Aspects of the Cocoa Weevil Borer Pantorbytes biplagiatus Guer in the British Solomon Islands Protectorate.

Abstract

Pantorhytes biplagiatus (Guer) is a serious pest of cocoa in the British Solomon Islands. In some farms it has caused the death of up to 50 per cent of trees three years old and older, and in a trial plot yields were reduced by 30 per cent over a four year period.
Insecticidal control is difficult and expensive. Control by hand removal of larvae and adults can be effective in small farms away from large infestations. This method is likely to prove tedious and expensive on larger plantations Two other possible methods of control are discussed. The first is the introduction of the ant Oecophylla smaragdina (F) to cocoa farms. Oecophylla is antagonistic to Pantorhytes. Lower numbers of larvae are to be found in trees on which Oecophylla is foraging. However, there are difficulties in introducing the ant into uncolonised young cocoa farms. These include competition from the ant Technomyrmex detorquens (Walk), enviromental factors, and possibly the availability of food. Further investigation of these factors is needed to determine the optimum timing for nest introductions. The second method is the use of less susceptible cocoa varieties. Amelonado and the progeny of clone Na32 were found to be less susceptible to Pantorhytes damage than Trinitario. These types have a thinner smoother bark than Trinitario and the number of egg laying sites for Pantorhytes is probably therefore reduced.