Population dynamics of Psocoptera in farm-stored grain and oilseed

Population fluctuation and spatial distribution patterns of five species of Psocoptera were determined during 1959–1979 in 12 cereal and oilseed bulks stored for 2–6 years in granaries on Manitoba farms. Lepinotus reticulatus, Liposcelis bostrychophilus, Liposcelis liparus, Liposcelis rugosus, Liposcelis subfuscus, and other Liposcelis spp. naturally infested wheat, oats, and barley initially stored at 10.3–14.0% moisture content and rapeseed stored at 6.3–11.6% moisture content. Generally, psocids were sparsely distributed and occurred in all parts of the granaries throughout the year, but they were most common and abundant during late summer and autumn. Only one serious outbreak of psocids in general was observed during 1963–1964 involving L. reticulatus in two adjacent 13.6-tonne wheat bulks in one granary. Application of Iwao's mean density and mean crowding regression method revealed a clumped spatial distribution for this species; an analysis of variance of the data showed that insect number per sample varied significantly (P < 0.01) among samples from 3-, 30-, 61-, 91-, and 152-cm depths after 24, 36, 47, and 48 months of storage. Principal component analyses and stepwise multiple regression analyses of the data for these sampling dates indicated that the large population rise of L. reticulatus resulted from significant (P < 0.01) interaction among several variables including moisture content, fungi, and mites. L. bostrychophilus occurred regularly in low numbers in patches in wheat and rapeseed bulks during 31–65 months of storage; the maximum number per sample was 126, in rapeseed in September. Liposcelis liparus and L. subfuscus also occurred in low numbers in patches in barley and wheat bulks; their maximum number was 42 per sample, in wheat in October. Association of the psocid species with other stored-grain insects and mites is discussed.