Parasitengona

Introduction

The Cohort Parasitengona comprises 6 superfamilies of terrestrial prostigmatan mites and 9 superfamilies of aquatic mites (this group being termed the Hydracarina or water mites) for a total of about 60 families. There are about 7000 named species, 5000 of which belong to the Hydracarina (Welbourn 1991). Many of the named terrestrial species belong to the medically important Trombiculoidea, a group that contains the chiggers (also known as scrub itch mites).

Characteristics

The major uniting characteristic of the Parasitengona is their complex life-cycle, consisting of a parasitic larva, two inactive pupa-like stages that represent the protonymph and tritonymph, and active predatory deutonymphal and adult stages.

Life Cycle and Ecology

Parasitengone mites share a common life cycle that is complex ontogenetically and ecologically (Krantz 1978). They are termed protelean parasites because larvae are parasitic while deutonymphs and adults are predatory. Protonymphs and tritonymphs are inactive, pupa-like stages called calyptostases. Most species of parasitengones parasitize arthropods, but the Trombiculidae, Leeuwenhoekiidae, and an aberrant genus of water mites (Thermacarus) parasitize vertebrates. Amphibians, reptiles, birds and mammals are all subject to attack from these larvae. Trombiculids and leeuwenhoekiids are familiarly known as chiggers or scrub itch mites because of the itchy welts they leave after feeding. They can also transmit parasitic diseases (e.g. scrub typhus), and are thus considered medically important arthropods. Adult parasitengones feed on insect eggs, larvae and pupae as well as other small arthropods. Next to ticks, they are the largest of all mites and can reach body lengths of more than 1 cm. Adults are typically bright red and conspicuous, which together with their often furry bodies has resulted in their common name 'velvet mites'.

Discussion of Phylogenetic Relationships

Welbourn (1991) proposed the illustrated hypothesis of relationships based on a cladistic analysis of 51 genera, using primarily morphological characters of larvae. The relationship between the Hydracarina and the other parasitengones isn't clear, and some authorities consider the water mites (Hydracarina) to be the sister group to the rest of the Parasitengona (Smith & Cook 1991). This hypothesis implies that terrestrial parasitengones are derived from aquatic ones.

Other Names for Parasitengona

• Velvet mites, chiggers, water mites

References

Krantz, G.W. 1978. A manual of acarology, 2nd ed. Oregon State University Book Stores, Corvallis.

Smith, I.M. and D.R. Cook. 1991. Water mites. pp. 523-592 in: J.H. Thorp and A.P. Covich (eds.) Ecology and classification of North American freshwater invertebrates. Academic Press, San Diego.

Welbourn, W.C. 1991. Phylogenetic studies of the terrestrial Parasitengona. pp. 163-170 in: F. Dusbabek and V. Bukva (eds.) Modern acarology, Vol. 2. Academia, Prague,and SPB Academic Publishing, The Hague.