Biological studies of Gasteroclisus rhomboidalis (Coleoptera: curculionidae) on Amaranthus species

Abstract

In West Africa, the foliage of both wild and cultivated varieties of Amarnathus species is used widely as vegetable and as fodder for cattle. This widely cultivated vegetable is severely attacked by the snouted beetle, Gastreoclisus rhomboidalis. A comprehensive study on some aspects of the biology of G. rhomboidalis has been carried out. The full life cycle of the beetle (from copulation and oviposition through the various immature stages to the emergence of adult beetles) was investigated. It took on the average 40 days for the adult beetle to emerge from the day of oviposition. Studies on the feeding habit of the beetles revealed that the beetles fed heavily on the leaves and can inflict an enormous destruction on the host plant over a short period of time. Generally; the studies have been able to confirm that the larva and adult beetles are the most potent destroyers of the host plant. While the adult beetle fed heavily on the leaves and tender plant stem, the larva when hatched in the plant stem, destroyed the host plant (particularly during the tender ages of between 2 - 3  weeks) with its boring activities causing the plant to wilt and die.