Bio-ecological studies of the mango stone weevil in southern Ghana.

Abstract

Field and laboratory studies were conducted to determine the distribution and biology of the mango stone weevil, Sternochetus mangiferae, in southern Ghana. The weevil was found in the coastal savanna and rain forest areas but appeared to be absent from the forest/savanna transition zones. All mango varieties were attacked within the infested zones, with higher rates of infestation in the more humid areas. Elsewhere, the weevil is reported to contribute substantially to premature fruit drop and causes reduction in yield. The eggs appear to be laid in young fruits over a period of time as some fruits recorded multiple infestations with all stages of development observable in a single fruit. In the laboratory both larvae and adults were reared on excised mango cotyledons, but it is doubtful that adults survive on cotyledons in the field. Larvae pupated for 6-7 days with a pre-pupal stage of 1-2 days. Adults are long lived and have been cultured in the laboratory for up to 6 months. Adults were found hibernating in cracks and crevices on trunks of old mango trees (> 20 years after planting). Similar hiding places could not be found on young trees (³ 10 years after planting). It is, thus, possible that trees other than mangoes provide hibernation sites for the weevil between fruiting seasons. Adult weevils readily accepted and climbed onto flowers but did not show any preference for bark, twigs, leaves or soil. The acceptance of the flowers by the adults seems to suggest that flowers may provide food and breeding sites. Infestation by the weevil did not affect fruit quality despite the high potential to disrupt the export trade in mangoes. The low quarantine rejection threshold of one fruit in 40 set in the export market suggests that solution to the problem posed by the weevil requires socioeconomic, political and scientific initiatives.