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The population dynamics of Prostephanus truncatus storage pest which was accidentally introduced into Togo, were observed in a study of farm-level maize storage. The damage and loss potential of the pest and its relationship with endemic pests and useful insects were also included. Further investigations were also made regarding the survival and reproduction of P. truncatus on endemic species of wood and other substrates.
The predator, T. nigrescens, was imported from the native home of the pest to control the Larger Grain Borer biologically. Initial investigations on the efficacy of the useful insect were carried out in a quarantine cage and in jars. In view of possible side-effects the predator could have, its behaviour on stored plant-based produce was examined. The investigations were concluded by releasing the imported predator in Togo.
1. The imported pest, P. truncatus was able to assert itself against competition from endemic pests and develop into, in some cases very large, populations. Infestation did not occur in all stores. Evidence of the pest being present throughout the year was provided with the aid of pheromone traps.
2 The useful endemic fauna evidently did not restrict the Larger Grain Borer in any way. A. calandrae and X. flavipes were able to suppress growth of the pest population in jar experiments, but in the natural environment these two species of useful insects had no or very little effect.
3. In the case of gradation of the population of P. truncatus very great damage and dry-weight losses occurred. Infested cobs were frequently destroyed completely which greatly affected the structure of damage. The damage and losses exceeded the level reached in stores without infestation by this pest.
4. P. truncatus is able to survive on the types of wood normally used for building stores for a period of at least 3 months. The female pests are still able to reproduce after this period. The upper level for survival seems to be around 4 months under conditions predominant in Togo.
5. P. truncatus was able to reproduce on wood of the species M. esculenta and P. regia. It was able to multiply on S. tragacantha.
6. Under near-to-practical conditions in a quarantine cage, the predator introduced, T. nigrescens, was able to significantly affect the population of P. truncatus .After an experimental period of 9 months 80% fewer adult P. truncatus were recorded in the presence of the predator. The damage and loss values were reduced by 41.6% and 46.5%.
7. The predator T. nigrescens evidently had no trouble in adapting to the predominant climatic conditions. The population of the predator grew substantially not only under near-to-practical conditions but also in jar experiments.
8. The predator T. nigrescens was not attracted clearly to the various stored products. Only a comparatively low number of adult T. nigrescens were found on the stored products openly offered to T. nigrescens in the quarantine cage. When T. nigrescens was artificial introduced to the stored products, the beetles left the jars within a short time.