SPIDERS (ARANEAE) AS PREDATORS OF THE EXOTIC Metcalfa pruinosa (SAY, 1830) (HOMOPTERA: FLATIDAE) IN THE CENTRAL WESTERN PO FLOODPLAIN (NORTHERN ITALY)

The planthopper Metcalfa pruinosa (Say, 1830) (Homoptera: Flatidae) was unintentionally introduced from North America to Europe and started its invasion from Italy in 1979. During 2004, a survey was carried out in a study area located in the central western Po floodplain (Northern Italy) in order to identify spiders feeding on M. pruinosa. Fourteen species of spiders preying upon the planthopper were recorded. The community of spiders mainly included species belonging to Agelenidae (27.4%), Linyphiidae (26.7%) and Araneidae (15.6%). Almost all remains of M. pruinosa found in the webs were adults of the pest, while the predation of juvenile stages was negligible. During summer 2005 and 2006, more specific observations were carried out, respectively, on Agelena labyrinthica and Linyphia triangularis that were identified in 2004 as the most common planthopper predators. M. pruinosa was regularly found in the webs of A. labyrinthica; predation rate was maximum in July and around the half of August, while it tended to decline during September. L.triangularis modulated its density in response to the increase of M. pruinosa density. M. pruinosa was recorded as the dominant prey in L. triangularis webs all summer long as far as the prey could be available.