DIFFERENTIAL RESPONSE OF TWO AGROECOSYSTEM PREDATORS,PTEROSTICHUS MELANARIUS(COLEOPTERA: CARABIDAE) ANDCOCCINELLA SEPTEMPUNCTATA(COLEOPTERA: COCCINELLIDAE), TO HABITAT-COMPOSITION AND FRAGMENTATION-SCALE MANIPULATIONS

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Abstract
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 beetlePterostichus 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.