The role of ecological compensation areas on predator populations: an analysis on biodiversity and phenology of Coccinellidae (Coleoptera) on non-crop plants within hedgerows in Northern Italy

The role of natural vegetation, including trees, shrubs and weeds in supporting predatory insects with particular reference to Coccinellids, was investigated in a two-year field studies. The samplings were carried out by mechanical knock-down (MKD) and visual inspections (VIS) in hedgerow of Northern Italy (Bologna province) between March and October. Among trees and shrubs, Euonymus europaeus L. (spindle-tree) and Prunus spinosa L. (blackthorn) showed the highest number of predatory species, followed by Crataegus monogyna Jacques (hawthorn), Populus sp. (poplar), Cornus sanguinea L. (dogwood) L. and Corylus avellana L. (hazel). Salix alba L. (willow) and Pyrus pyraster Burgsdorf (wild pear) were characterised by the lowest level of predator diversity. Coccinellidae represented the most abundant family of insect predators on trees and weeds. Eggs and/or larvae of Coccinellidae were found in all the tree and shrub species sampled with the exception of Sambucus nigra L. (elder). Data demonstrate that some trees and shrubs species can provide shelter for adult ladybirds, mainly in late summer, when many crops in Northern Italy are harvested. A list of the Coccinellid species, including relative abundance on the most important plant species, is provided. The number of species sampled by MKD on hedgerows was higher than those sampled by VIS. Among the weeds, Cirsium sp., Rumex sp. and Urtica dioica L. (stinging nettle) supported the reproduction of Coccinellids. Only adults of Coccinellids were found on Daucus carota L., Amaranthus retroflexus L., Dipsacus sylvestris Hudson, Arctium sp., Crepis sp., Picris sp.. Correspondence analysis was used for the ordination of both plant and Coccinellid species and it was performed on the matrix of the data collected by VIS. The role of hedgerows and weeds in landscape management is discussed. Local biodiversity of beneficials in Bologna province can be conserved and improved by increasing “island” habitats like hedgerows and field margins.