Psocoptera

(invertebrate zoology) An order of small insects in which wings may be present or absent, tarsi are two- or three-segmented, cerci are absent, and metamorphosis is gradual.

(Book lice)

Class: Insecta

Order: Psocoptera

Number of families: 36 or 37

Evolution and systematics

Phylogenetically, the order Psocoptera (psocids, barklice, and booklice) is closely related to the Phthiraptera (lice), Thysanoptera (thrips), and Hemiptera (bugs, cicadas, aphids, etc). These four orders compose a monophyletic group, the Paraneoptera (hemipteroid insects), and psocids retain the most primitive features in the group. Within the Paraneoptera, psocids are most closely related to lice, with which they compose a monophyletic taxon, Psocodea. Furthermore, the family Liposcelididae (booklice) of the Psocoptera is regarded as the sister group of the Phthiraptera. Therefore, the order Psocoptera is probably a paraphyletic taxon.

The Psocoptera has been divided into three suborders, Trogiomorpha, Troctomorpha, and Psocomorpha. The Trogiomorpha consists of two infraorders and five families. The Troctomorpha, in which the Liposcelididae is classified, consists of two infraorders and eight families. The Psocomorpha, the largest suborder in the Psocoptera, consists of four or six infraorders and 23 or 24 families. Monophyly of suborders other than the Troctomorpha is well supported by morphology and DNA data.

The oldest fossil psocid is recorded from the lower Permian deposits in Kansas (about 290 million years ago). Fossil psocopterans in the Permian to Cretaceous periods represent extinct families. In contrast, fossil psocopterans in the Oligocene to Holocene periods are all assigned to extant families.

Physical characteristics

Psocids range from small (about 0.04 in/1 mm) to medium (about 0.4 in/10 mm) in size. Most of them are brownish or whitish with blackish brown markings, but some species of Caeciliusidae, Amphipsocidae, and Stenopsocidae have very colorful bodies and wings with markings. Morphologically, psocids are characterized by a well-developed postclypeus, long antennae, pick-like laciniae, a reduced prothorax, a well-developed pterothorax, and membranous wings (when present) held rooflike over the abdomen. The biting-type mouthparts with pick-like lacinia in psocids are considered to represent the intermediate condition between initial biting mouthparts in orthopteroids and the piercing and sucking type mouthparts in thrips and bugs, and this characteristic strongly supports the monophyly of the Paraneoptera. Psocids and lice share the specialized hypopharynx to uptake water vapor from the air, which supports monophyly of the Psocodea (psocids and lice). Most psocids are macropterous (fully winged), but brachypterous (short winged) or apterous (without wings) forms are also known.

Distribution

Psocids have been recorded from all zoogeographical regions, from tropical to subarctic zones.

Habitat

Psocids are found on a wide range of terrestrial habitat, such as on dead or living leaves, on stone or bark surfaces, and in leaf litter. Cave dwellers (such as Prionoglaris stygia) and wood borers (Psilopsocus mimulus) are also known. Some psocids are frequently discovered from food storage or other domestic environments.

Behavior

Most psocids are solitary, but the aggregation of larvae (e.g., Sigmatoneura, Psococerastis, and Metylophorus of Psocidae) or colony-forming psocids (including subsociality of Archipsocus) are also known. Some psocids weave silk nests of various shapes and sizes, and from one to numerous individuals may live under it.

Sound production in psocids is widely known. The sound is generally considered to be a courtship song, but this behavior is very poorly understood.

Feeding ecology and diet

Psocids feed chiefly on lichen, fungi, or organic debris such as flour and scurf (skin flakes).

Reproductive biology

Most psocids are bisexual, but parthenogenesis (thelytoky) is also known in 12 families of all three suborders. Courtship involves various behavioral patterns. Eggs are laid singly or in groups, and may be bare, covered with silk webbing, or encrusted with fecal material. A few psocids are viviparous (such as Archipsocopsis and Phallocaecilius species). Larvae hatch from eggs using a specialized egg-burster. The usual number of instars is six, but this is sometimes reduced to five, four, or rarely three. Psocids have no pupal stage.

Conservation status

No species of psocids are included on the IUCN Red List. Most leaf- and bark-dwelling psocids are common and seem to endure human influence. However, some psocids are clearly sensitive to human impact. For example, many psocids are endemic to a single small island; some cave-dwelling psocids are known only from a single cave; all species of the genus Psilopsocus are known to be rare, possibly because of their specialized wood-boring behavior.

Significance to humans

Most psocids live in the wild and are thus harmless to humans. Some domestic psocids, such as species of Liposcelis, are common household insects. Under warm, humid conditions, they can reproduce very rapidly, becoming serious pantry pests. Psocids also occur in stored food, and at high densities can contaminate foodstuffs. Domiciliary psocids are known to cause allergic responses in sensitized people.

Species accounts

Resources

Lienhard, C. "Psocopteres Euro-Mediterraneens." In Faune de France No. 83. Paris: Fédération Française des Sociétés de Sciences Naturelles, 1998.

Lienhard, C., and C. N. Smithers. "Psocoptera: World Catalogue and Bibliography." In Instrumenta Biodiversitatis, Vol. 5. Geneva: Museum d'histoire naturelle, 2002.

Mockford, E. L. "North American Psocoptera." In Flora & Fauna Handbook, No. 10. Gainesville, FL: Sandhill Crane Press, 1993.

New, T. R. "Biology of the Psocoptera." Oriental Insects 21 (1987): 1–109.

Smithers, C. N. "Keys to the Families and Genera of Psocoptera (Arthropoda: Insecta)." Technical Reports of the Australian Museum no. 2 (1990): 1–82.

Yoshizawa, K. "Phylogeny and Higher Classification of Suborder Psocomorpha (Insecta: Psocodea: "Psocoptera")." Zoological Journal of the Linnean Society 136 (2002): 371–400.

"Psocid as Pests" [March 31, 2003]. "PsocoNet" [March 31, 2003]. .

[Article by: Kazunori Yoshizawa, PhD]

An order of insects frequently referred to as the Corrodentia, or Copeognatha. Common names for members of this order are book lice, bark lice, and psocids, the latter a general term for all members of the order. They are usually less than 0.25 in. (0.6 cm) long, though rarely some may reach about 0.5 in. (1.2 cm). Wings may be absent, and when present are of differing distinctive venational types. Tarsi are two- or three-segmented, cerci are absent and metamorphosis is gradual. Chewing mouthparts usually have a much enlarged clypeus; the lacinia of the maxilla is usually elongate and chisellike, and the antennae have 13 or more segments.

Book lice are most common among old papers on dusty shelves, in cereals, or other domestic situations. They are usually pale, wingless types of insects. Many bark lice, the majority winged, occur on the bark or foliage of trees, and some are found under dead bark or beneath stones. Nymphs of a few species occur on tree trunks as clusters of gregarious individuals, but disperse when mature.

Psocoptera are worldwide, especially in warm countries, and some 1300 species are known. Current classification now lists about 27 families for this group. About 150 species, in 11 families, have been found in the United States. See also Insecta.

An order of insects; book lice found in dust and debris in many situations. Inconspicuous, soft-bodied insects which live on vegetable matter of various sorts and have no veterinary importance other than their ubiquity so that they are constantly suspected of causing disease.

Psocoptera Fossil range: 299–0 Ma PreЄ Є O S D C P T J K Pg N Early Permian - Recent
adult barklouse
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Subclass: Pterygota Infraclass: Neoptera Order: Psocoptera
Suborders
Trogiomorpha (7 families) Troctomorpha (9 families) Psocomorpha (24 families)

Psocoptera are an order of insects that are commonly known as booklice, barklice or barkflies[1]. They first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the hemipteroids ^[1]. Their name originates from the Greek word psokos meaning gnawed or rubbed and ptera meaning wings ^[2]. There are more than 5,500 species in 41 families in three suborders. Many of these species have only been described in recent years ^[3].

They range in size from 1 to 10 millimetres (0.039 to 0.39 in) in length.

The species known as booklice received their common name because they are commonly found amongst old books — they feed upon the paste used in binding. The barklice are found harmlessly on trees, feeding on algae and lichen. No member of this order is currently considered endangered; in fact, in 2007, Atlantopsocus adustus, a species native to Madeira and the Canary Islands, was found to have colonised the mild Cornish coast of southwest England.^[4]

Contents 1 Anatomy and biology 2 Classification 2.1 Suborder Trogiomorpha 2.2 Suborder Troctomorpha 2.3 Suborder Psocomorpha 3 References 4 External links

Anatomy and biology

Psocids are small, scavenging insects with a relatively generalised body plan. They feed primarily on fungi, algae, lichen, and organic detritus. They have chewing mandibles, and the central lobe of the maxilla is modified into a slender rod. This rod is used to brace the insect while it scrapes up detritus with its mandibles. They also have a swollen forehead, large compound eyes, and three ocelli. Some species can spin silk from glands in their mouth.^[5]

The forewings are up to 1.5 times as long as the hindwings, and all four wings have a relatively simple venation pattern, with few cross-veins. The legs are slender and adapted for walking, rather than gripping, as in the true lice. The abdomen has nine segments, and no cerci.^[5]

There is often considerable variation in the appearance of individuals within the same species. Many have no wings or ocelli, and may have a different shape to the thorax. Other, more subtle, variations are also known, such as changes to the development of the setae. The significance of such changes is uncertain, but their function appears to be different from similar variations in, for example, aphids. Like aphids, however, many psocids are parthenogenetic, and the presence of males may even vary between different races of the same species.^[5]

Psocids lay their eggs in minute crevices or on foliage, although a few species are known to be viviparous. The young are born as miniature, wingless, versions of the adult. These nymphs typically moult six times before reaching full adulthood. The total lifespan of a psocid is rarely more than a few months.^[5]

Classification

The Order Psocoptera is divided into three suborders.

Suborder Trogiomorpha

Trogiomorpha have antennae with many segments (22-50 antennomeres) and always three-segmented tarsi ^[6].

Trogiomorpha is the smallest suborder of the Psocoptera sensu stricto (i.e. excluding Phthiraptera), with about 340 species in 7 families, ranging from the monospecific fossil family Archaeotropidae to the speciose Lepidopsocidae (over 200 species). Trogiomorpha comprises Infraorder Atropetae (families Archaeotropidae, Empheriidae, Lepidopsocidae and Psoquillidae) and Infraorder Psocathropetae (families Psyllipsocidae and Prionoglarididae).

Suborder Troctomorpha

Troctomorpha have antennae with 15-17 segments and two-segmented tarsi.

Troctomorpha comprises the Infraorder Amphientometae (families Amphientomidae, Compsocidae, Electrentomidae, Musapsocidae, Protroctopsocidae and Troctopsocidae) and Infraorder Nanopsocetae (families Liposcelididae, Pachytroctidae and Sphaeropsocidae). Troctomorpha are now known to also contain the order Phthiraptera (lice), and are therefore paraphyletic, as are Psocoptera as a whole.

Some Troctomorpha, such as Liposcelis (which are similar to lice in morphology), are often found in birds' nests, and it is possible that a similar behaviour in the ancestors of lice is at the origin of the parasitism seen today ^[6].

Suborder Psocomorpha

Psocomorpha are notable for having antennae with 13 segments. They have two- or three-segmented tarsi, this condition being constant (e.g. Psocidae) or variable (e.g. Pseudocaeciliidae) within families. Their wing venation is variable, the most common type being that found in the genus Caecilius (rounded, free areola postica, thickened, free pterostigma, r+s two-branched, m three-branched). Additional veins are found in some families and genera (Dicropsocus and Goja in Epipsocidae, many Calopsocidae, etc.)

Psocomorpha is the largest suborder of the Psocoptera sensu stricto (i.e. excluding Phthiraptera), with about 3,600 species in 24 families, ranging from the species-poor Bryopsocidae (2 spp.) to the speciose Psocidae (about 900 spp) ^[6]. Psocomorpha comprises Infraorder Epipsocetae (families Cladiopsocidae, Dolabellopsocidae, Epipsocidae, Neurostigmatidae and Ptiloneuridae), Infraorder Caeciliusetae (families Amphipsocidae, Asiopsocidae, Caeciliusidae, Dasydemellidae and Stenopsocidae), Infraorder Homilopsocidea (families Archipsocidae, Bryopsocidae, Calopsocidae, Ectopsocidae, Elipsocidae, Lachesillidae, Mesopsocidae, Peripsocidae, Philotarsidae, Pseudocaeciliidae and Trichopsocidae) and Infraorder Psocetae (families Hemipsocidae, Myopsocidae, Psilopsocidae and Psocidae).

References

1. ^ Christopher O'Toole (2002). Firefly Encyclopedia of Insects and Spiders. Toronto: Firefly Books. ISBN 1-55297-612-2. 
2. ^ John R. Meyer (2005-03-05). "Psocoptera". North Carolina State University. http://www.cals.ncsu.edu/course/ent425/compendium/psocop~1.html. 
3. ^ Alfonso N. García Aldrete (2006). "New genera of Psocoptera (Insecta), from Mexico, Belize and Ecuador (Psoquillidae, Ptiloneuridae, Lachesillidae)". Zootaxa 1319: 1–14. http://www.mapress.com/zootaxa/2006f/zt01319p014.pdf. 
4. ^ BBC News, "New insect species arrives in UK" 8 November 2007
5. ^ ^{a b c d} Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 404–406. ISBN 0-19-510033-6. 
6. ^ ^{a b c} C. Lienhard & C. N. Smithers (2002). "Psocoptera (Insecta): World Catalogue and Bibliography". Instrumenta Biodiversitatis (Muséum d'histoire naturelle, Geneva) 5. 

External links

• National Barkfly Recording Scheme
• Psoco Net
• Tree of Life: Psocodea
• Archipsocus nomas, a webbing barklouse on the UF / IFAS Featured Creatures Web site

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