Outbreak and Insecticide Susceptibility of Pod Feeding-larvae on Cocoa in Ghana

Abstract

Cocoa is an important foreign exchange earner and a major source of income for several households in Ghana. In 2018, a larval outbreak on cocoa pods was reported in Ghana. Although the origin is unknown, it was perceived to be a secondary pest outbreak. In this study, a survey was conducted in the outbreak areas to identify and determine the occurrence of the pest and its susceptibility to a commonly used insecticide. Field and laboratory studies were conducted to identify the pest, determine the level of infestation, insecticide susceptibility, and field management. The outbreak was mainly caused by larvae of Anomis leona (~96% infestation of cocoa trees in some communities) with extensive feeding damage (chewing channels/tunnels) on the pericarp of pods. Field populations of A. leona larvae from districts in the Central region subjected to bifenthrin were susceptible at the recommended field rate (0.0245%) for mirids after 48 h of exposure under laboratory conditions. The insecticide induced a median lethal concentration (LC50) of ≤0.0061% and ≤0.0018% on A. leona larvae from Jukwa and Twifo Praso in the Central region at 24 and 48 h of exposure, respectively. Field application of bifenthrin was able to suppress infestation. The findings show that Anomis larvae were responsible for the outbreak, inducing extensive damage on pods. Bifenthrin was toxic to the larvae and could be used to manage them on the field. The outbreak indicates the need to develop an integrated management and monitoring strategy for cocoa pests to minimize future outbreaks.