The definitive (and long!) answer -
King's College London
Psocids in the home
(B.D.Turner- text of a pamphlet written for the Pre-packed flour Industry)
WHAT ARE PSOCIDS?
To their dismay some people occasionally find that their food cupboards and especially dry goods such as flour, milk powder, sugar or semolina, have become infested with tiny grey or brown insects.They naturally, but wrongly, assume that the products themselves are always at fault.
Psocids are common but harmless household insects, between 1 and 2mm long, that can live in dry powdery type foods.
They do not like light or disturbance but prefer to live in dark, warm, humid places such as the folds of packaging in food cupboards.
They can live for about six months and in that time a female may lay up to 100 eggs. They can feed on a wide variety of dry food products from flour to cayenne pepper and also on the microscopic moulds that can develop in humid conditions.
They are not caused by poor hygiene; they are just as common in the cleanest of homes be they old or new.Research has shown that the sorts of psocids (there are several different types) that may cause problems in homes are rarely found where food is produced, so it is very unlikely that they get into the product during manufacture.
SO WHAT CAUSES THEM?
They prefer areas with a high humidity but can tolerate dry conditions for some days. Moisture in the home generally could be due to condensation from not having enough ventilation in the kitchen or bathroom. In new homes moisture is given off as plaster dries. Some food products, including flour, naturally contain some moisture. The kitchen is likely to provide the conditions they need, and fitted cupboards provide the darkness which attracts them.
In warm conditions they can rapidly increase in number. This is most likely to occur during the summer months when temperatures are higher. Any psocid problems are most likely to be noticed at the end of the summer.
HOW ARE THEY PREVENTED?
Try to deny them the conditions they need to survive and multiply- warmth and moisture.Always keep your dry foodstuffs, cereals and the like, in a cool, dry, well ventilated place.Clear out your cupboards regularly getting rid of old and outdated dry foods which may get pushed to the back of the cupboard.
If you clean the cupboards using water, always make sure they are completely dry before you put the food back. The edges of chipboard shelves that are hidden from view are usually unsealed. Use a mastic sealer to prevent psocids, and water getting into the chipboard.
When you are cooking or boiling the kettle or even just using the washing machine or tumble drier, make sure that the kitchen is properly ventilated.
If condensation shows on windows it is being produced on all other surfaces as well, and may lead to mould growth on which psocids can thrive.
HOW DO YOU GET RID OF THEM IF THEY APPEAR?
Remove the infested food immediately and dispose of it outside. Check everything else in the cupboard.
Any dry goods that look alright can be placed in a plastic bag and left in a deep freezer for 24 hours. This will kill any booklice or their eggs that may be present in the folds of the packaging.
Food in cans and bottles will still be all right but make sure that there are no insects hiding under the labels.
Clean out all the dust, crumbs etc. then make sure the cupboard is completely dry before using it again.
Foodstuffs in packets can be stored in jars, tins or other airtight containers.
Inspect your food cupboards regularly and repeat treatment if necessary.
Remember, prevention is better than cure.
Always store dry foods in a cool dry place.
