| dc.description.abstract | The Larger Grain Borer, Prostephanus truncatus Hom (Coleoptera: Bostrichidae), is a serious , pest of farm stored maize. Postharvest maize insect infestation is a major constraint to food security, food safety and income generation in Sub-Saharan Africa because of significant yield losses and grain quality degradation. P. truncatus infestation has been reported to cause 35% weight loss in maize during storage. This insect pest is mostly controlled by use of pesticides however; this results in environmental and food safety concerns. Therefore, there is need to develop alternative management systems for the control of P. truncatus. The aim of this study was to develop an integrated system to control P. truncatus in stored maize using solar disinfestation followed by hermetic storage in Purdue Improved Crop Storage (PICS) bags. An initial study was carried out to determine the susceptibility of P. truncatus in infested maize to heat in a hot air oven. Maize infested with adult insects of P. truncatus was subjected to heat treatment in hot air oven at temperatures of 50, 55, 60, 65 and 70ﾰC for an exposure time of 30, 60,90 and 120 minutes at each temperature.
After the heat treatment the adult P. truncatus were kept for 3 days and mortality counts determined. The analysis of Covariance and Variance (ANCOVA) indicated a highly significant effect of temperature (p<O.Ol) and interaction of temperature and time (p<O.Ol) on mortality of the adults P. truncatus; however the effect of time was not significant (p>O.05). Therefore one way ANOVA was done for each exposure time separately. Heat treatment of 60ﾰC for 90 min, 65ﾰC for 60 min and 70T for 30 min resulted in 98.5,98, and 100 % mortality, respectively. Logistic regression analysis showed that the LT95 for 120 min and 60 min were 55.3 and 61.3ﾰC, respectively. Longer exposure times resulted in further significant reduction in lethal temperature values. Therefore, to achieve >95% mortality of P. truncatus, during solar disinfestation maize should be subjected to a heat treatment of 55- 60ﾷC for 1-2 hrs.
A second study was carried out to assess the effectiveness of solar disinfestation and hermetic PICS bagging of maize in controlling P. truncatus infestation over a six months storage period. Three sets of PIes bags, each comprising of 3 bags, were filled with clean solar disinfested maize (Tl); maize infested with adult P. truncatus for 7days and subjected to solar disinfestation (T2) and solar disinfested maize that was later infested with adults P. truncatus (T3). Three sets
of 3 polypropylene bags, each comprising of 3 bags, were filled with clean solar disinfested maize (T4); solar disinfested maize and infested with adults P. truncatus (T5) and maize that was not solar disinfested (e). After six months' of storage the oxygen levels in PIes bags treatments T1, T2 and T3 were at 6.82, 7.68 and 9.34%, while the carbon dioxide levels were 13.52, 12.75 and 9.88%, respectively. In the PIes bags, only 2 live P. truncatus were present in T2; while high counts of
live P. truncatus (52.00), P. truncatus larvae (68.67) and S. zeamais (74.33) polypropylene bags were present in T5. After six months of storage, the PIeS bags treatments were able to maintain the moisture content at the recommended storage level for maize of 12 - 13% than all treatments in polypropylene bags, where the moisture content was above 13%.
After six months of storage, the germination capacity for the polypropylene bags had dropped to 36.96, 12.71 and 36.88% for T4, T5 and e, respectively; while for the PIes bags the germination capacity was 78.13, 69.17 and 71.04% for T 1, T2 and T3, respectively. After six months of storage, the percentage weight loss of maize stored in PIeS bags was significantly different (p < 0.05) to that of maize stored in the polypropylene bags. For the PIes bags, there was percentage weight loss of 0, 1.07 and 2%, for T1, T2 and T3, respectively, while for the polypropylene bags, there was percentage weight loss of 36.33, 47.66 and 30.5%, for T4, T5 and C, respectively. There was no significant difference (p > 0.05) between T2 and T3, therefore, PICS bags do not need any integration with solar disinfestation and can preserve maize that has not been previously disinfested with solar energy. More studies are needed to confirm the results of the present study. Hermetic storage is an effective low cost-effective system for grain produced in the rural areas of developing countries.
Keywords: Maize (Zea mays L.), Prostephanus truncatus, heat disinfestation, hermetic storage, Purdue Improved Crop Storage (PICS) bagging | en_US |
