Varietal resistance of stored maize to prostephanus truncatus (horn) (Coleoptera:Bostrichidae) and Sitophilus Zeamais (Motsch.) (Coleoptera: Curculionidae) in Tanzania.

The study objective was to investigate varietal resistance of some stored maize to the Larger Grain Borer (LGB), Prostephanus truncatus and the maize weevil, Sitophilus zeamais in laboratory and field conditions. The studied maize varieties were UCA, CH6, Kilima, Staha, CH3, Kito, TMVI, Katumani. The resistance of the varieties to the pests was measured by using the Index of Susceptibility (IS) which was significantly different ( P < 0.001, 7) among the varieties. Mean weight losses of the varieties were significantly different at P < 0.001. Weights of F adults of each species were the same. Electrophoresis indicated different levels of vitellogenin in haemolymph of the female insects reared on different varieties reflecting varying reproductive performance of the insect species on each variety. The weight losses of the varieties and vitellogenin levels from insects haemolymph exhibited the same trend with the IS of the varieties to the insects. Assessment of a combined effect when P. truncatus and S. zeamais were infesting the same varieties simultaneously exhited varying reproductive performance of the insects at F2. Hardness of the maize grains was negatively correlated with the IS of the variety, r = - 0.979 and - 0.067, P < 0.001 for P. truncatus and S. zeamais respectively. Starch contents of the grains were positively related to IS of both P. truncatus and S. zeamais, r = 0.999 and 0.995, P < 0.001 respectively. Grain hardness and starch content showed negative relationship. Protein and mineral contents of the varieties did not show any influence on the resistance of the varieties to the insects. Field experiments at Wami-Dakawa and Kipera sites revealed the same susceptibility trend of the varieties to the insects as the IS of the varieties in the laboratory. Katumani was the most resistant variety while UCA was the least of them all. It was concluded that P. truncatus was a more damaging insect pest of maize than S. zeamais and that the eight varieties had varying resistance to both pests. A search for more components for Integrated Pest Management (IPM) in grain storage ecosystems was recommended.