Parthenogenesis in Psocids (Insecta: Psocoptera)

Mockford, Edward

ABSTRACT: Obligate thelytokous parthenogenesis and, more rarely, facultative thelytoky are known to occur in psocids. The former phenomenon is known in 28 species. The latter is known only in two species, both of which have obligatorily thelytokous forms as well as bisexual ones. Attempts to force thelytokous females to mate have been carried out for four nominal species. All have failed. Differences in color or color pattern between the bisexual and thelytokous forms of a nominal species have been observed in two instances. In Echmepteryx hageni this seems to involve divergence where the two forms occur sympatrically but on different habitats. Investigations of geographic distribution of bisexual and thelytokous forms of a nominal species show in several cases that the thelytokous forms are much more widespread than the bisexual ones. In eastern United States, bisexual forms tend to occur peripherally and in ecologically unusual areas. The areas of occurrence of bisexual populations may be relictual, and some of them may have been Pleistocene refugia. Most of these areas correspond to areas where coniferous trees now form an important part of the forest.