The effect of three species of mites upon fungal growth on wheat.

Every week, for 20 weeks, the growth of naturally occurring grain storage fungi on wheat infested with the three commonest British grain storage mites, Acarus siro, Glycyphagus destructor and Tyrophagus longior, was compared with that on uninfested wheat. The number of colonies of the Aspergillus glaucus group per gram were always less on grain infested with mites than on uninfested grain. Penicillium spp. were also less numerous on grain which was infested with A. siro but did not appear to be affected by the other mites. In contrast, two fungi which are pathogenic to mites, Aspergillus restrictus and Wallemia sebi, were more abundant in the presence of certain mites. The former was associated with G. destructor, the latter with G. destructor and A. siro. The three species of mites either feed on the A. glaucus group and Penicillium spp., or inhibit them by an unknown secretion. Pathogenic fungi are probably avoided. Mites are therefore an important variable in studies on fungal growth during grain drying and storage.