Maize and cassava are two of the most important staple crops for people living in sub-Saharan Africa. For many of these people any change in the quantity of these two crops available to them can represent the difference between a good year and a lean year. It is therefore of paramount importance that any quantities of these crops harvested should be stored in as secure a manner as possible in order to minimise post harvest losses. In terms of current and, more especially, potential human impact the arrival of the Larger Grain Borer (Prostephanus truncatus) in Africa can best be described as a disaster.
Since its first reported sightings in East Africa (1981) and West Africa (1984) the insect has progressively extended its range such that it has now been found, and positively identified, in Benin, Burundi, Ghana, Guinea, Kenya, Tanzania and Togo. The degree to which the insect has impinged on the lives of the farmers and on the general economy of the country varies considerably but in some instances has been considerable. With some countries now refusing or being reluctant to accept maize from known LGB areas, the problem takes on a macro dimension for those affected countries that depend to some extent on exports to bring in foreign exchange.
Researchers based in many countries and in numerous institutes have addressed themselves to the problem of how best to combat this introduced pest in the most economic and effective manner. In East Africa the insect can be contained using a binary insecticide but this is not effective in stored cassava and nor does it control any insects present outside of the storage system in the general environment.
LGB is a bostrychid and as such a member of a family of typically wood boring insects. There is some evidence from its native area in the Neotropics that LGB may likewise be primarily a wood borer and only secondarily a pest of maize and cassava. If this is indeed the case it has grave implications for any control campaign aiming to control the insect that concentrates solely on the storage system.
In a situation such as this, with an introduced pest that occurs widely in the environment, it was widely felt that classical biological control could offer the potential for cheap, effective and long term control of the pest. A predatory histerid, Teretriosoma nigrescens was already known to be a predator of LGB in Central America and despite further searches for alternative control agents it was this beetle that seemed to offer the most promise.
Togo had expressed interest in the idea of releasing a biological control agent against LGB and once all preliminary safety tests had been done a coordination meeting was held to discuss results. The meeting, held under the auspices of IITA / FAO, was convened in Cotonou, Benin on the 2-3 June 1989. The outcome of the meeting was that it was felt that more research work should be done on T. nigrescens before it could be released in Togo. Specific further work was recommended and a follow up meeting was agreed upon at which, in the light of the work done, a final decision would be taken on whether or not to release T. nigrescens into Africa. These proceedings are a report of that meeting held in Lomé, Togo on the 56 November 1990.
As at the first meeting in Cotonou participants were invited from all the concerned countries and a number of interested organisations involved in LGB / biological control programmes. Their remit was to recommend, on the strength of the results from all the research that had been undertaken, whether it was safe, or not, to release T. nigrescens as a beneficial into Africa. It was clear that this was not a decision simply for Togo, as the likely first recipient of the agent, to make insects knowing no political boundaries or borders, some consensus of the delegates was required in order to formulate the recommendation.
The meeting, in terms of fulfilling its objectives, can be judged a success. A great deal of interesting new information was presented followed by sometimes spirited discussion. It was the editors task to try and summarise the essentials of these discussions and although we have done our utmost to make the report a fair and balanced summary of what took place we bear full responsibility for any omissions or misinterpretations recorded within. In order that the proceedings should become generally available as quickly as possible all the presentations are printed in the language in which they were given. For the same reason the format of the presentations has been altered as little as possible. Contributions that have been published elsewhere are given as abstracts. The recommendations of the various working groups of the workshop are presented here in both English and French.
We hope that participants and other readers will find this a useful addition to the stock of information already available for LGB and that the information herein will provide in some part the basis for a long term control method for the Larger Grain Borer in Africa.
M. Wright, NRI
J. Boeye, GTZ
Editors
Lomé-Togo
November, 1991