Grain storage - Psocid and mite pests
Two common grain pests are not seen usually because they are the size of specks of
Psocids (pronounced ‘so kids’, also called booklice) are tiny termite-like
Mites are related to ticks and spiders and have eight legs rather than the six
that insects have.
When present in large numbers they appear as a moving carpet of dust on the grain,
silos and sheds.
Psocids and mites thrive under warm, moist conditions. Under favourable conditions
of 30°C and 70% relative humidity, psocids will multiply by 25 times in a month, and
mites by 500 times in a month. Under these conditions the life cycle of psocids takes
21 days, and mites 8 days.
Because of their rapid growth in warm, moist conditions, they usually reach peak
numbers during late summer. They are more common in the higher humidity of
coastal regions than in drier inland areas.
Psocids and mites feed on many grains and grain products. Their feeding causes
damage only when numbers are high.
Many markets will not accept produce infested with psocids or mites. This reason is
sufficient to justify control measures.
Mites infest animal feeds, especially if the product contains molasses, and may taint
the feed making it unpalatable to stock. The mites produce a characteristic smell,
giving rise to the local name of ‘lemon-scented mites’.
Some mites may cause allergic rashes on workers handling infested produce, and so
are known as 'hay-itch mites'.
Psocids and mites are tolerant of all chemical control measures available for treatment
of grain and grain products. Reliance on chemical control alone will not work!
Strict hygiene practices in and around grain or produce storage and handling areas
are essential for control.
Remove and destroy unwanted, infested produce by burning or burying.
If infested produce is to be kept, fumigate as described below.
Clean up and destroy grain dust and grain residues at least weekly.
Clean grain storages and handling equipment before handling new, uninfested
Spray the walls and floors of warehouses and sheds with Alfacron, but do not
spray surfaces that come into contact with the grain or produce.
Because of their need for warm, moist conditions, psocid and mite numbers can be
kept low by:
reducing temperature below 20°C, for example by aeration, or
reducing moisture below 60% relative humidity or 13% moisture for cereal
grains, for example by drying.
Fumigation with phosphine, usually called ‘bombing with phostoxin’, will kill psocids
and mites only if it is done in a sealed, gas-tight enclosure. Apply 1.5 tablets per cubic
metre and leave the enclosure sealed for 7 days if temperature of the produce is
above 25°C, or 10 days at lower temperatures. Air the treated produce before it is
Mite eggs can survive fumigation, even in a gas-tight enclosure. Progeny emerging
from the tolerant eggs should be treated by a second fumigation a week after the
For more information see Grain storage and drying information .
File No. FS0439
Last Updated October 2000.