Psocidae

Introduction

The family Psocidae is the largest family of Psocodea, containing over 60 genera and over 900 described species worldwide.  These are small to large-sized bark lice (2-8 mm) with diverse morphology.  Most species live on bark, but a few are ground dwelling.  Psocidae includes the largest species of bark louse, in the South American genus Thyrsophorus. 

Psocidae contains three subfamilies: Psocinae and Amphigerontiinae (distributed worldwide), and Thyrsophorinae (Central and South America and recently found in Vietnam).

Characteristics

Synapomorphies:

• Presence of an articulation between hypandrium and clunium.
• Presence of the posterior lobe of the external valve of the gonapophyses.

Head:

• Antennae 13-segmented.
• Tarsi 2-segmented; tarsal claws toothed or not.

Wings:

• Cubital loop always joined to M for a distance in the forewing.
• M in forewing with three branches.
• Forewings nearly always glabrous; setae sparse and small if present.
• Aerola postica joined to the media by fusion of CuAI with the media.
• Hindwing nearly always glabrous except for few setae between R2,3 and R4,5.

Click on an image to view larger version & data in a new window

Forewing of Ptycta conforma. Cubital loop and areola postica joined to M is typical of the family Psocidae.
The fusion of veins Rs,M distinguishes the genus Ptycta the sister genus Copostigma.

Male:

• Paraprocts of male with strongly developed clasper-like processes
• Male hypandrium is ornamented variety of forms:  teeth, apophyses, hooks, spines, grooves, ridges and tubercles – symmetrical or not.
• Phallosome usually fairly simple structure closed before and behind, with minimal scleritosation for penial bulb.
• Males of Amphigerontiinae with heavily sclerotised anterior abdomen.

Female:

• Gonapophyses are complete and well developed.
• Ventral valve is pointed.
• Dorsal valve broader than the ventral valve, usually ‘fleshy’ in appearance and apically pointed or rounded.
• External valve is large, well developed and setose.
• Eggs laid single or in groups, covered with encrustation and occasionally, also with silk.

Psocidae Monophyly

The monophyly of Psocidae is supported by both molecular and morphological data. In a molecular analysis that included three Psocinae genera (Loesnia, Metylophorus, and Trichadenotecnum) and one genus of Amphigerontiinae (Blastopsocus) with a data set that combined 18S rDNA, and 12S, 16S, COI rDNA, Johnson and Mockford (2003) found Psocidae to be monophyletic. (The subfamily Thyrsophorinae has not been included in molecular analyses.) Morphological data support the monophyly of Psocidae based on the presence of an articulation between hypandrium and clunium and the presence of the posterior lobe of the external valve of the gonapophyses (Yoshizawa, 2002).

Discussion of Phylogenetic Relationships

Although the phylogenetic relationships within Psocidae have not been studied extensively, 18S rDNA strongly supports the monophyly of Amphigerontinae (based on three genera: Amphigerontia, Blaste, and Blastopsocus). However, Amphigerontinae is embedded within the Psocinae, suggesting paraphyly of Psocinae (Johnson et al. 2004). There is no morphological evidence for the monophyly of Psocinae (Yoshizawa, pers. comm.).

References

Johnson, K. P. & E. L. Mockford. 2003. Molecular systematics of Psocomorpha (Psocoptera). Systematic Entomology 28: 409-40.

Johnson, K. P., K. Yoshizawa, and V.S. Smith. 2004. Multiple origins of parasitism in lice. Proceedings of the Royal Society of London. B. 271: 1771?1776.

Lienhard, C. and C. N Smithers. 2002. Psocoptera (Insecta) World Catalogue and Bibliography. Mus?um d'Histoire Naturelle, Geneva, Switzerland.

Mockford, E. L. 1993. North American Psocoptera (Insecta). Gainesville, Florida: Sandhill Crane Press.

Smithers, C. N. 1996. Psocoptera. Pp. 1-80, 363-372 (Index) in Wells A. (ed.) Zoological Catalogue of Australia. Vol. 26. Psocoptera, Phthiraptera, Thysanoptera. Melbourne: CSIRO Publishing, Australia.

Yoshizawa, K. 2002. Phylogeny and higher classification of suborder Psocomorpha (Insecta: Psocodea:'Psocoptera'). Zoological Journal of the Linnean Society 136: 371-400.

Information on the Internet

• Psoco Net: The Psocidologists' Home Page. The latest information on Psocoptera taxonomy and reserchers in the Psocoptera community, maintained by Dr. Kazunori Yoshizawa, Hokkaido University, Sapporo, Japan.
• Discover Life: Psocoptera Page
• Dr. Charles Lienhard. Psocid expert at the Natural History Museum, Geneva, Switzerland.
• Dr. Edward Mockford. Expert on Psocids of North America and beyond, Illinois State University.
• Dr. Kevin Johnson. Expert on molecular systematics of Psocids and parasitic lice, Illinois Natural History Survey.
• Emilie Bess. Research on Psocids of Hawaii and elsewhere, University of Illinois.