Effect of common knotweed ( Polygonum aviculare ) on abundance and efficiency of insect predators of crop pests

Abstract

The entomophagous insects associated with common knotweed (Polygonum aviculare) were surveyed in California in 1980-84. Representatives of 36 insect taxa were observed feeding at the flowers; 29 of these groups containing entomphagous species. Other entomophagus insects were associated with Aphis avicularis. Among the predators frequently observed feeding at the flowers were species of Geocoris. Densities of Geocoris spp. were higher on common knotweed than on lucerne, prostrate pigweed (Amaranthus graecizans) or field bindweed (Convolvulus arvensis). Experiments were conducted to determine whether the association of entomophagous insects with common knotweed could be used to improve the biological control of insect pests on radishes, bell pepper (Capsicum annuum) and lucerne. From the results it was concluded that common knotweed, despite its attractiveness to numerous species of entomophagous insects, may have limited use in enhancing biological control on adjoining crops. The weed may provide alternative prey as well as floral resources, and thus represent such a hospitable habitat that some predators may have no tendency to forage on nearby crop plants. It is suggested, however, that pending further research, the weed should be tolerated at field edges as it may provide breeding sites and reservoirs from which predators might colonize agricultural fields.