Insect phitophagous and predators incidence on maize and bean cultivated in exclusive and intercropped systems

Este trabalho foi conduzido em Coimbra, MG, no ano agrícola 1996/97 e objetivou avaliar a ocorrência de insetos fitófagos e de predadores no milho e no feijoeiro cultivados em sistema exclusivo e em policultivo. Foi realizado um cultivo de milho (25/10/1996 a 24/03/1997) e dois cultivos de feijão [o primeiro de 25/10/1996 a 20/01/1997 (cultivo "das águas") e o segundo de 25/03/1997 a 21/07/1997 (cultivo "da seca")]. Realizaram-se contagens diretas das populações de insetos fitófagos e de predadores nas culturas. Menores densidades populacionais de herbívoros considerados preferenciais da cultura do milho [Dalbulus maidis (Delong & Wolcott) (Homoptera: Cicadellidae) e Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae)] e do feijoeiro [Diabrotica speciosa (Germ.), Cerotoma arcuata (Oliv.) (Coleoptera: Chrysomelidae) e Empoasca kraemeri (Ross & Moore) (Homoptera: Cicadellidae)] estiveram associadas ao cultivo consorciado. As densidades de herbívoros generalistas como Thrips tabaci Lind. (Thysanoptera: Thripidae) e Pseudoplusia includens (Walk.) (Lepidoptera: Noctuidae) foram maiores no feijoeiro consorciado com o milho. No cultivo "das águas", o total de insetos fitófagos foi maior no feijoeiro consorciado com o milho do que no feijoeiro cultivado exclusivamente, sendo que o inverso ocorreu no cultivo "da seca". Os predadores Anthicus sp. (Coleoptera: Anthicidae) e Hymenoptera: Formicidae foram mais abundantes no milho e no feijoeiro cultivados exclusivamente do que as culturas foram consorciadas. _____________________________________________________________________________________ ABSTRACTThis work was carried out in Coimbra, MG,Brazil, during the agricultural year of 1996/97 and it had the objective of evaluating the phytophagous insects and predators occurrence in maize and bean cultivated in exclusive and policultive systems. One cultivation of maize (from 10/25/1996 to 03/24/1997) and two cultivation of bean were conducted [the first one from 10/25/1996 to 01/20/1997 (rainy period cultivation) and the second one from 03/25/1997 a 07/21/1997 (drought period cultivation)]. The population of phytophagous insects and predators incident in the cultures were counted directly. Lower herbivores population density, which attacks preferentially maize [Dalbulus maidis (Delong & Wolcott) (Homoptera: Cicadellidae) and Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae)] and bean [Diabrotica speciosa (Germ.), Cerotoma arcuata (Oliv.) (Coleoptera: Chrysomelidae) and Empoasca kraemeri (Ross & Moore) (Homoptera: Cicadellidae)] were associated to the intercropped system. The generalists-insect densities as Thrips tabaci Lind. (Thysanoptera: Thripidae) and Pseudoplusia includens (Walk.) (Lepidoptera: Noctuidae) were higher in the bean intercropped with maize. The phytophagous-insect total number was higher in the bean intercropped with maize in the rainy period cultivation than in the bean cultivated exclusively. The opposite happened in the drought period cultivation. The predators Anthicus sp. (Coleoptera: Anthicidae) and Hymenoptera: Formicidae were more abundant in the maize and bean cultivated exclusively than when the cultures were cultivated intercropped