Effects of Temperature on the Effectiveness of the Triple Layer Hermetic Bag against the Larger Grain Borer Prostephanus Truncatus (Coleoptera: Bostrichidae) and Maize Weevil Sitophilus Zeamais (Coleoptera: Curculionidae) In Stored Maize

Abstract

The study examined the effect of temperature on the effectiveness of the triple layer hermetic bag in controlling P. truncatus and S. zeamais damaging maize in the store and how the temperature affects the tensile strength of the polyethene material used. The specific objectives include determination of the moisture content, oxygen depletion rate and seed viability of the maize. Five (5) kilogrammes of local maize variety (Abrodenkye) with initial moisture content of 14.6% was used for the experiment to fill each experimental storage bag. Two insect species, S. zeamais and P. truncatus were introduced in the bag. Three (3) temperature conditions (38oC, 18oC and room temperature (27o-32oC)) were used to store the maize in triple layer hermetic storage bag with polypropylene bag as control. Destructive samplings without replacement were conducted every month for the period of six (6) months. Thousand grain mass (TGM) method of weight loss assessment was used to determine the weight loss of the grain monthly. Results showed significant difference (p<0.001) in weight loss among the different temperatures. Weight loss was least in the triple layer hermetic bag at 18oC (0.41% and 1.21% for S. zeamais and P. truncatus respectively while 38oC and room temperature (27o-32oC) recorded the highest weight loss 20.12% and 28.15% respectively. P. truncatus caused the highest weight loss of 28.15% and was more destructive based on the powder produced due to feeding while S. zeamais caused 20.12% weight loss at the end of six (6) months. Numbers of live insects were significantly different between storage bags in different temperatures and among temperatures for both insect species. Results of the tensile strength showed that high temperature increased the ductility of the polyethene material with time. The tensile strength increased to 42.2 from its initial 33.4 at the end of six months of storage. Relatively, low temperature maintained the tensile strength throughout the experiment. On the other hand, fluctuations of temperature at the room temperature decreased the tensile strength making it brittle, fragmented and unsafe for long term usage in such geo-climatic zones. Moisture content and seed viability were significantly different (P<0.001) among various temperatures and between storage bags. The hermetic bag infested with S. zeamais at 18oC recorded highest seed viability and P. truncatus infested maize in polypropylene bag at room temperature (27o-32oC) recording the least seed viability. The study further revealed that although high density polyethene depletes oxygen completely and is 100% efficient in controlling insects, it cannot be used for long term storage in high temperature zones because it increases the moisture content of the maize and promotes the build-up of mould. It is recommended that farmers should be made aware of the choice of hermetic bag to be used according to their climatic zones.