Psocids

Psocoptera (= Corrodentia). Barklice.

Psocids (New 1987) are free-living insects that feed on microflora and organic debris on surfaces of vegetation or on other surfaces. The range of food includes fungi (hyphae and spores), yeasts, lichens, or fragments of animal or vegetable matter. Most are arboreal (Thornton 1985) and are found on the bark or leaves of trees, but many also occur in ground litter. There tends to be a higher proportion of leaf frequenters in the canopy than near the ground in Neotropical forests that have been sampled for psocids (Broadhead and Evans 1979, Broadhead and Wolda 1985, Woldaand Broadhead 1985). Somedwellin the nests of mammals or birds, but none are parasitic like their close relatives, the biting and sucking lice. Members of the family Trogiidae make sounds by drumming the abdomen against the substrate. Psocids are frequently gregarious as nymphs or adults or both and may even group together under a communal web.

Several cosmopolitan types are commonly found indoors under humid conditions and are considered household pests. These are sometimes called "booklice" (fig. 5.14c) because of their habit of feeding on paper, sizing, and glue in book bindings (Broadhead 1946). They are minute insects (BL 1 mm or less) but are usually noticeable against a white paper background. All are similar wingless (or near wingless) forms brownish in color, and with slender legs There are several species whose proper names are confused in the literature. The widely used name Liposcelis divinatoria has been declared invalid by psocid taxono-mists; L. bastrychophila is the species to which it formerly referred (Lienhard 1990). These insects are apparently widespread in Latin America, but the real extent of their occurrence has not been documented because of a lack of collecting and the uncertainty of their identification.

Psocids are related to lice (Lyal 1985) and are louselike in general appearance, but adults usually have wings that are held rooflike over the abdomen when at rest. The wings have few veins, and the fore pair are much larger than the hind pair. Polymorphism is common in some families, the usual alternate form involving the reduction or loss of wings. A unique development is the bulging clypeal region on the front of the round head, which is unusually movable at the neck for an insect. The prothorax is reduced. The legs are slender and simple with a reduced number of tarsal segments.

Although some common pest species are minute, most wild psocids are small (BL 1—2 mm) and drably colored, gray or brown, frail insects. In humid tropical lowland forests, there are some much larger and quite colorful forms. Poecilop-socus iridescens, Psocidae (fig. 5.14b), of Amazonian Peru is approximately 12 millimeters long, with dark blue, white, and red wing markings and long antennae. Possibly, they are mimics of mirid or reduviid bugs (Mockford pers. comm.).

This is a much larger order in Latin America than indicated by published lists (e.g., Smithers 1967). At present, there are at least 780 species described in 96 genera and several hundred more that are certain to be found (Mockford pers. comm.). Some speciose, typical regional genera are Thryso-phorus, Ceratipsocus, and Graphocaecilius.

A great many species certainly are undiscovered in the tropical portions of the region- As with other insect groups, there is a progressive increase in psocid diversity from temperate to tropical forests (Broadhead 1983). Some show amphinotic Gond-wanaland distributions with close relatives ¡n Australia (e.g., Drymopsocus, Elipsoci-dae), but the southern temperate groups are mostly endemic and distinct from the rest of America to the north (New 1987).

References

Broadhead, E. 1946. The book louse and other library pests. Brit. Book News 68: 77-81. Broadhead, E. 1983. The assessment of faunal diversity and guild size in tropical forests with particular reference to the Psocoptera. In S. L. Sutton, T. C. Whitmore, and A. C. Chadwick, eds. Tropical rain forest: Ecology and management. Blackwell, Oxford. Pp. 107-119.

Broadhead, E., and H. A. Evans. 1979. The diversity and ecology of Psocoptera in tropical forests. 4th Int. Symp. Trop. Ecol. [Pan-| ama] Acta 1: 185-196.

ff, Broadhead, E., and H. Wolda. 1985. The M diversity of Psocoptera in two tropical forests fk in Panama. J. Anim. Ecol. 54: 739-754. jfj Lienhard, C. 1990. Revision of the western IE Palaearctic species of Liposcelis Motschulsky Si (Psocoptera: Liposcelidae). Zool. Lb. Sys.

Lyal, C. H. C. 1985. Phylogeny and classifica-K lion of the Psocodea, with particular refer-4P ence to the lice (Psocodea: Phthiraptera). B Syst. Entomol. 10: 145-165. Hp New, T. R. 1987. Biology of the Psocoptera. B Oriental Ins. 21: 1-109. hi Smithers, C. N. 1967. A catalogue of the Pso-■t coptera of the world. Austr. Zool. 14: 1-145.

Thornton, I. W. B. 1985. The geographical jH, and ecological distribution of arboreal Psocop-^B tera. Ann. Rev. Entomol. 30: 175-196. H Wolda, H., and E. Broadhead. 1985. Sea-^Ht sonality of Psocoptera in two tropical forests in Panama. J. Anim. Ecol. 54: 519-530.

These are all very small insects (BL of most ^^H 1-2 mm), although "giant" forms are found in the tropical forests of Latin America. The largest is the Peruvian Dasythrips regalis, which reaches a body length of 12 millimeters. The order is only recently becoming well known generally (Anantha-krishnan 1984, Lewis 1973).

Thrips are characterized structurally mostly by their unique wings; both pairs are very slender and elongate, without well-defined or extensive venation and with very long hair fringes. Many species are wingless, however, and other features, such as the asymmetric mouthparts located on a conical beak on the underside of the head, must be called on to define them. Only the mandible of the left side is developed and is used to punch holes in the epidermis of plants to release the sap, which is then sucked up. They also have a protrusible, saclike pad at the apex of each leg.

Most thrips live on plants, from which they take their liquid nourishment. The banana flower thrips (Frankliniella parvula; Harrison 1963) and others are often common on flowers, where their feeding may result in injured fruit; some hide in curled leaves (called queima in Brazil) or galls, which are caused by their feeding. The vegetarians may be very numerous and cause extensive economic damage to commercially valuable plants directly or by introducing pathogenic microorganisms. A large number of species are associated with the coconut palm (Sakimura 1986).

A very different group lives on dead twigs and among leaf litter and soil where they are predaceous on other minute insects and mites or feed on the fungi (hyphae and spores) associated with the early stages of decay (Mound 1977). Some of the predatory types are considered beneficial when they attack pests. An example is the black hunter (Leptothrips mali; fig. 5.14d), which takes all sorts of injurious insects, including aphids, scale insects, mites, and other thrips. Some species feed on termites. Thrips also are pollinators, for example, the banana flower thrips, which frequents the flowers of cacao in Trinidad (Billes 1941).

Development in some members of the order exhibits a parallel with that of the holometabolous insects, the last nymphal instar being quiescent and resembling a pupa.

The higher classification of the order has recently been clarified (Mound et al. 1980). Most of the eight families have Latin American representatives. However, primarily only the species with pest status are known. The majority belong to the two ubiquitous families Thripidae and Phlaeothripidae. These include some cosmotropical species such as the greenhouse thrips (Heliothrips haemorrhoidalis; fig. 5.14e), citrus thrips (Scirtothrips), tobacco and cotton thrips (Frankliniella and Thrips), gladiolus thrips (Taeniothrips simplex), and banana thrips (Chaetanaphothrips).

Native species are very poorly known in the region. A bizarre Mexican and Jamaican thrip is Arachisothrips, in which the leading edge of the fore wing is ballooned into a hollow, peanut-shaped outgrowth with a reticulate surface (Stannard 1952). It lives in rain forest ground cover, but the adaptiveness of this strange structural feature is unknown. One Brazilian species, with its nearest relative in Singapore, comprises the aberrant family Uzelothripidae. Franklinothrips vespiformis and relatives mimic various genera of ants in Mexico (Johansen 1983).

References

Anathakrishnan, T. N. 1984. Bioecology of thrips. Indira, Oak Park, Mich. Billes, D. J. 1941. Pollination of Theobroma cacao L. in Trinidad, B.W.I. Trop. Agric. (Trinidad) 18: 151-156. Harrison, J. O. 1963. Notes on the biology of the banana flower thrips Frankliniella paruula, in the Dominican Republic. Entomol. Soc. Amer. Ann. 56: 664-666. Johansen, R. M. 1983. Nuevos estudios acerca del mimetismo en el género Franklinothrips

Back (Insecta: Thysanoptera), en Mexico. Inst. Biol. Univ. Nac. Aut. México Ann. (Ser Zool. 1) 53: 133-156.

Lewis, T. 1973. Thrips, their biology, ecology and economic importance. Academic, London.

Mound, L. A. 1977. Species diversity and the systematics of some New World leaf litter Thysanoptera (Phlaeothripinae; Glytothri-pini). Syst. Entomol. 2: 225-244.

Mound, L. A., B. S. Heming, and J. M. Palmer. 1980. Phylogenetic relationships between the families of recent Thysanoptera (Insecta). Zool. J. Linnean Soc. 69: 111 — 141.

Sakimura, K. 1986. Thrips in and around the coconut plantations in Jamaica, with a few taxonomic notes (Thysanoptera). Fla. Entomol. 69: 348-363.

Stannard, L. J. 1952. Peanut-winged thrips. Entomol. Soc. Amer. Ann. 45: 327-330.

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