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Booklice
DESCRIPTION
Order: Psocoptera (‘winged like Psocus’
with ability to grind to pieces).
Characteristics:
Soft-bodied insects, rarely exceeding 6mm in length. Typical forms have
two pairs of membranous wings, but there is an evolutionary tendency to
loss of wings in many species. Antennae long and threadlike, with 12-
50 segments; compound eyes, poorly developed; biting mouth parts; tarsi
2 or 3 segmented, each bearing two claws; incomplete metamorphosis with
egg and nymphal stages.
Species characteristics:
Liposcelis bostrychophilus (bostrychophila)
Adults about 1mm long; colour, light brown; broad, flat hind femur; no
wing rudiments; abdomen flattened.
Liposcelis entomophilus
Colour, yellowish brown, with conspicuous dark reddish bands across abdomen.
Death Watch (Trogium pulsatorium)
Adults very active, about 1.5-2.0mm long; pale yellow or white in colour;
well developed eyes; wing flaps present; rows of dark spots on front margins
of some abdominal segments.
Lepinotus patruelis
Adults about 2mm long; colour, dark brown or black; wing flaps present.
DISTRIBUTION
Most booklice species are found in natural habitats such as animal nests,
tree trunk crevices, under bark (hence the alternative name of barklice)
and on leaves. However, those species that have achieved pest status are
widely distributed and often found in ware-houses, food manufacturing
premises, granaries and museums as well as domestic and retail premises.
Here they will infest materials of plant and animal origin including stored
food, plaster, leather, woodwork and even books.
Many species are cosmopolitan and their countries of origin are unknown.
Different species exhibit different temperature requirements. Thus Lepinotus
patruelis is frequently encountered in cool situations, e.g. warehouses,
whilst Liposcelis bostrychophilus, which is thought to have originated
from Africa, prefers warmer situations. In heated buildings continuously
brooded species (e.g. Liposcelis spp.) will continue to breed throughout
the year. Other species (e.g. Trogium spp.) produce only one generation
per year and may overwinter as nymphs.
SIGNIFICANCE
Psocids rarely cause damage directly by feeding and are virtually harmless
in small numbers. Large infestations, however, may cause significant damage
to delicate materials such as books and furs. Signs of spoilage of dried
meat have included holes and tunnels in which the insects hide plus a
covering of white powdery material and salt crystals.
The major problem posed by psocids is the nuisance which they cause. The
insects will contaminate raw or processed foods. They may contribute to
a gradual heating of grain stored in bulk with an eventual impairment
of its properties and reduction in its value. Contaminated products must
be identified and destroyed, which is time-consuming and wasteful. Eggs
may be downgraded because of spotting caused by the crushed bodies of
dark booklice, e.g. Lepinotus spp. Finished products may be infested in
retail premises or in the home, with a consequent loss of goodwill. Pallets,
dunnage and packaging may be infested and act as a source of infestation
of stored products.
Among the wide variety of commodities and materials which may be infested
by psocids are the following: bagged nuts, bat guano, chocolate, fish
meal, milk powder, museum specimens and books, oil seeds, processed cereals,
pollen, salami, skin scales, Springbok biltong, stored cereal grains,
sugar beet seeds, yeast and even damp plaster.
Although harmless to man, booklice are often confused with true lice and
therefore regarded with alarm. As well as infesting foodstuffs in the
home they may be encountered swarming over furnishings and walls, including
newly plastered surfaces which are still damp.
Clearly, materials of both animal and vegetable origin may be attacked
but the insects show an undeniable preference for micro-organisms, including
bacteria, yeasts, moulds and algae, and populations will develop more
successfully in damp conditions where these thrive. This close association
with micro-organisms results in these becoming entangled in their bodies
and in this way the insects are instrumental in disseminating the organisms
which cause spoilage.
LIFE-CYCLE
(based on that of Liposcelis bostrychophilus)
The females of some species of booklouse may reproduce without fertilisation,
the males being suppressed, dwarf or entirely lacking. During her life
each female produces some 200 eggs. They are usually laid separately at
a rate of 1-3 per day and, being sticky, become covered with fragments
of food or rubbish or adhere to the substrate. The eggs of some outdoor
species are however laid in batches and covered with a silken web. The
smooth, pearl-coloured eggs hatch in 1-2 weeks. The emerging nymph closely
resembles the adult and will pass through 3-8 moults depending on species
(four in the case of L. bostrychophilus) to reach maturity in about 15
days. With each successive moult the nymph becomes progressively more
like the adult as eyes, antennae and wings (if present) begin to develop.
Ambient conditions and the quality of the diet profoundly influence the
speed of psocid development. The life-cycle is usually completed in one
month, the adults surviving for up to 6 months. The insects are only moderately
well adapted to the environments they inhabit. Their small size and flattened
bodies mean that they can readily hide in cracks and crevices. They do,
however, possess a relatively thin cuticle which, coupled with a large
surface/volume ratio, means that they are not well adapted to survive
adverse conditions, and, in particular, low relative humidities.
CONTROL
a) Hygiene/management
Because of the opportunities for re-infestation, booklice are difficult
to control with insecticides. The most effective method of control is
to ensure that premises are thoroughly aired and dry, thereby deterring
the development of moulds and denying the insects their food source.
Commodities should be stacked neatly above the floor level using pallets,
away from walls and should not touch the ceiling. A gap between stacks
will allow for ventilation, regular inspection, cleaning and, if necessary,
treatment with insecticides. Badly infested commodities should be destroyed.
Infested pallets can be identified by ‘knocking out’, i.e. dropping a
pallet held end on about 75mm (3") above a sheet of white paper.
b) Insecticidal control
Booklice are susceptible to a wide variety of insecticides. The problem
lies in ensuring contact between the pests and the toxicant in order to
bring infestations under control.
Glossary of terms
Tarsus (Tarsi): Apical section of leg (the foot).
ADVICE
Valent BioSciences has an extensive range of products specifically formulated
for the control of flying and crawling insect pests.
Further information on all Valent BioSciences' household insecticide products
is available from:
Valent BioSciences Corporation
870 Technology Way
Suite 100
Libertyville, IL 60048
The greatest care has been taken to ensure the accuracy of the information
contained in this Fact Sheet. Under no circumstance, however, will Valent
BioSciences Corporation be liable in respect of any error or omission.
© Copyright Valent BioSciences Corporation 2001
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