Biological control of the coffee berry borer (Hypothenemus hampei)
The coffee berry borer is an important world-wide pest which is difficult to control by spraying because much of its life cycle occurs deep inside the berry. Manual control (hand picking of berries) is laborious and expensive. Biological control is an obvious alternative, but even this is not an easy option because there are comparatively few known natural enemies of the borer. Two of these, the African bethylid wasps Cephalonomia stephanoderis and Prorops nasuta, have been extensively studied and released in a number of Latin American countries (Mexico, Guatemala, Honduras, El Salvador, Nicaragua, Colombia, Ecuador, Brazil) and at least one of them has established in all these places. However, available evidence suggests that their impact has been small, probably because the female of each species stays in one berry with her offspring, in a similar fashion to the borer itself. A third parasitoid, the eulophid Phymastichus coffea, has recently been introduced from Africa to Colombia. This is an unusual natural enemy in that it parasitises the adult female borer as she lies in the entry tunnel which she makes to the coffee endosperm. Unlike the bethylids, this wasp moves from berry to berry and hence may be more effective, and it also attacks the borer before it can damage the developing coffee bean. A model recently developed by Gutierrez in California also suggests that this wasp may be the most effective one and that a combination of P. coffea and C. stephanoderis may be especially good. Intensive efforts in Colombia and Mexico are being made to improve mass rearing methods using semi-artificial diet with the hope that one day it may be economically feasible to use mass releases to keep the borer under tight control.
There has also been much interest in the entomopathogenic fungus Beauveria bassiana, which is naturally present wherever the borer is encountered. The fungus can be cultured on rice grains in the laboratory, harvested, formulated and sprayed in a similar fashion to a chemical spray but with the advantage that it has very low toxicity to humans or other wild life. Recent work in Colombia suggests that concentrated spore solutions can kill a high percentage of borer, though this can take more than two weeks under field conditions and it is not a cheap alternative to chemicals. This, together with observed quality control problems in commercial production, means that much further research has to be done before it could be recommended for routine use by farmers.
Peter Baker
CABI Bioscience, Ascot, UK.
