Suitability of sorghum grain for the development of the larger grain borer Prostephanus truncatus (horn) (Coleoptera: bostrichidae)

Abstract

Laboratory studies were carried out to determine the development of the Larger grain borer Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) on sorghum grain. Substrate suitability, susceptibility and preference tests were conducted. Tests were conducted using P. truncatus on 3 sorghum (2 high-yield [Framida and Naga-White] and 1 native [mankaraga]) and 1 maize (native) cultivars. The beetle successfully completed its life cycle on sorghum grain, when stored as whole grain or finely ground grain flour. However, the beetle failed to develop on sorghum grain, when stored as coarsely ground grain. Mean development period of the grain borer was 36 to 60 days and differed with substrate type and grain cultivar. Mean number of first generation (F1) adult beetles recovered ranged from 1.51 to 13.6 individuals. In a similar manner, the mean weight of beetles produced ranged from 1.70 to 3.02 mg. Furthermore, P. truncatus showed higher preference for the high-yield improved sorghum cultivars (Framida & Naga-White) than the native one (Mankaraga). These high-yield improved sorghum cultivars were also more susceptible to attack by the stem borer. These cultivars have relatively soft pericarp and endosperm texture which offered low resistance to the boring and tunneling activities of these beetles. This indicates that in the absence of its most preferred host (maize), P. truncatus can subsist on sorghum grain. Thus sorghum grain can serve as a reservoir for P. truncatus. These findings should be exploited when designing biological control programmes in sorghum growing regions of sub-Saharan Africa.

Keywords: Prostephanus truncatus, sorghum grain, substrate suitability, susceptibility index, grain preference, biological control