land-use patterns were quantified at multiple spatial scales ranging from field perimeters to 40km diameter regions around fields.
Results/Conclusions
None of the herbivorous insect populations were correlated to small scale land-use patterns. However, our results show that western corn rootworms respond to landscape composition at the 40 km scale and are significantly more abundant with increasing proportions of row crops in the landscape. Northern corn rootworms also showed a trend towards being more abundant in homogeneous landscapes while European corn borers showed no correlation with land-use at any scale. In contrast, pink-spotted lady beetle populations are significantly lower in simple landscapes dominated by agriculture and respond at smaller spatial scales ranging from the perimeter of fields up to 2km. These results indicate that regional land-use patterns can play important roles in the field-scale dynamics of agricultural insects, but that the effects vary by species. Furthermore, increasing habitat heterogeneity in agricultural landscapes may result in smaller herbivore populations while simultaneously supporting larger generalist predator populations.
