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1 Introduction and description of the problem
Teretriosoma nigrescens is a predatory beetle belonging to the family Histeridae. In Central America it is associated with Prostephanus truncatus (Coleoptera: Bostrichidae, wood borers), which attacks maize, as a host. The predator is evidently able to control the population of the pest to such a degree that P. truncatus does not cause any loss or damage worth mentioning in this region.
The larger grain borer (P. truncatus presumably spread to Africa by travelling in foodstuffs at the beginning of the eighties. Under favourable climatic conditions and without any natural enemies, it was able to develop in West and East Africa (Togo and Tanzania) in a short time into one of the most predominant storage pests, attacking stored maize cobs and dried cassava chips.
After promising initial investigations in the mid-eighties, a plan was compiled to introduce the natural antagonist of this pest, T. nigrescens, to Africa as a biological control agent for P. truncatus.
Although current findings show no evidence of arthropods, imported to combat pests which had spread, having negative effects on the ecological balance of the respective country, extensive investigations in Togo as the target country and under quarantine conditions in Germany were essential prior to release.
Consequently the focus of this work was to discover whether T. nigrescens makes use of other Coleoptera apart from the post-harvest pest P. truncatus as food or is able reproduce in their cultures. This was to provide the proof for the countries concerned that releasing T. nigrescens in Africa would cause no damage.
It would be a welcome fact if T. nigrescens also decimated other storage pests. However, if it appeared relatively unspecific, it could, e.g. turn into a threat to useful endemic insects.
To absolutely exclude that T. nigrescens itself is or would become a pest affecting stored produce, the significance of plant substrate for the nourishment and development of the hister beetle was investigated.
The following investigations are also to extend the biological and ecological data on T. nigrescens and to provide new scientific findings on predator-prey interaction.
This investigation, enhanced by the results of other scientists, should finally show that there is nothing to obstruct the implementation of a sensible and feasible method of controlling P. truncatus in a biological and integrated way. This is also to provide support for the urgently essential step of reducing the use of chemical pesticides in developing countries.
In January 1991, the predator T. nigrescens was introduced to Togo, and in May 1992, to Kenya, as a biological control agent for P. truncatus There are already initial results showing that the introduction of the useful insect in Togo has been successful. Other African countries, e.g. Benin and Malawi, are interested in introducing T. nigrescens.