Insect infestation sources in stored maize grain; what is more important resident versus incoming infestation?

Abstract

Most studies targeted pest control inside stores; incognisant of the population dynamics in the store vicinity; leading to product re-infestation. Distinction between storage insect pest source and sink grain patches is important for effective pest management strategies. We examined the role of resident versus incoming insect infestation in phosphine-fumigated closed or open and unfumigated closed or open maize farm stores. Grain quality measurements were recorded over 32 weeks for two storage seasons. Whether open or closed, fumigated grain had significantly lower (p < 0.001) grain damage and lower grain weight loss (p < 0.05) than unfumigated grain. Fumigated open stores had significantly higher (p= 0.004) grain damage and weight loss than closed ones. Grain damage was higher in unfumigated-closed than fumigated-open, evidence that resident infestation inflicted higher food loss than incoming infestation. Prostephanus truncatus, Cryptolestes ferrugineus and Tribolium castaneum had significantly higher populations (p < 0.001, p = 0.018 and p = 0.001; respectively) at bottom levels of unfumigated and fumigated grain (T. castaneum). Sitotroga cerealella and Sitophilus zeamais were significantly higher (p < 0.001) at the top of closed than open unfumigated compartments. Grain suffers less infestation and quality loss when it is a sink patch than when it is a source patch. Population build-up and ‘settling’ to inflict significant food loss takes longer for incoming compared to resident infestation. These results have ecological implications on postharvest IPM.