Mites are common pests in grain storages and mostly occur in damp or moist grain, residues, oilseeds and animal feeds. They are not readily seen because they are the size of specks of dust. Mites are not insects (which have six legs) but are related to ticks and spiders and have eight legs.
When present in large numbers mites appear as a moving carpet of brown dust on the grain, silos and sheds or on stacks of commodities, sometimes emitting a damp or pungent smell. The mould mite Tyrophagus putrescentiae (Schrank) is the most common grain storage mite.
The grain or flour mite, Acarus siro L. is also widespread and sometimes the ´straw-itch mite´, Pymotes tritici can cause problems in storages.
A predatory (and therefore, beneficial) species Chelyletus malaccensis Oudemans, is also encountered where the above species are present. Generally, 2-3 species are present in an infestation.
Damage caused by mites
Both the mould and grain mites cause direct damage by eating the germ of the grain and spreading fungi in the commodities. Heavily infested commodity becomes tainted with off-flavours caused by squashed mite bodies when it is moved or processed.
During heavy infestation from the mould mite, the dead and live mites settle as a brownish dust layer on stacks of commodities and floors of stores and emit a lemon-flavoured odour leading to the popular name ´Lemon-scented mite´. In this situation, they can cause discomfort to workers handling infested grain and packaged commodities. The ´straw-itch mite´ can cause severe dermatitis and allergic conditions in people handling infested commodities.