The response of maize varieties to damage by protephanus truncatus (horn) (coleptera: bostrichidae) in Tanzania

The Larger Grain Borer, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae} is a major pest of maize on farms in Tanzania. Experiments were conducted, using some commonly grown Tanzanian maize varieties, to determine their ability to resist damage caused by the feeding of P. truncatus. Damage was assessed by counting the number of Fl adults produced in similar infestations of different varieties of maize over the same period of time. The values produced were converted to indices of susceptibility of the maize varieties. Grain weight loss was also used as an indicator of varietal susceptibility to the pest. The experiments were maintained at between 27 and 30~0c and 60-80X Relative Humidity throughout the experimental period. Maize varieties studied included: Kilima; Staha; Kito; TMVI1;; Katumani and ICW. The physical, chemical and nutritional characteristics of the different maize varieties were also measured and compared to determine which of these factors were related to the differences in susceptibility, exhibited by the maize types tested. Laboratory studies showed that P. truncatus is a very damaging storage pest. Differences in the numbers of Fl adults produced were highly significant (P < 0.01) among maize varieties, giving significantly different indices of susceptibility (P < 0.01). Mean weight losses of the varieties were also significantly different (P < 0.05). The most susceptible maize variety, Kilima, produced about twice as many F1 adults as the least susceptible variety, ICW. Insect feeding also caused Kilima to lose about twice as much weight as ICW. There were positive linear relationships between weight loss, and indices of susceptibility; starch content and the indices of susceptibility (regression equations :- y = 8.927 + 0.342x and y = 3.485 + 0.248x respectively). Grain hardness was negatively related to the indices of susceptibility (y = 18.77 - 0.098x). Grain hardness and starch content of the maize were also negatively related .(R = - 0.91). The protein and moisture contents and the grain weight of the maize varieties were not significantly related to the indices of susceptibility. The study shows that those varieties of maize tested had different levels of susceptibility to P. truncatus feeding and that some were less palatable to the insects. It is therefore recommended that further research be carried out with the objectives of producing recommendations for maize with better storage characteristics, by including grain borer resistance parameters in the maize breeding programme, to provide farmers with varieties better able to resist P. truncatus damage: