Description of Booklice
(Psocoptera)

Habitat
Domestic species prefers warm, humid conditions. Widely found in domestic kitchens and food premises. Usually on flour, other cereal products, milk powder. May need minute moulds in diet.

Biology
Egg - nymph - adult. Parthenogentic
Eggs relatively large, 2 per day, about 100 total per female, in crevices
Nymphs - 3–8 weeks to reach maturity, feed with adults. 
Adults - always female (not all species), l–1.5mm, pale brownish yellow, wingless (not all species are), "soft bodied" appearance. Lives about 6 months.

Importance
Nuisance and serious problem within food industry causing many customer complaints. Contamination of foodstuffs. Only small risk of health problems

Control
Difficult. Physical control. In domestic situations destruction of infested food material or freezing for a few days. Good hygiene and stock rotation may help

Distribution and Habitat

The great majority of the eight to nine hundred species of the Psocoptera live out of doors, feeding predominantly on yeasts, moulds and mildews. Some also feed on lichens and algae. Only a few species have been found commonly with stored foods or associated with the domestic environment, and again these are often attracted to foodstuffs and other materials which are damp and in which there is a degree of mould development. Distribution indoors, is therefore, usually dependent on high humidity which allows the fungal and mould development, which are essential dietary constituents for the booklice.

Biology

The most frequently found domestic psocid is Liposcel is bostrychophilus and its common name "Booklouse" is now often used to describe the whole order. It is pale yellow-brown in colour and wingless, although some species within the group do possess wings. It is found in domestic kitchens and is the most likely booklouse to be involved in customer complaints within the food industry. The species is parthenogenetic which means that the eggs are not fertilised and all adults are female. The female lays whitish, sticky eggs that she attaches to the food substrate and sometimes covers with fragments of detritus. An incomplete life cycle is followed, with between three and seven nymphal moults. Only slow development can take place at low temperatures and the optimum for this species seems to be around 25 to 30 °C, when a complete life cycle can take about three to four weeks. At 20 °C it may take up to 8 weeks. Feeding and behaviour are similar in nymphs and adults.

Another species, Lepinotus patruelis, prefers lower temperatures of between 15 and 20oC, is not parthenogenetic and is more commonly found in cooler environments such as grain stores and warehouses. It is a less prolific breeder than Liposcelis bostrychophil us but may damage grain and dried goods in long term storage.
Some of the common indoor species of booklice are known to produce regular tapping sounds by beating their abdomens against whatever they are standing on (most clearly heard on paper), and this may be related to their mating behaviour.

Importance

Booklice need to be distinguished from the true lice, which are described separately. They do not normally feed directly on human foodstuffs, and do not usually occur in significant numbers unless ambient conditions allow mould and fungal development. Physically damaged foods are seldom noticeable, but some fabrics and other delicate articles, for example dried insect collections, may be significantly damaged by booklice feeding on them. Additionally, even small numbers of these insects in a domestic environment might be unacceptable, and they frequently give rise to complaints to Environmental Health departments. Due to their very wide spread distribution it is seldom possible to prove whether booklice were present in the foodstuffs from the factory or shop, have entered the packets whilst in the domestic larder, or came from another source such as transport, pallets or packaging materials.

Control

In domestic situations, infested foodstuffs should be disposed of and surfaces cleaned with suitable household products. This will not kill or remove all eggs and infestations may recur. Storage of food in warm, humid conditions is likely to increase the likelihood of infestations developing and where possible cool, well ventilated larders should be used.

The use of insecticides is made difficult because Liposcel is bostrychophi I us has been shown to be tolerant to permethrin and probably to other pyrethroids, the most likely products to be used. Organophosphate compounds are far more effective and their use may be considered in some situations but their availability is reducing.

Lepinotus patruelis is susceptible to permethrin. In larger scale infestations fumigation may be considered but the eggs are relatively tolerant requiring higher concentrations of fumigant or longer exposure times.

In the food industry, food pallets are often considered to be one of the main means of distribution of psocids from one site to another. The application of a residual insecticide to pallets may reduce psocid populations significantly. Physical control by way of drying damp areas should always be considered.