Developmental biology of Bean Leaf Beetle (Ootheca mutabilis) on common bean

Abstract

Common bean (Phaseolus vulgaris L.) is a major source of food and income for people in sub Saharan Africa. Attack by Bean Leaf Beetles (Ootheca spp. Chev.) is one of the major causes of yield loss to the crop, causing up to 48.9% grain yield loss. Despite the damage, there is limited information on the biology, including preferred oviposition sites and development, of Ootheca spp. This information provides strategic entry points to potential control interventions. The objective of this study was to investigate the oviposition and development duration of O. mutabilis, which is the most abundant and damaging species of Ootheca on common bean in Uganda. A screenhouse study was conducted during 2019, using the common bean variety, NABE 16. Parameters monitored included type of oviposition sites, egg cluster size, and morphological changes and development duration for each stage. The beetles preferred to lay clustered eggs than singly, and oviposited in crevices or cover surface, and near plant stalks or roots, which protects the eggs and ensuring the neonates easily find their food. Development of O. mutabilis took 120 days with the larval stage lasting the longest; followed by pupae and eggs at 75, 24 and 22 days, respectively. This long biological cycle of the beetle goes beyond that of most common bean varieties of the bush type, implying that juvenile stages of the beetles remain in the soil after bean harvest. As a management strategy, we recommend rotation with non-host crops such as maize in order to break the biological cycle of the beetles, and open tillage to expose the beetles in the soil to extreme weather and natural enemies. Further studies will be needed on the fertility, longevity and diapause mechanisms.