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 t he vegetation was fragmented were manipulated in a factorial design field e xperiment. The effects of these manipulations were different for two common agroecosystem predators sampled. Sevenspotted lady beetles, Coccinella sep tempunctata (L.), were unaffected by vegetation-composition treatments but responded strongly to fragmentation-scale manipulations. The beetle Pterost ichus melanarius (Illiger) was unaffected by both fragmentation-scale and v egetation-composition manipulations. These findings highlight the challenge of developing a predictive theory of the effects of vegetation diversifica tion on assemblages of predators in agroecosystems.