The Geographical and Ecological Distribution of Arboreal Psocoptera

Annu. Rev. Entomol. 1985.30:175-196. Downloaded from arjournals.annualreviews.org
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176 THORNTON
Ecological Role
FEEDING AND BIOMASS Although usually designated as scavengers or detritivores
when ecological roles are assigned to the various components of
ecosystems, arboreal Psocoptera are in fact grazers, and their pastures are the
microepiphytes (fungi, algae, and lichens) that grow on the bark and. leaves
trees and shrubs and in the litter. Some also take pollen grains. The peculiarities
of psocid mouthparts and the massive clypeal muscles may in the future be
shown to be specifically related to this grazing type of feeding. The ecological
importance of psocopterans in forest ecosystems has until recently been either
neglected or assumed to be small. However, considerable information is now
available on their role in temperate and, to a lesser extent, tropical forest
ecosystems as a major component of the guild of microepiphyte feeders.
In temperate forests the primary productivity contribution of microepiphytes
may be comparable to that of the herb layer (92), and grazing psocids may make
up a significant part of the biomass. Densities of over 4000/m2 on the bark of
larch (Larix decidua), equivalent to over 6000/m2 of land surface, have been
recorded in Yorkshire, England, during late summer (16). The peak biomas s
two species of Mesopsocus was about 1.2g/m2 of ~ bark surface, or about 2g/m
of ground surface. This is comparable to the biomass of various kinds of big
game animals such as antelopes feeding on grasslands, and at peak times the
grazing of microepiphytes by psocids can be very intense.
In the tropics, psocid densities are much lower. However, in an altitudinal
transect of canopy arthropods from sea level to 2400 m subtropical Hawaii
(26), psocids were frequent and abundant on the two dominant trees examined
and outnumbered all other taxa combined at mid and high elevations. Clearly,
psocid populations can be important primary consumers and saprophages.
PREDATION " In Britain a polyphagous mite of the genus Anystis is frequently
recorded as a predator of psocids. In Yorkshire it may be responsible for much
of the high mortality of first instar larvae of Philotarsus picicornis besides
causing significant egg mortality in Mesopsocus species (23).
In southern England, spiders, mites, opilionids, neuropteran larvae, anthocorids,
earwigs, and carabids have been reported to attack egg batches of
foliicolous psocids. Some 26 predators have been recorded (15, 99): the most
important are spiders (by far), mites, opilionids, neuropteran larvae, and
coccinellid beetle. Of the three major groups of epiphyte herbivore:s on larch,
the majority of predators select Psocoptera and Homoptera rather than the
numerically more abundant Collembola.
Ants (Crematogaster sp.) in Brazil have been seen at night attacking and
carrying off archipsocids that live under large communal sheet-webs. In Florida
archipsocids are preyed upon by Argentine ants and reduviid bugs.