Long-term effects of an insecticide on a stored-wheat ecosystem

Abstract

Two granaries near Winnipeg, each containing 141 of dry wheat, were filled in September 1982 and the impact of a contact insecticide on the ecosystem was determined monthly for 27 months. The wheat in one granary was treated with malathion prior to storage and the wheat in the other was left untreated. Variables monitored throughout each bulk included: introduced insect and naturally occurring mite numbers, seed germination, seed-borne mycoflora, insecticide residue levels, and seed temperature and moisture. There were significant differences (P < 0.01) in most variables within granaries between samples from the top of the grain bulk and 1-m depth. Multivariate analysis of variance indicated significantly more (P < 0.01) arthropods and more seed infection by the fungus Penicillium in the control granary. Principal component analysis of data from each granary on each sampling date indicated the first components, which accounted for most of the variation in the systems, mainly involved temperature, moisture, fungi, and insecticide (when present); the second components involved fungi; and the third components involved fungi and arthropods, even in the treated ecosystem. The presence of a contact insecticide in a stored-wheat ecosystem had significant effects on the faunal community and definite but less conspicuous effects on the mycofloral community.