Astigmatina (Astigmata) Hypopi

Superorder Acariformes

  Order Sarcoptiformes

 Suborder Oribatida

   Supercohort Desmonomatides

 Cohort Astigmata - hypopi (heteromorphic deutonymphs, hypopodes)

  

Common names: hypopus (hypopi), hypopode

 

Probability of Encounter: high

 

Quarantine importance: Many Astigmatina of quarantine importance have a specialized dispersal stage, the heteromorphic deutonymph, that lacks functional mouthparts, has a closed gut and reduced capitulum, and usually a sucker plate (or pair of claspers) for attaching to an arthropod (or vertebrate); a few are able to enter the pores in vertebrate skin. 

 

Diagnosis.  Beige, pinkish to dark brown; hemispherical to flattened, usually oval in outline, well sclerotized, with distinct sejugal suture.  Prodorsal trichobothria and pteromorphs absent.  Capitulum tubular to button-like, without functional mouthparts; palps reduced to setiform appendages.  Venter usually with well developed sucker plate.

 

Similar taxa.  Heterostigmata (Prostigmata) often attach to arthropods and could be confused with astigmatan hypopi, especially Scutacaridae, but the latter lack the sucker plate and have a well-developed gnathosomal capsule.

 

Ecology & Distribution.  Hypopi (singular hypopus) are deutonymphs that act as special dispersal morphs of some astigmatans.  Because they do not look like other stages, they are called heteromorphic deutonymphs.  Another term used for this stage by some authors is hypopode.

Hypopi usually do not feed and hence have no mouthparts or anal opening.  The capitulum is reduced to a small tubular or button-like structure, often with a few seta-like processes (true setae and the remnants of the palps).  In a few cases, e.g. some endodermal parasites of vertebrates, the hypopi absorb nutrients through their skin.  Most hypopi disperse by attaching to an insect or other arthropod (rarely lizards) using a complex sucker plate near the rear of the venter.  This sucker plate is highly distinctive - if you see it you know that you have some kind of hypopal astigmatan. Formation of the hypopal stage is usually facultative in response to deteriorating environmental conditions.  Most vertebrate parasites and some common stored product astigmatans have completely lost the ability to form hypopi (e.g. species of Tyrophagus).

 

References

Houck, M.A. & B.M. OConnor. 1991. Ecological and evolutionary significance of phoresy in the Astigmata. Annual Review of Entomology 36: 611–636.

Hughes AM.  1976.  The Mites of Stored Food and Houses.  Technical Bulletin 9, Ministry of Agriculture, Fisheries and Food: London

Krantz GW.  1976.  A Manual of Acarology.  OSU Bookstores: Corvallis.