Field and store ecology of the larger grain borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) in Kenya

The ecology of Prostephanus truncatus (Horn) in the field and store was investigated under the Kenyan climatic conditions and farming systems. In a field survey, no pre-harvest infestation in the farmers' maize fields was detected. However, maize on a research farm 100m or more from known source of infestation, were infested with incidences less than 1%. A store with infested maize offering about 20,000 adult P. truncatus and only 5m from the maize in fields, increased the incidences of infestation to an average 23%. Maize cobs without husks caused more incidences of field infestation. It was estimated that adult P. truncatus flew a mean distance of 925m from take-off to first landing under natural conditions. Only adult males were found to attract other P. truncatus; more females were attracted than males, suggesting that the pheromone produced was basically a sex attractant. Distribution of the pest in an experimental store was influenced initially by gravitational forces and later by the grain quality. Sitophilus zeamais (Mostch.) was numerically dominant to P. truncatus at all stages of storage. The introduced predator, Teretriosoma nigrescens Lewis was particularly effective against P. truncatus in stores that were insect-proofed by a wire-gauze. The population of some indigenous hymenoptera (especially Holipyris sylivanidis) trapped above experimental stores, seemed to fluctuate in a similar manner as P. truncatus, suggesting a numerical dependence of one on another. In conclusion, it is suggested that the introduced predator may have a role in pest management, but more investigations over more seasons are needed before its effectiveness can be fully evaluated.