Simulated Soil Moisture and Planting Material Health on the Behaviour of Cosmopolites sordidus, Germar (Coleoptera: Curculionidae)

Abstract

The pest status of Cosmopolites sordidus has been related to farm sanitation, environmental conditions and local weevil biotypes. This study was to confirm the inherent fecundity of endemic weevils, soil moisture effect and planting material health status that may contribute to weevil behaviour. Adult banana weevils were confined to plantain rhizomes, which were then subjected to four soil moisture regimens for 65 days. In another experiment to measure potential fecundity, weevils collected from the farmer’s field were dissected to determine the internal egg follicles. Planting material with different initial weevil egg infestations on the pseudostem were confined below insect screening net in growing pots. Larva damage and stage populations were determined after 22 weeks. The results showed that weevils confined to plants under moisture stress had higher corm damage than irrigated and vigorously growing plants. A lower number of weevils were associated with plants under moisture stress than vigorously growing plants. The maximum number of mature egg follicles present in the ovaries of female weevils was 17. In general, the mean number of mature egg follicles was 4 per female adult weevil. Infested planting material with initial estimated number of 0.3 eggs per sucker resulted in 2.3 adult emergence and ≈ 34% corm cross section damage after 154 days. The potential egg follicles albeit slow weevil population build-up reiterates the k-selected nature of the banana weevil. The egg follicles in adult female ovaries were high and comparable with weevils in other banana growing regions. The default health status of planting material was confirmed to be a contributing factor to weevil build-up in confinement. Soil moisture increased weevil survival but the improved plant vigour compensated for weevil damage.