Aspects of the Biogeography of North American Psocoptera (Insecta)

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T. cerrosillae
T. neoleonense Yoshizawa et al. N,6 T. quaesitum (Chapman)  The list is based on the classification used by Lienhard and Smithers (2002), modified by the work of Yoshizawa et al. (2006) and Johnson and Mockford (2003). See text (section 6) for explanation of letter/number combinations following species names.  Lienhard, 2003). The Chinese fauna is reported to contain 1505 species in 170 genera. The North American fauna is miniscule by comparison. A minor part of this difference may be due to over splitting at the generic and specific levels in the study of the Chinese material. Most of this huge difference must be due to historico-geographic and historico-climatic differences beyond the scope of this chapter.
Another comparison of interest is that of the Mexican fauna (faunal list in Mockford & García Aldrete, 1996)

Biological aspects of the Psocoptera affecting dispersal and distribution
Psocoptera, commonly called psocids or the bark lice, are small insects, adults from the area under consideration ranging in body length from 1 to 5 mm. They are neopterous, exopterygote, acercareous (definitions in Nichols & Schuh, 1989). Adults typically have two pairs of membranous wings, but many evolutionary lines have undergone selection for wing reduction and loss. The winged forms appear to be weak flyers (Mockford, 1962) but may be carried by wind (discussed below). Nearly all are oviparous, and although ovovivipary is known, it is restricted to only two species living in North America, both of the genus Archipsocopsis. Many aspects of psocid biology were treated by New (1987). Immatures (nymphs) are generally cryptic in color and sometimes in form against their substrate. They feed on epiphytic and epigaeic algae and lichens, as well, in some forms, insect eggs and remains of dead insects. Mouthparts are of the chewing type (cf. Triplehorn & Johnson, 2005) with laciniae developed as rods. The latter are thought to stabilize the heavy mandibles as they bite and chew through tough material. Some 50 species have adapted to living primarily or in part in human habitations, and some of these feed primarily on farinaceous products (cf. Mockford, 1991). Psocids of all postembryonic stages have a unique apparatus in the mouthparts allowing extraction of water from the atmosphere. This involves a complex hypopharynx with a pair of lingual sclerites that are extruded with their lower surfaces out of the mouth during periods of higher relative humidity following dry periods. Water molecules accumulate on these surfaces and pass to the foregut by capillarity and action of a cibarial pump (see discussion in Lienhard, 1998: 33 -36). This mechanism has probably allowed some forms to survive in desert regions and others to live in heated human dwellings during winter.

Seasonality and its adaptations
Psocids living in the northern portion of North America (Canada and the northern two to three tiers of US states) pass the winter in the egg stage. Eertmoed (1978) and Glinianaya (1975) www.intechopen.com found a temperature-dependent response of females to late-summer shortening of day length as induction of winter diapausing eggs. In northern Mexico and the extreme southern United States, numerous species of psocids are active throughout the year. In southern Arizona and southern California, several species have only a single generation per year, in winter, with eggs hatching in mid November to early December and adults appearing in late December and persisting through May (Mockford, 1984b and pers. obs.) Observations by D. Young in south-central Texas suggest a similar pattern for several species in that region (personal communication). Such a pattern permits the species to pass the hot, dry summers of these areas in the relatively persistent egg stage. Although no data are available, it is likely that an environmentally induced summer egg diapause is involved. D .J. Schmidt (unpublished MS thesis, Illinois State University, 1989) determined seasonal occurrence of 27 species of Psocoptera at the Archbold Biological Station, Lake Placid, Florida (south-central Florida). Fifteen species were winter-uniseasonal (peak of abundance between December and May). Seven species were summer-uniseasonal (peak of abundance between June and November). Three species appeared to be biseasonal, with a peak in December and a peak in June. A single species appeared to be non-seasonal, and seasonality of one could not be determined. Nearly all of the larger forms (Family Psocidae) were winter-uniseasonal.

Modes of dispersal
Unfortunately, this is an area about which little is known. Earlier literature on this subject was reviewed by New (1987). A regular period of flight activity is part of the life cycle of some species of psocids, but such flights usually involve only short distances. Some species are known to become part of the aerial plankton and are carried long distances in that way. A notable case is that of the (primarily) North American species Lachesilla pacifica Chapman. Thornton (1964) reported that a female of this species was taken on a ship's aerial trapping device, 835 km at sea from San Francisco and thought to be a genuine air capture. The species occurs regularly along the Pacific coast from Vancouver, B.C., to southern California (Mockford, 1993). Throughout that area it is represented by sexual and thelytokous (all female) populations. Temporary populations, always of the thelytokous form, become established in central Illinois and Kentucky, far to the east of the usual range (García Aldrete, 1973;Mockford, 1993). The species was also reported from the region of Geneva, Switzerland (Lienhard, 1989), where three females were taken in two successive years. In all of these cases, long-distance wind transport is the likely means of dispersal.
Other non-human modes of psocid transport, including phoresy on birds and mammals, reviewed by New (1987) are of interest, but have not been investigated in North America. Mockford (1991) listed and keyed 50 species of psocids known to live commonly in human habitations. Many of these are cosmopolitan in distribution and are known to be spread through human commerce. The region of origin of most of those species (those designated "C" in Table I) are not known and can only be suggested in some cases where species show close relationship to forms native or endemic to particular regions. Mockford (1993) proposed the following criteria to determine if a species has been introduced: (1) species commonly associated with human commerce are regarded as introduced unless they have an extensive out-door distribution in the study area;

Native versus introduced taxa
(2) species for which introduction into the study area has been documented and which are not, or scarcely, otherwise present are regarded as introduced; 3) species widely distributed elsewhere, and with a very limited, coastal distribution in the study area are regarded as introduced unless the distribution in the study area appears to be part of a natural distribution largely outside the study area. The species designated I and (dom) on Table I are regarded as introduced. Table 1, the synoptic list of taxa, includes for each species its status: native (N), intercepted at a port of entry (I, followed by no number), introduced or cosmopolitan and established in a particular area ( C or I, followed by a number), introduced or cosmopolitan but found only in human habitations [C or I, followed by (dom)]. The numbers refer to primary distribution patterns. Mockford (1993) recognized five of these for the North American psocid fauna. A sixth must be added for the extended definition of North America followed here. Following are the definitions of the patterns (see also map, Fig. 1).  and introduced forms, have adapted to the mesic, in some areas highly humid, habitats of the Pacific coastal plain. Some of those taxa range eastward into the Cascade Mountains and a few even into the Rocky Mountains. Some of them are taxa also represented in Pattern 1 (see also section 7). Thirty-five species are included in this pattern (Table 1, species designated N, 5; C ,5, and I, 5) or 9.0% of the North American fauna. 6. The North-Mexican Montane areas and surrounding High Plains. Unfortunately, the western part of this interesting pattern remains rather poorly explored, and some material in collections remains to be investigated. Sixty-four species are included in this pattern (Table 1, species designated N, 6) or 16.5% of the North American fauna. The percentages of the total fauna noted above only reach 91.1%. The rest of the faunal list consists of intercepts at ports of entry (I , and I(dom), followed by no number on Table 1), of which there are 34 species, and cosmopolitan domestic (i.e. in human habitations) species, of which there are six (C (dom) and IC (dom) on Table 1). Psyllipsocus ramburii forms something of an exception to all others, being a cosmopolitan species occurring commonly in human dwellings, but also occurring in caves throughout North America.

Speciation in sexual species
The overall impression of speciation in North American Psocoptera is that there has not been a large amount of in situ differentiation. Passing through Table 1 in systematic order, the first group suggesting speciation is the Echmepteryx hageni complex, with three species, E. hageni, E. intermedia, and E. youngi. Undoubtedly, they are closely related, but they are all www.intechopen.com part of a much larger Antillean complex, and, indeed, E. intermedia also occurs in Jamaica. It seems quite possible that each of the three species may have been derived separately from Antillean ancestors.
In the genus Rhyopsocus, the three species R. maculosus, R. micropterus, and R. texanus appear to be closely related. The speciation events that led to their separation probably occurred in northern Mexico and adjacent southern United States. These species inhabit ground litter and pack rat nests, where humidity probably remains higher than in the surrounding xeric lands. Rhyopsocus bentonae, a species of peninsular Florida, southern Georgia, and the Gulf coast to Texas is part of a complex, with a second species on the Florida keys and a third in southern Mexico. The two Florida species may represent range expansions at different times of more southern species with subsequent adaptive changes.
In the genus Psyllipsocus, there appear to be two examples of speciation within North America, but both are currently under investigation.
In the genus Speleketor, the speciation events leading to the establishment of the three known species may have occurred in southwestern United States, but nymphs of a presumed fourth species of Speleketor have been found in a cave in Nuevo León State in northern Mexico (pers. obs.).
In the Subfamily Embidopsocinae of the Family Liposcelididae, two species, Belaphotroctes hermosus and B. simberloffi, the former of woodland ground litter in southern Texas and northern Mexico, and the latter in red mangroves on the Florida Keys, appear to be closely related (Mockford, 1972). Their speciation may have resulted from breakup of a continuous range around the Gulf of Mexico. Mockford (1993) noted the close proximity of the Embidopsocus species of subgroup IB (see Mockford, 1993: 78). Speciation in this subgroup has resulted in two Brazilian species, a Cuban species, and three species in North America. Of the latter three, E. bousemani is restricted to hilltops in the extreme southwestern Appalachian Mountains and in the Ozark hills. Embidopsocus laticeps is a Florida and south coastal-plain species extending north into southern Georgia and west into Louisiana. The third species, E. mexicanus, occurs widely in southern Mexico and is known from two localities in southeastern Texas. Oddly, a single specimen was collected at Funks Grove in central Illinois. The species of Embidopsocus are subcorticolous, and one species in southeastern Asia was recorded as phoretic on a migratory bird (Mockford, 1967).
In the genus Liposcelis, L. pallida and L. villosa appear to be closely related and may have speciated in the mountains of southwestern United States.
In the Family Archipsocidae, Archipsocus floridanus and A. nomas are probably closely related, but both are known from areas to the south of the study area, and it is likely that their speciation did not occur within the study area. north and V. maritimus on the Pacific coast. In the genus Xanthocaecilius, X. microphthalmus appears to have budded off in an isolated mountain area in Nuevo León State from a much more widely distributed species, X. anahuacensis, which is found throughout much of Mexico and Central America (see Mockford, 1989).
In the Family Lachesillidae, two species of Nanolachesilla occur in southern Florida, both on dead leaves, but one, N. hirundo, is restricted to palms. Other species of this genus are known from Jamaica and southern Mexico. It is likely that these two species are not sister species and that their speciational events may have occurred elsewhere, at least in part. Lachesilla texana may offer an example of ongoing speciation. A population presumably isolated in the southern Appalachian Mountains shows male genitalic features somewhat different from those in the population extending from central Texas to northern Mexico (Mockford & García Aldrete, 2010). Within the larger species groups of Lachesilla, other North American speciational events will probably be revealed when relationships are better understood.
In the Family Philotarsidae, Philotarsus californicus and P. kwakiutl are, with little doubt, sister species. The former, in California, is replaced by the latter further north along the coast and in adjacent mountains.
In the Family Myopsocidae, investigation at the alpha-taxonomic level of the genus Lichenomima is still in an early stage. Little can be said about speciation in the North American representatives of this group except to note that some differentiation must have occurred in southeastern (and southwestern?) United States.
In the Family Psocidae, the species of the genus Camelopsocus probably speciated within the study area. Here, climate and, perhaps, elevation, probably played roles in the speciation events. Two species in southern California, C. bactrianus and C. hiemalis, and one species in southern Arizona, C. tucsonensis, are winter species, maturing from late December to February. The other two named species, C. monticolus and C. similis are summer species found at somewhat higher altitudes (see Mockford, 1965Mockford, , 1984b. Mockford (1971) reviewed parthenogenesis in psocids through the literature of 1969. The overall conclusions have changed little. Parthenogenesis in psocids is always thelytoky (female-producing), and, in general, it is obligate within the strain or species in which it occurs. Betz (1983) found four morphologically distinguishable forms of Trichadenotecnum alexanderae. Three of these were obligatorily thelytokous forms and would not mate with males of the sexual fourth. The latter, which proved to represent the type of T. alexanderae, was capable of extremely limited facultative thelytoky. He named each of the thelytokous forms as a species and concluded that each was derived from a sexual ancestor. The distributions of these species overlap broadly in eastern United States. Schmidt (1992) confirmed Betz's (1983) findings concerning morphology and reproductive type, and determined the karyotype for each of the morphospecies. One of the species, T. castum, proved to be triploid, for which a hybrid origin was suggested.

Speciation involving thelytokous parthenogenesis
Several other examples of speciation in North America involve production of a thelytokous species, morphologically distinct from a closely related sexual species. In the Family Philotarsidae, Aaroniella badonneli and A. maculosa form a closely related species pair in which the former is thelytokous and the latter is sexual. In this case, the range of the sexual www.intechopen.com species is more northerly than that of the thelytokous one, although the two species overlap in distribution (see also Mockford, 1979, in which A. badonneli is discussed under the synonym A. eertmoedi).
In the Family Peripsocidae, the Peripsocus alboguttatus species complex consists of three sexual species and one thelytokous species. The latter, P. maculosus, together with its close sexual congener, P. madescens, occurs widely throughout eastern United States and southern Canada, both species primarily inhabiting conifers. This case seems to require further investigation.
It has long been known that infection with certain bacteria, primarily of the genus Wolbachia, can disable sexual reproduction in various insects, so that the infected line carries on by thelytoky. Shreve et al. (2011) reviewed this area relating to Psocoptera and noted no known cases and little likelihood of such a phenomenon in this group. Investigations on Liposcelis bostrychophila, a common cosmopolitan stored-product pest, have shown the presence of a Rickettsia-type bacterium. The domestic form of this species is obligatorily thelytokous, and Perotti et al. (2006) noted that a Rickettsia infection in this species is obligate for egg production. Behar et al. (in press) have shown that this Rickettsia, identified as R. felis, is present in both sexual and parthenogenetic strains of L. bostrychophila and so does not affect the type of reproduction. A Wolbachia infection has been found in a thelytokous strain of Echmepteryx hageni (K. Johnson, pers. comm.), but it is not known to be the causative agent of the thelytoky. It is obvious that much more investigation needs to be carried out in this field.

Endemic taxa above the species level
The genus Speleketor of the Family Prionoglarididae appears to be endemic to North America, with three species, all occurring in southwestern United States: S. irwini and S. pictus in southern California, and S. flocki in Arizona and Nevada (see Mockford, 1984a). The latter species is a partial cave inhabitant. Speleketor irwini lives in the skirts of dead leaves on native stands of the palm, Washingtonia filifera, in canyons. Speleketor pictus is known from a single specimen collected by black light, so its habitat remains unknown. It is likely that additional species will be found, and a nymph probably representing an additional species was collected in a cave near Laguna de Sánchez, Nuevo León State, Mexico. The closest relatives of this genus are the sensitibilline psocids (genera Sensitibilla and Afrotrogla) from Namibia and South Africa (see Lienhard 2007. The entire Family Prionoglarididae appear to be ancient, and Yoshizawa et al. (2006) suggest that they may be Pangaean relics.
In the Family Sphaeropsocidae, two genera are endemic to North America: Prosphaeropsocus and Troglosphaeropsocus (Mockford, 2009). The former genus, with two known species, is found in ground litter on coastal hills in central California. The latter, represented by a single male, is from a cave in northern Arizona. Mockford (2009) presented a strong argument for sister-taxa relationship of the genera Troglosphaeropsocus and Badonnelia. This would suggest great age for the resulting taxon, as Badonnelia is known from a north-Holarctic, primarily domestic species, and four species from southern Chile (Badonnel, 1963(Badonnel, , 1967(Badonnel, , 1972. This presumably extinct stem taxon and its offspring genera may represent another Pangaean relic.
In the Family Psocidae, the genus Camelopsocus is nearly endemic to North America, although the ranges of two of the species extend into southern Mexico. As noted above, this genus consists currently of two summer-active species widely distributed in the mountains of western United States and Mexico, and three winter-active species in deserts of southern Arizona and coastal and near-coastal scrub in southern California. This suggests late www.intechopen.com Miocene-Pliocene adaptation of a form derived from a mountain-inhabiting ancestor to lowland areas with summer climate becoming gradually unfavorable, followed by further geographic speciation in both lowland and upland taxa. Camelopsocus has no close relatives in North America and appears to be closest to the Palaearctic genus Oreopsocus, as represented by the Egyptian species, O. buholzeri Lienhard.

Human effects
Although there are no documented cases, it is possible that a low level of extinction of psocid species has been brought about by human activities, such as extensive deforestation in the East and destruction of the tall grass prairie in the Midwest. An undescribed species of Psocus is known from only two females collected on tamarack (Larix laricina) in a bog in central Wisconsin. Is this species going extinct due to human destruction of its habitat, or will further collecting effort find it in some numbers? We do not know at present. Valenzuela graminis is a species of tall grass prairie remnants in central Illinois. It is persistent in these prairie remnants, and it tends to find its way into restored prairies, despite the fact that females of this species are often short-winged. It is clearly not in danger of extinction.
A glance through Table I shows that numerous species have had the opportunity to expand their ranges through the agency of human commerce. This may be viewed as a form of insurance against extinction.

Status of knowledge and needed research
Distributions of most North American psocid species remain poorly known. The known distributions still tend to reflect where specialists have lived rather than the true distributions of species. Much more collecting needs to be done, especially in the northern tier of US states and southern Canada, along the Atlantic and Pacific coasts, the northern and western coasts of the Gulf of Mexico, and throughout the Southwest. Although funding is difficult to find for studies on Psocoptera, it is not impossible, and careers filled with new discoveries are available.