Tolerance of Different Maize Varieties And Wood Species Used in Maize Storage Structures in The Volta Region, Ghana to The Larger Grain Borer, PROSTEPHANUS TRUNCATUS (HORN) (COLEOPTERA: BOSTR

ABSTRACT

prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), the Larger Grain Borer (LGB) has become a serious pest of stored maize and dried cassava chips since it was first seen in Ghana in 1989. Studies on the tolerance of maize varieties and wood species used in the construction of maize storage structures in the Volta Region of Ghana to P. truncatus was made under laboratory and field conditions. Varietal resistance of maize to insects could be of great help to farmers, especially those who have not got money for chemical treatment. In field studies of farmers' barns, maize cobs with longer, tighter and stronger husks had much lower levels of LGB damage than others in the same barn. Selected cobs from farmers barn also showed that good husk is important in resisting penetration of LGB. In no-choice laboratory trials, weight losses for local and improved maize varieties due to LGB were determined. The most susceptible improved variety had 6 times the weight loss (19% in 40 days) of the most resistant local variety Hardness (that is seed coat) of grain showed no obvious relationship to resistance in dehusked cobs. Husk cover was significantly related to resistance (p= 0.005) in a laboratory trial on degree of husk penetration by LGB. This is likely due to physical qualities rather than biochemical factors as ground-up husks sent to the Natural Resources Institute (NRI), Chatham, England, showed no evidence of antifeedant properties. A survey of maize storage facilities used in the Volta Region, showed that the platform, inverted cone and kitchen stores were the most widely used (51%, 18% and 12% respectively of total stores surveyed). Other store types were the katchalla (grass mat store), room store and basket. The survey identified 19 wood species used as components of these stores with bamboo (Bambusa vulgaris L.) and oilpalm (Elaeis guineensis Jacq.) fronds being the most widely used in all the agro-ecological zones. The six most important woods (Bambusa vulgaris, Elaeis guineensis, Borassus aethiopium, Raphia hokerri, Azadirachta indica A. Juss., Chlorophora excelsa and Triplochiton sclerexylon K. Schum.) were chosen for further testing. None of these supported breeding of LGB in laboratory trials. However, adult LGB survived in all woods for 7 weeks. Farmers with LGB in their storage platforms may not be able to replace the wood before stacking the new maize. Two possible alternative strategies were explored: (a) leaving the platform long enough for the adult LGB to die or (b) smoking the empty platform to disinfest it. Adult LGB survived in infested -ii- platform left in the open air for 3 months after removal of maize. Smoking of LGB-infested bamboo platforms resulted in disinfestation of woods within 3 days with intense smoking and within a week when smoking was done to simulate farmer's cooking time of 7 hours a day alongside an oilpalm mat screened fireplace. However, without screen, smoking was ineffective: some live LGB were recorded even after 7 weeks.