Impacto e fatores determinantes de pragas em Phaseolus vulgaris

Abstract

Os objetivos deste trabalho foram determinar os componentes críticos e os fatores chave de perdas na cultura do feijoeiro (Phaseolus vulgaris) e identificar os fatores que determinam o ataque de pragas a esta cultura. Para tanto, foram realizados cultivos de feijão nas épocas de primavera-verão, verão-outono e inverno- primavera em plantio direto e convencional nos anos agrícolas de 2005/2006 e 2006/2007 em Coimbra, MG. Durante os cultivos monitoraram-se as perdas nos componentes de produção do feijoeiro e as densidades de insetos praga, de inimigos naturais e de artrópodes detritívoros. Os componentes críticos de perdas foram as flores, vagens e óvulos. Os fatores chave de perdas foram o abortamento de flores e a má formação de vagens e óvulos. As perdas por abortamento de flores estiveram associadas ao ataque de Bemisia tabaci, Caliothrips phaseoli, Empoasca kraemeri e Frankliniella occidentalis. As perdas por má formação das vagens estiveram v ii associadas ao ataque B. tabaci, Cerotoma arcuatus e Diabrotica speciosa. Já as perdas por má formação de óvulos estiveram associadas ao ataque de Thrips tabaci. Os fatores determinantes do ataque de insetos praga ao feijoeiro foram as épocas de cultivo, sistemas de plantio, os elementos climáticos, o estádio fenológico das plantas e os inimigos naturais. Os elementos climáticos que influenciaram a intensidade de ataque de insetos praga ao feijoeiro foram as chuvas, a temperatura do ar e o fotoperíodo. Os inimigos naturais, cujas densidades estiveram associadas a intensidade de ataque de insetos praga ao feijoeiro, foram o parasitóide Encarsia sp., os predadores aranhas, Calosoma sp., formigas, Geocoris sp., Nabis sp. e Orius incidiosus. Os insetos detritívoros Collembolla influenciaram positivamente as populações de aranhas, formigas e Calosoma sp.The aim of this work were to determine the critical yield components and key factors of yield losses on common bean (Phaseolus vulgaris) and identify the factors that determine pest attack in this culture. The bean crops was cultivated in three growing seasons, the spring-summer, summer-autumn and winter-spring arranged in two planting system, no-tillage and conventional. The experiment was carried out at the experimental field of UFV located in Coimbra, MG over 2005/2006 and 2006/2007. Losses in yield components and densities of insect pests, natural enemies and detritivores were monitored during experimental period. The critical components of losses were flowers, pods and ovules. The key factors was incomplete formation of pods, flower and ovule abortion. The flower abortion was associated with the pest attacks of Bemisia tabaci, Caliothrips phaseoli, Empoasca kraemeri and Frankliniella occidentalis. The incomplete formation of pods was correlated with the pest densities of B. tabaci, Cerotoma arcuatus and Diabrotica speciosa. The period of highest attack of Thrips tabaci was associated with ovule abortion. The growing seasons, planting system, climatic elements, developmental stage of plants and natural enemies were determinants factors of pest attacks. The climatic elements rainfall, temperature and photoperiod influenced the seasonality and pests densities. The natural enemies, whose densities were associated with the densities of pests were Encarsia sp., spiders, Calosoma sp., Ants, Nabis sp. and Orius incidiosus. Collembolla positively influenced the populations of spiders, ants and Calosoma sp.