Response of spiders (Araneae) to the introduction of an exotic pest (Diabrotica virgifera LeConte,1868 - Coleoptera, Chrysomelidae) in corn cultivations in northern Italy.
The response of spiders (Araneae) to the introduction of the corn rootworm (Diabrotica virgifera, Coleoptera Chrysomelidae, LeConte, 1868) was studied in 2010 and 2011 in two study areas in the Padana Plain (Northern Italy). The research was aimed at identifying the community of spiders which can prey on D. virgifera in corn fields, the rate of predation and the influence of landscape on the natural enemies' response to the invader. The two study areas were different in terms of both land use and agricultural patterns. In the area south of the Po River corn is cultivated together with many other crops, according to a crop rotation pattern, while in the area north of the Po River (Po) the agricultural landscape is mostly dedicated to rice monoculture. Predation was observed only in the area south of the Po River, ranging from 9.9% to 40.3%, where Phylloneta impressa (Araneae Theridiidae, Koch,1881) was the most important predator of corn rootworm adults. In the area north of the Po River no predation was recorded. Those results are one more example of how the richness and abundance of potential natural enemies can be crucially affected by structure and composition of the landscape surrounding crop fields. Predation by spiders could potentially support an integrated pest management of D. virgifera in agricultural districts where the pest is limited by crop rotation. The rate of predation was inversely dependent on victims' density, therefore predation by spiders tended to be of minor importance when D. virgifera was at epidemic levels.