Interrelations among Physical, Biological, and Chemical Variates in Stored-Grain Ecosystems; a Descriptive and Multivariate Study

Abstract

The impact of insect infestation on certain biotic and abiotic variates of 10 wheat bulk ecosystems exposed to the extreme climates of the Canadian Prairie was studied by measuring these variates at monthly intervals during 1969 and 1970. In addition to an insect-free ecosystem (control), one set of bulks was artificially infested with Cryptolestes ferrugineus (Stephens) and Oryzaephilus surinamensis (L.) and the other set with Sitophilus granarius (L.) and Tribolium castaneum (Herbst). The changes in temperature, moisture, viability of the grain, grain weight, dust weight, various species of microorganisms and insects, the fat acidity value, and the uric acid content were measured monthly and analyzed separately by conventional descriptive and multivariate statistical methods (principal component analyses). The analyses gave a clear picture of the pathways of biological and chemical deterioration of the grain in the systems. In the control system the fungus Alternaria alternata decreased, Aspergillus versicolor and Penicillum spp. increased, probably causing a moderate rise in the fat acidity of the grain and a slight drop in the grain weight. In the 2nd system, although Cryptolestes and Oryzaephilus did not attack many sound kernels, insects polluted the environment with excreta and remains, and appeared to accelerate the deteriorative processes observed in the “control system.” In the 3rd ecosystem, Sitophilus and Tribolium thrived, adding new pathways which involved the creation of large amounts of frass, invasion of Streptomyces and bacteria, and further acceleration of the deteriorative processes.