Book lice

Book louse
Liposcelis sp.
Systematics
Superordinate : New winged wing (Neoptera) Order : Dust lice (Psocoptera) Subordination : Troctomorpha Family : Liposcelididae Genre : Book louse
Scientific name
Liposcelis
Motschulsky , 1852

The book lice (genus Liposcelis ) are insects of the order of the dust lice ( Psocodea or Psocoptera); there the suborder Troctomorpha . Although closely related to these, they do not belong to the class of lice . They are widespread and often found in apartments and are considered nuisances there , but in some cases as significant pests in grain stores . Some species also live in the wild. Unlike lice, they are directly harmless to humans ( apart from allergy sufferers ), in particular they do not suck blood. Colloquially, they are also known as paper lice .

features

Book lice are small, wingless insects with a body length of about 0.6 to 1.8 millimeters, they are colored from yellowish translucent to brownish and sometimes inconspicuously drawn by ribbons. The body is flattened dorsoventrally (from top to bottom). Like almost all dust lice, they have a rather large, hemispherical and very flexible head in relation to their body size with a protruding and enlarged postclypeus . The complex eyes are small and consist of 2 to 8 ommatidia , point eyes ( ocelles ) are absent. The antennae are relatively short and consist of 15 segments, the segments of the antenna whip are secondary curled. The mouthparts consist of two triangularly shaped, biting mandibles with a plate-shaped molar region (for grinding food particles) and a simple tip, strongly modified maxillae with a rod-shaped elongated inner chamber ( lacinia ) and a labium with greatly enlarged paraglossae . The Laciniae presumably serve as chisel-like scraping and thrusting tools. The maxillary palps are four-limbed, the labial palps two-limbed.

The trunk consists of a short prothorax and the fused meso- and metathorax . In plan view, the prothorax is divided into three parts with a central plate and two lateral sclerites (lateral lobes). The three pairs of legs are somewhat flattened. The shape of the hind legs is characteristic of the genus. These are flattened and greatly broadened, at the widest point they have a clearly offset hump on the front edge. The tarsi are tripartite.

The abdomen is elongated oval shaped and consists of nine clearly distinguishable segments. At the rear end, the females carry a short, partially reduced ovipositor , which is covered by the subgenital plate . In many species, males are rare or unknown ( parthenogenesis ); the first males were discovered in 2008 in the pest Liposcelis bostrychophila , which is widespread worldwide . If there are males, they can be recognized by the fact that they are usually paler in color and smaller than the females.

development

Book lice have direct development that resemble larval stages, apart from their size, to imaginal insects and can hardly be distinguished from them on superficial inspection. The development begins with an egg, which is quite large in relation to the body size; it reaches a third of the body length of the female. Eggs are glued to substrate particles. The number of larval stages varies between species and within the same species, with one stage more being given for females than for males in many cases. Details are z. B. for Liposcelis rufa and Liposcelis brunnea : two to five larval stages, and for Liposcelis entomophila and Liposcelis bostrychophila : three and four larval stages respectively. The development time from the egg through all immature stages to the new imago is between 16 and 25 days for females under favorable conditions, and slightly less for males. The lifespan of the animals is strongly dependent on temperature, it can be between about 20 and 80 days, whereby the development cycle is greatly extended and delayed at cooler temperatures. With poor quality food and cool temperatures, a maximum lifespan of 53 weeks (with greatly reduced reproduction rate) was observed. Egg production per female varies between around 40 and 110 eggs, depending on environmental conditions.

Biology and nutrition

The diet and way of life have been researched almost exclusively in the synanthropic species that are significant pests, while almost nothing is known about the wild species. Contrary to older views held up to the 1990s, book lice can, like almost all other dust lice, feed on hyphae of (mold) fungi, but they do not depend on them for food. In particular, they are able to feed on intact and unpeeled cereal grains as an exclusive food basis. In addition, a large number of more or less suitable food substrates have been identified. Many species are obviously not picky about their food, even if there are usually clear preferences for plant-based products with a higher moisture content.

As expected, the preference conditions for book lice differ depending on the species. Most of the species known from households and stores show the highest reproduction rates at relatively high temperatures. Optima around 30 ° C were determined for most species. But they are able to reproduce successfully over a wide temperature range (from below 20 to over 40 ° C). In any case, the animals are very dependent on moisture. They cannot exist below 40 percent relative humidity, at 50 percent only in the optimal temperature range. Depending on the species, optimal conditions of 60 percent (for Liposcelis brunnea ) to 80 percent were determined, while even higher humidity is disadvantageous again.

In heated houses and households, apart from supplies, dust lice in Central Europe are therefore dependent on areas with higher humidity. They are most commonly found in bathrooms (confirmed in a Spanish study). Often you can find them at floor drains (gullies). You can with increased humidity, z. B. in basement rooms, on cool outside walls or in freshly plastered new buildings, but occur almost everywhere, often z. B. on or under damp, wavy wallpaper. They are extremely common in homes here, but not always noticed because of their small size. In a study in England they were found in 15 percent of all kitchens examined. While Liposcelis bostrychophila was by far the most common species in households in England and the Czech Republic , Liposcelis decolor and Liposcelis brunnea dominated in Spain .

Seasonally, book lice occur in houses all year round, the highest densities are usually reached in midsummer (July and August).

The animals owe the name "book lice" to their occurrence in books that have been stored in moisture. It can be assumed that this was not or is not actually a focus of distribution, but that the animals that are widespread in the household are most likely to reveal the existing infestation through their movement on flipped pages. While more damage to books by animals is not known - the problem here is probably the moisture itself and the associated mold infestation - it can sometimes cause massive damage to museum collections, e.g. B. insect boxes, arrange.

A number of predatory mite species are known to be predators of book lice . The book scorpion also feeds on book lice, among other things.

Economic importance

In households, dust lice are more likely to be a nuisance, where they rarely cause economic damage. Due to their high moisture requirement, they are more an indicator of a wetness problem (with mold and mold spores) than a problem themselves. Today, however, they are considered to be significant pests in grain stores, in some countries, e.g. B. Australia, as the most economically important grain pest ever. Their significance as a stored product was only recognized late. In the early 1990s, they were considered almost insignificant. It is debatable whether this is due to an actual change, e.g. B. the introduction of the species Liposcelis bostrychophila, which originally came from tropical Africa, is declining almost worldwide, or whether the pre-existing damage was only underestimated or not noticed. The species are difficult to detect because of their small size and were originally (erroneously) considered to be linked to mold infestation. Book lice can cause weight loss of up to 10 percent in stored grain.

In households, book lice are often found in stored supplies. Flour stored in paper bags in particular ( hygroscopic , with a water content of typically around 12 to 14 percent) is almost an optimal feed and, laid out in small paper bags, can be used as bait for detection of infestation. Dust lice , especially Liposcelis bostrychophila , are at the forefront of consumer complaints about pests in flour and grain products.

Prevention and treatment

It is difficult to control dust lice in grain stores. Among other things, the animals have developed resistance to numerous approved pesticides . In apartments, the infestation is to be counteracted by addressing the cause of existing moisture problems. Direct control is possible with commercially available insecticides ( pyrethroids ), but is rarely advised, as an immediate new infestation would be expected without eliminating the cause. As an immediate measure, frequent and extensive ventilation is recommended, but the success is not checked or scientifically proven. During the scientific studies on the occurrence in apartments, u. a. No association with an occurrence was found for the following factors: keeping of pets, number of house plants, height and frequency of trees in the vicinity of the home, storage or shopping habits. A possible infestation has nothing to do with cleanliness or hygiene in the home. The animals are often brought in through infected food packages while shopping.

In the event of an infestation of supplies (food), the disgust factor is decisive, direct health consequences are not to be expected. If necessary, the animals can be killed by heating them in the oven to 70 ° C or freezing them (longer than a week).

Taxonomy and systematics

Book lice are widespread around the world, and many species have been dragged out of their original range by humans. For example, 10 species are considered neozoa in the Czech Republic . For some species, however, the original range is controversial and may hardly be reconstructable.

The genus Liposcelis comprises a total of 126 valid species, of which at least 34 are expected in Europe. There are also a number of inconsistently introduced species as well as those whose species specification in the literature or taxonomic status is dubious. Only a few species are found in homes or storage facilities in Europe. In England, only Liposcelis bostrychophila and L. corrodens were common in apartments, two other species ( L. decolor and L. mendax ) were rare. The most common species living in the wild in Germany is Liposcelis silvarum .

If one restricts oneself to the most common synanthropic species, an assignment up to the species with an American image identification key can be attempted. A precise identification of the species is difficult and demanding and can only be carried out by specialists under the microscope. In addition, the most common species occur in local populations that differ slightly in terms of morphology and way of life. In order to make the determination easier for practitioners, attempts are being made to develop molecular methods (cf. DNA barcoding ).

The genus Liposcelis ( type species : Liposcelis brunnea ) is assigned to the family Liposcelididae (older name: Liposcelidae) and therein to the subfamily Liposcelidinae: with the exception of a single, cave-dwelling species ( Troglotroctes ashmoleorum ), the systematic position of which is uncertain, it is the only genus this subfamily. The species of the genus are grouped into four species groups for identification purposes, but their monophyly is doubtful.

According to recent findings, the Liposcelididae are more closely related to the lice than to the other dust lice. It is believed that the lice (in the Cretaceous Period) developed from book lice-like ancestors who moved from a way of life in nests or beds to a parasitic way of life. The exact relationship is still controversial. Research is made more difficult by the fact that the mitochondrial DNA , which is often used for comparison purposes, is greatly modified in this group. In Liposcelis bostrychophila , the usual single chromosome of the mitochondrion is split into two separate chromosomes; in the human louse Pediculus humanus , each of the 20 genes even forms its own small chromosome.

Fossils

The genus Liposcelis is known with a fossil representative ( Liposcelis atavus ) from the Baltic amber (late Eocene , around 40 million years old). Probably a fossil originally described in a different genus ( Embidopsocus eocenicus ) made of amber from the Paris Basin (early Eocene, around 53 million years old) actually belongs to it. This would be the oldest known evidence.

literature

• TR New: Psocids: Psocoptera (Booklice and Barklice) (RES Handbooks for the Identification of British Insects). Vol. 1, Part 7, London 1974.
• Matthias Schaefer: Brohmer - Fauna of Germany. 18th edition, Quelle & Meyer Verlag, Heidelberg 1992, ISBN 3-494-01200-8 .
• HJ Hannemann, B. Klausnitzer, K. Senglaub: In: Erwin Stresemann (Hrsg.): Excursion fauna for the areas of the GDR and FRG . Volume 2/1: Invertebrates, insects. 8th edition. Volk und Wissen Verlag, 1989.

Web links

• Website of the Psocodea Species File with a list of species
• USDA Psocid Picture Key

Individual evidence

1. ↑ Edward L. Mockford & Paul D. Krushelnycky (2008): New species and records of Liposcelis Motschulsky (Psocoptera: Liposcelididae) from Hawaii with first description of the male of Liposcelis bostrychophila Badonnel. Zootaxa 1766: 53-68.
2. ^ Edmund, CW Leong & SH Ho (1995): Life cycle of Liposcelis entomophila (Psocoptera: Liposcelididae) and a culturing regime for liposcelids . Bulletin of Entomological Research Volume 85, Issue 4: 501-506.
3. ↑ GP Opit, SG Gautam, BA Aminatou, JE Throne (2010): Ecological studies of the Psocids Liposcelis brunnea, L. rufa L. pearmani, and Lepinotus reticulatus. Proceedings 10th International Working Conference on Stored Product Protection. Julius Kühn Archive 425: 173-179.
4. ↑ JJ Wang, JH Tsai, ZM Zhao, LS Li (2000): Development and reproduction of the psocid Liposcelis bostrychophila (Psocoptera: Liposcelididae) as a function of temperature . Annals of the Entomological Society of America 93: 261-270.
5. ↑ ^{a b} G.P. Opit & JE Throne (2009): Population Growth and Development of the Psocid Liposcelis brunnea (Psocoptera: Liposcelididae) at Constant Temperatures and Relative Humidities. Journal of Economic Entomology Vol. 102 No. 3: 1360-1368.
6. ^ ^{A b} Bryan Turner & Naheed Ali (1993): Population variability in a domestic stored product pest, the parthogenetic Psocid Liposcelis bostrychophila: implications for control. Proceedings of the First International Conference on Urban Pests: 309-317.
7. ^ ^{A b} A. Baz & VJ Monserrat (1999): Distribution of domestic Psocoptera in Madrid apartments. Medical and Veterinary Entomology 13: 259-264. doi : 10.1046 / j.1365-2915.1999.00176.x
8. ↑ B. Turner & H. Maude-Roxby (1989): The prevalence of the booklouse Liposcelis bostrychophilus Badonnel (Liposcelidae, Psocoptera) in British domestic kitchens. International Pest Control Vol. 31 No. 4: 93-97.
9. ↑ ^{a b c d} B. Turner & N. Ali (1996): The pest status of Psocids in the UK. Proceedings of the Second International Conference on Urban Pests: 515-523.
10. ↑ Z. Kucerova (2002): Weight losses of wheat grains Caused by psocid infestation. Plant Protection Science 38: 103-107.
11. ↑ Udo Sellenschlo & Susanne Kolls: Preventing vermin and fighting them naturally . W.Ludwig Buchverlag, Munich 1996, ISBN 3-7787-3530-6
12. ↑ H. Šefrová & Z. Laštůvka (2005): Catalog of alien animal species in the Czech Republic. Acta Universitatis Agriculturae et silviculturae Mendelianae Brunensis Vol 53, No 4: 151-170.
13. ↑ Psocodea Species File online , accessed July 25, 2013
14. ^ C. Lienhard (1990): Revision of the western Palaearctic species of Liposcelis Motschulsky (Psocoptera: Liposcelididae). Zoological Yearbooks, Department for Systematics, Ecology and Geography of Animals Vol. 117 No. 2: 117-174.
15. ↑ USDA Psocid Picture Key
16. ^ M. Qin, Z. Li, Z. Kucerová, Y. Cao, V. Stejskal (2008): Rapid discrimination of common species of stored Liposcelis (Psocoptera: Liposcelididae) from China and the Czech Republic based on PCR-RFLP analysis. European Journal of Entomology 105: 713-717.
17. ↑ Qianqian Yang, Zuzana Kucerová, Zhihong Li, Irma Kalinovic, Václav Stejskal, George Opit, Yang Cao (2012): Diagnosis of Liposcelis entomophila (Insecta: Psocodea: Liposcelididae) based on morphological characteristics and DNA barcodes. Journal of Stored Products Research 48: 120-125.
18. ↑ ^{a b} Kazunori Yoshizawa & Charles Lienhard (2010): In search of the sister group of true lice: a systematic review of booklice and their relatives, with an updated checklist of Liposcelididae (Insecta, Psocodea). Arthropod systematics and phylogeny 68 (2): 181-195.
19. ↑ BM Boyd & DL Reed (2012): Taxonomy of lice and their endosymbiotic bacteria in the post-genomic era. In: Clinical Microbiology and Infection 18: 324-331. doi : 10.1111 / j.1469-0691.2012.03782.x
20. ↑ Dan-Dan Wei, Renfu Shao, Ming-Long Yuan, Wei Dou, Stephen C. Barker, Jin-Jun Wang The Multipartite Mitochondrial Genome of Liposcelis bostrychophila: Insights into the Evolution of Mitochondrial Genomes in Bilateral Animals. PLoS ONE 7 (3): e33973. doi : 10.1371 / journal.pone.0033973 (open access)