Relative abundance and distribution of insect pests, ants and other components of the cocoa ecosystem in Papua New Guinea.
Abstract
Cacao has been grown on a large scale round Popondetta in the Northern District of Papua New Guinea since 1958. Pest problems were present in the area before that time, but, while most of the pests continue to be damaging, the Mirid Pseudodoniella laensis Miller is no longer important. A programme of eight, stratified, random pyrethrum knockdown samples taken every two weeks between December 1971 and January 1973 showed that the weevil Pantorhytes szentivanyi Mshl. was the most abundant pest present. It is also the most important because the larvae cause permanent damage and sometimes kill the trees by boring into the trunk, jorquette and branches. The pod and shoot damaging bugs Helopeltis clavifer (Wlk.) and Amblypelta theobromae Brown were less abundant, but sufficiently so to cause economic loss. Larvae of the moth Tiracola plagiata (Wlk.) were more abundant than A. theobromae, but it was concluded that many of the specimens taken had been feeding on the shade tree Leucaena leucocephala and not on cacao. Control of P. szentivanyi was evidently the first priority. Analysis of the relative distributions of pests, ants and other components of the cacao ecosystem confirmed earlier work showing that the ant Anoplolepis longipes (Jerd.) controls P. szentivanyi. A group of four cacao flush-feeding moth larvae (T. plagiata, Achaea janata (L.), Hyposidra talaca (Wlk.) and Ectropis sabulosa Warr.) was found to be associated with the use of L. leucocephala as a shade tree, as was damage by the bugs Helopeltis clavifer and Amblypelta theobromae. Implications of the study for cacao growing in the Popondetta area are discussed, and suggestions are made for future research, including the use of Anoplolepis longipes and coconut shade to minimize populations of P. szentivanyi.