Interrelations among temperature, moisture, and viability of grain, and mites, insects, and fungi were studied from 8,135 samples collected at monthly intervals from two 13.6—ton wheat bulks stored in a granary at Winnipeg, Manitoba for 8 years during 1959—67. The bins were fumigated once with phospine (PH3) in August 1965, to determine the effect of the chemical on the existing relationships in the grain bulk ecosystems. Of the 32 possible principal components extracted from 32 variables by the principal—components method, the first 11, accounting for 65.6% of the total variability, were interpreted. The first principal component is a measure of general aging of the grain and fungal succession. The second and third principal components are measures of the major arthropod populations interacting with their physical environment. The analysis shows that Alternaria and its associates Gonatobotrys, Cochliobolus, Nigrospora, which are carried within seeds from the field, gradually disappear in storage and are replaced by Aspergillus versicolor, Aspergillus spp., Penicillium, Absidia, Chaetomium, Rhizopus, and Streptomyces. A grain mite Tarsonemus, which thrives mainly on Chaetomium, is the only arthropod that is positively correlated with the last group of fungi. The abundance of the granary arthropods, Cheyletus, Acarus, Glycyphagus, and Lepinotus is unaffected by time and most fungi, but appears to be regulated by a complex interaction of temperature, moisture, and, in some cases, the depth of the grain bulk. The predatory mite Cheyletus was related to its prey Glycyphagus and Lepinotus, but it did not effectively control the prey population. Interrelations among fungi and between some fungi and some arthropods in bulk grain ecosystems is confirmed statistically. The biological significance of the most important principal components and variables within these principal components are discussed.
