chapter 8

Psocodea (Bark/dust/book lice and their parasitic relatives) 8.1. Generalities and non-parasitic taxa

Bo. W. Svensson

The are an assemblage of small compris- Antennae usually long, 13 up to 50 segments. Basal flagel- ing free-living taxa (bark lice, dust lice, book lice) as well as lomeres with a weakened cuticle resulting in the ‘antennal taxa (chewing and sucking lice) which are ectoparasites on rupturing mechanism’, which like the specialized hypo- birds and mammals. Conventionally the free-living and pharyngeal sclerites also occur in the true lice. These parasitic lineages have been grouped under the names sclerites are involved in the ability to absorb moisture ‘’/‘psocids’ and ‘Phthiraptera’ respectively. It has from atmospheric vapour very effectively, a unique ability long been recognized that the parasitic lice are phylogenet- among insects in the adult stage. Prothorax is reduced, ically subordinate in the free-living psocodeans, and recent mesothorax enlarged. Macropterous, brachypterous, molecular and morphological analyses (Johnson et al. 2004, micropterous or apterous. Yoshizawa & Johnson 2006) indicate that the parasitic life- Most taxa of the most diverse group, , style has evolved independently in two lineages, viz., in the are macropterous (forewings extended beyond the tip of and in the + Anoplura (+ the extra- abdomen), but in some only males are long-winged. limital Rhynchophthirina). The most overall generalized Normally two pairs of membraneous wings, with relatively psocodeans are winged, but wings have been lost on a num- few cross-veins. The presence and shape of the character- ber of occasions within the free-living lineages and they are istic cell ‘areola postica’ has considerable taxonomic rele- consistently absent in the parasitic lice. Free-living taxa vance. The wings are usually held steeply roof-like, but in feed on fungus hyphae and other organic material; they are they are hold flat over the abdomen (espe- occasionally indoor pests. It is easy to propose plausible cially when moving). Legs slender, tarsi two- or three-­ scenarios of taxa living on debris in mammal dens and segmented, pretarsal claws usally with basal appendage, birds’ nests giving rise to the ectoparasitic lineages. The pulvillus, and in many families an apical tooth. Hind coxa principal diagnostic features of the Psocodea are found in of many species with a Pearman’s organ, a supposed strid- mouthpart features (hypopharyngeal sclerites in particu- ulatory mechanism. Abdomen membraneous except for lar) which are not visible without dissection. Like the the last two or three segments which are usually well scler- Thysanoptera and the Psocodea have few (three otized. In some species the sclerotized terga 8–10 or 9–10 or fewer) tarsal segments and lack cerci. The few Greenland form a clunium,­ sometimes of taxonomic importance. free-living psocodeans are indoor synanthropists and are Psocids occupy a wide range of habitats, from living as immediately recognizable by the prominently bulging indoor synanthropists (dust lice, book lice) to outdoor anterior part of the head (the clypeus). living in ground litter, but most are represented on bark ‘Psocids’ comprising the dust lice (), book or foliage of dead or living trees and shrubs (bark lice). lice () and bark lice (Psocomorpha), include Arboreal psocids usually have a broad range of tree spe- 4.400 described species (Lienhard & Smithers 2002), of cies specificity, but an ecological grouping seems evident. which 244 are recorded in Europe (Lienhard 1998) and 82 Thus, some taxa are clearly predominant on conifers and species in the Nordic countries (Svensson 2010). others on deciduous trees, whereas many appear indiffer- ent. Some species, however, show clear preferences within these two major habitat categories (Svensson Adults 2010). Rather few taxa are mainly found on low vegeta- tion, e.g. grass and herbs, and may then be difficult to sep- Adult ‘psocids’ are of superficially varying general appear- arate ecologically from those of ground litter and from ance, but share a number of characters. Soft-bodied and shrubs or small trees. Many species of Trogiomorpha and small (body length 1–6 mm). Orthognathous or progna- Troctomorpha predominantly occur indoor, often in thous, head mobile with a characteristic large and bulging stored products, e.g. grain and flour (not rarely as pests in postclypeus. Mouthparts chewing with robust and slightly warehouses in the tropics), old furnitures and books etc. asymmetric mandibles. Lacinia typically rod like, shape Several species, including some Psocomorpha, have also not rarely species specific. Eyes from small to usually large; been documented from nests of insects (e.g. bees and ocelli normally three, or absent (apterous taxa or morphs). ants), birds and mammals.