Differential Response of Two Agroecosystem Predators, Pterostichus Melanarius (Coleoptera : Carabidae) and Coccinella Septempunctata (Coleoptera : Coccinellidae), to Habitat-Composition and Fragmentation-Scale Manipulations

Using alternating patches of weeds and crop [broccoli, Brassica oleracea (L.) (Brassicaceae)], vegetation composition and the spatial scale at which the vegetation was fragmented were manipulated in a factorial design field experiment. The effects of these manipulations were different for two common agroecosystem predators sampled. Sevenspotted lady beetles, Coccinella septempunctata (L.), were unaffected by vegetation-composition treatments but responded strongly to fragmentation-scale manipulations. The beetle Pterostichus melanarius (Illiger) was unaffected by both fragmentation-scale and vegetation-composition manipulations. These findings highlight the challenge of developing a predictive theory of the effects of vegetation diversification on assemblages of predators in agroecosystems.