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The psocid or louse of the book

The psocid, commonly known as the book louse, is a small insect (1 to 3 mm) that easily enters homes. He adores books and all vegetable substances. He is also very fond of mold. If it settles in your home and finds favorable conditions there, it can quickly become invasive and cause damage. Discover in this file a set of answers and natural products that will allow you to best fight against this insect.

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Get to know the psocid better

(identity, mode of feeding, reproduction, ...)

Fight against psocid

(methodology of action, natural insecticides, ...)

Who is the psocid of the houses ?

psocid or book lice

Common name : Psocids, book lice or soothsayer, bark lice, dust lice.
Order : Psocoptera
Family : Microptera or Aptera
Size : 1 to 3 mm. Rarely exceeding 6 mm
Location : outside or inside depending on the species
Period : all year round

Nearly 4000 species have been recorded worldwide. Most psocids live outside houses on bushes, tree bark, walls and in vegetation. They then feed on lichens and algae, without ever causing the slightest damage.

But certain domiciliary species, such as liposcelis, can settle in your home and can become food pests by infesting and spoiling (by their presence and their droppings) a whole variety of products of animal or vegetable origin: flour and cereals (they are incapable of attacking whole grains!), glue, mushrooms, dead insects, wax...

Apterous species, lacking ocelli. Cream to brownish gray in colour, not more than 1.5 mm long. The posterior femurs are swollen – characteristic of Liposcelis. One generation per month in summer, with a laying of about fifty eggs; the adult remains in preoviposition for 3 to 4 months in winter then lays about twenty eggs in winter: there are 6 to 8 generations per year.

It is actively hunted by the book scorpion, Chelifer cancroides (Pseudoscorpion).

Psocid life cycle

Females of some species of book louse can reproduce without being fertilized, with males suppressed, prevented from growing, or absent altogether. Each female can lay nearly 200 eggs during her lifetime. They are mostly deposited separately, at a rate of 1 to 3 per day. Being sticky, they are often covered with fragments of food or waste that adhere to their substrate. The soft, pearl-colored eggs hatch after about 1 to 2 weeks. The emerging nymphs are very similar to adults and go through 3 to 8 moults depending on the species to reach maturity after about 15 days. After each successive moult, the nymph looks more and more like an adult and its eyes, antennae and wings (if it has them) begin to develop.

Environmental conditions and food quality influence the rate at which psocids develop. The life cycle is usually completed after 1 month, with adults surviving up to 6 months.

Their small size and flattened body allow them to easily hide in cracks and crevices. However, they have a relatively thin cuticle which, coupled with a high surface/volume ratio, makes them unsuitable for surviving unfavorable conditions and in particular low humidity levels.

The psocid is not dangerous

Although it looks like a head louse, the psocid does not bite. Its presence is certainly annoying, but the book louse (Liposcelis decolor), does not generally cause significant damage in a house. On the other hand, when the conditions are very favorable, it can quickly become invasive and cause damage.

The ideal conditions for it to proliferate are heat and humidity. If you delete one of the parameters, it will disappear by itself.

Mold is his favorite dish. If you suppress mold growth, you take away its food. He also loves starch (bookbinding glue, wallpaper glue) and can eat anything of plant origin. They occasionally swarm in flour mills, stores, libraries and museums where they are known as "book lice" and greatly feared as they can cause considerable damage to books.

Below 35% humidity, psocid dries out and dies.

Psocid can be found in new, freshly carpeted or damp apartments. In general, it is introduced with furniture, boxes, books and paper, all of which can carry the micro-organisms on which it feeds. The psocid lives an average of 110 days and hides in the dark.

The book louse - Liposcelis decolor

Psocid and real estate

In buildings, psocids are a nuisance, especially as long as the materials are not yet dry and tiny molds and algae on which they feed, along with a few fungus-eating beetles, develop on their surface.

It has been observed, in North America, that psocids preferentially "inhabit" the apartments of the upper levels. These are the last, in fact, where the plasterers passed; moreover, it is there that the thermal amplitudes are the strongest. If the infestations persist or reappear, it is because moisture spots, even invisible ones, have appeared (defects, cracks, leaks, etc.): these are formidable indicators.

Psocid and humidity

Psocids prefer moist environments, although they are sometimes found in dry places. The body of species of the genus Liposcelis contains about 66% water in the presence of a relative humidity of 73%, but only 22% in the presence of a relative humidity of 33%.

It is this ability to use their own water supply that allows psocids to survive up to three weeks in a dry atmosphere. Placed back in a humid environment, they are able to rehydrate quickly. On the other hand, prolonged exposure (more than 3 weeks) to drought is fatal to them. For psocids, an atmosphere is considered dry if its relative humidity is less than 58% (species living indoors) or 70% (species living outdoors).

Beyond these critical thresholds, psocids use the energy from their food to transport water vapor through their bodies, which allows them to compensate for water vapor losses due to transpiration and to stabilize their body mass even in the absence of food containing water (Knülle and Spadafora, 1969). In very humid environments, psocids can survive six months to a year (Broadhead and Hobby, 1944).

How to eliminate the psocid and protect yourself from it ?

In nature, we will let the psocids live and we will protect their habitat.

Indoors, as this insect can hide everywhere (mouldings, baseboards, under floors behind partitions, pipes, ducts, etc.), it is not easy to carry out a truly effective treatment. The most suitable will be to use the Ecodoo insecticide aerosol containing pyrethrum and alcohol. Its very fine spray allows it to penetrate everywhere, drying very quickly and without staining. It will mainly be necessary to treat the areas where your books are stored. If it is a library, spray the insecticide then close the door.

Our 4J insecticide will allow him to not forget any surface and thus increase your chances of eliminating them. It will be necessary to dilute this concentrated product up to 5% (i.e. 50 ml of insecticide for 950 ml of water) in a sprayer. Apply the product by spraying on a maximum surface. It acts by contact on eggs, larvae and insects thanks to its natural formulation of vegetable pyrethrum added with potassium soap and essential oils.

In the field of fumigation, the Habitat Biovétol fogger will give good results on this type of insect. It is an automatic insecticide diffuser composed of active ingredients of plant origin (pyrethrum + geraniol), intended for the basic treatment of the habitat. Very volatile, the solution is deposited in the smallest recesses where parasites and insects lodge. Immediate and prolonged action. 3 different formats exist: 75ml for a treatment of less than 15m², 150ml, for a treatment of less than 30 m². Finally, 250ml, for a treatment larger than 30m².

Finally, diatomaceous earth, this silicon dioxide powder can help you effectively in the fight against psocid. It will act over a long period, because it has a dehydrating action on the insect, which will lead to its death. About 1 week after the treatment, the dehydrated insects begin to search desperately for water. In general, they die within 2 weeks of applying the treatment. Diatomaceous earth stays active as long as it stays dry. Try to sprinkle some in all the cracks, nooks and small holes, places of predilection and potential hiding places of the psocid. For an action in the smallest recesses, small holes and interstices difficult to access, prefer the diatom to be sprayed in the form of an aerosol.

4J Insecticide concentrate with plant...

4J insecticide concentrate to be diluted. Effective against a large number of crawling and flying insects in our homes. Available in...
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Fogger Habitat with plant-based active...

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But the most effective treatment remains to remove one of the two parameters that promote its proliferation : the humidity and heat.

It is better to make life impossible for them by drying out (below 50 to 60% humidity) the atmosphere and refreshing it: no more than 15°C. The ventilation of the accommodation, the humidity absorbers, the lowering of the heating, ... will favor their disappearance.

For the rest, a well done bagging will prevent the psocids of the foodstuffs from spoiling, by their nibbling but especially by their stains, the preserved foods. Of course, we will maintain the premises where we will not tolerate any seepage or damp stains. All these recommendations must be followed in particular by insect collectors, easy victims.

In summary, preventive measures against psocid

- Keep the humidity below 40%
- Ventilate closed rooms
- Fix leaking pipes
- Insulate pipes to prevent condensation
- Vacuum regularly and pay particular attention to cracks and crevices. If possible, seal these cracks and crevices with an appropriate product.
- Store flour, cereals and other foods in closed containers. If you find these insects in flour, semolina or cereal, discard the food.
- If books or other objects are infested with psocids, put these objects in the freezer for a few weeks. Freezing will kill insects.

The psocid in vidéo