Acarus siro, male
Project Description.
This project includes a plan for monographic research, computerized data generation and access, and training involving mites of the infraorder Astigmata, a large, monophyletic group of considerable interest to agriculture, human and veterinary medicine, ecology and evolutionary biology. The Astigmata comprises some 75 families and 850 genera of mites whose ancestral ecology and ontogeny involve exploitation of temporary habitat patches and the use of phoresy on insect or vertebrate carriers to effect dispersal (OConnor, 1982a). The middle instar or deutonymph is highly modified as the dispersing stage, and its morphology is quite unlike the preceding or subsequent life stages. This dimorphic life cycle has complicated our understanding of the systematics of the Astigmata because taxa are commonly described either from the adults collected from their preferred substrate (fungi, dung, carrion, insect or vertebrate nests [including synanthropic habitats], tree holes or other phytotelmata, cortical and subcortical spaces, etc.) or from deutonymphs collected from insect or vertebrate hosts Only rarely are species known from both morphological phases. Several lineages of astigmatid mites, including one large lineage comprising almost half of the known diversity, have become permanent parasites of arthropods, birds or mammals, and have eliminated the specialized deutonymphal instar from the life cycle. I have previously reviewed the ecological associations of astigmatid mites (OConnor, 1982a) and their phoretic associations with insects and vertebrates (Houck & OConnor, 1991) .
In this current project, we are monographing the genera of the large astigmatid family Acaridae. This family is among the most important groups of mites for several reasons. The Acaridae contains the most abundant and economically important species of mites inhabiting stored food and root crops, inflicting millions of dollars in damage annually (Hughes, 1976) . It is telling that one of these species is Acarus siro, the very first mite named by Linnaeus. This species and many related taxa in this family are also of considerable interest to human and veterinary medicine in that the fauna of stored products also occurs in house dust. Many Acaridae, notably Tyrophagus putrescentiae and related species, are important members of the house dust ecosystem, causing dermatitis and respiratory allergy in humans (Fain, Guérin & Hart, 1990) . Such "stored product mites" also inflict losses in animal husbandry by contaminating feed and causing skin lesions and digestive ulcers in domestic stock.
In addition to their direct economic importance, acarid mites are of considerable interest to basic evolutionary biology and ecology. Many acarid mites exhibit specific associations with their insect carriers, most notably among the Coleoptera and Hymenoptera. Many acarid genera are strictly associated with particular host taxa such as Horstia with the bee genus Xylocopa, Naiadacarus with the fly family Syrphidae, and Passaloglyphus with the beetle family Passalidae. Such systems provide good models for coevolutionary studies and have been the focus of some of my own work in this area (OConnor, 1984; 1988) . In the field of ecology, astigmatid mites in general and the Acaridae in particular are excellent organisms for the study of dispersed metapopulations. Existing in isolated habitat patches and dependent upon insect carriers for dispersal, acarid mites provide ideal systems for testing theoretical models in this currently very active area of ecological research. The Acaridae also provides an interesting evolutionary perspective on ecological shifts. Using the methods of historical ecology developed by D.R. Brooks and reviewed in Brooks & McLennan (1991) , I have hypothesized a series of ecological shifts which occurred during the evolution of the family. Early derivative groups, like most close outgroups, are associated primarily with the nests of vertebrates, often using fleas as dispersal agents. A shift from this habitat type to the nests of insects, especially solitary then social Hymenoptera, then Isoptera, was followed by a loss of specialization and the ability to occupy discrete patches of decaying organic matter in the edaphic and cortical habitats frequented by those insects. Secondary habitat specialization was then followed by new obligate associations with scarab beetles in dung and wood, occupation of confined aquatic habitats (phytotelmata), and even the evolution of permanent parasitism on terrestrial decapod crustaceans. This working hypothesis, however, was based on preliminary phylogenetic analysis of the fewer than one-third of nominal genera available to me at that time (OConnor, 1981; 1982a) .
I have hypothesized the Acaridae to form a monophyletic group based upon morphological synapomorphies (OConnor, 1981; 1982b) and have rediagnosed the family (OConnor, 1982b). I have hypothesized that the Acaridae, along with the small families Glycacaridae, Suidasiidae and Lardoglyphidae, forms a larger, monophyletic superfamily Acaroidea (OConnor, 1981; 1982b), and have more recently included the small family Gaudiellidae in this lineage (OConnor, 1992). The family currently contains 89 genera plus 21 previously recognized synonyms, and about 375 nominally valid species (excluding synonyms). These genera are listed in the Checklist of Acarid Genera accompanying this page.
The Acaridae was last revised by Zakhvatkin (1941) for the fauna of the former Soviet Union. Zakhvatkin included 24 genera in the Acaridae (his Tyroglyphidae) and also discussed four acarid genera he incorrectly placed elsewhere. Nesbitt (1945) attempted a worldwide generic revision, but unaware of Zakhvatkin's work, included only 11 genera including one now excluded from the family. Authors of the 66 genera named since Zakhvatkin's work have relied upon his classification which divided the family into two subfamilies, a monophyletic Rhizoglyphinae and a paraphyletic Acarinae. Subsequent authors proposed monogeneric higher categories for unusual species without regard to phylogenetic relationships. There are presently 15 available family group names whose type genera are in this family.
Two basic problems have confounded the systematics of the Acaridae. The dimorphic life-cycle typical of non-parasitic astigmatid mites complicates our knowledge of the known fauna. Of the 90 potentially valid named genera, only 25 contain at least one species known from both adult and deutonymphal stages. Twenty-four genera are known only from adult morphology, and 41 are known only from the deutonymph. In an unfortunately large number of cases, original descriptions of either stage are inadequate for species recognition, species were based upon small series, and/or little or no information was given on detailed characters such as leg & body setation. Revisionary work has been hampered by inaccessability of specimens from major studies.
The second problem reflects the generally poor knowledge of this fauna and the geographic bias of prior workers. The Acaridae is a cosmopolitan family, but most taxa have been described from the holarctic region; very few taxa are known from tropical areas or anywhere in the southern hemisphere. The most active workers in the last 30 years, the Belgian Alex Fain and the Hungarian Sandor Mahunka, were largely dependent upon others to provide material from outside Europe. Some examples provide evidence for our poor general knowledge of the diversity of this family and particularly the diversity outside the holarctic region. I have reported on the acarid fauna obtained during one week of sampling in a Michigan boreal forest habitat (OConnor, 1991) . Of 26 species collected, only four were previously described, two of which require new generic combinations. In two weeks of sampling in tropical forest habitats in Costa Rica in 1989, I obtained a large number of species, only one of which was previously named. Prior published work on the Neotropical fauna is largely limited to Mahunka's papers on Carl Rettenmeyer's army ant associates (Mahunka, 1978; 1979b) . Likewise, the known fauna of Africa is largely limited to the work of Mahunka (e.g. 1973, 1979a) . These two and other papers in this series are limited to descriptions of largely unassociated deutonymphs from insect traps. Insect hosts and/or habitat associations are known for a very small number of African species. In Australia, only 25 species of Acaridae are known, of which 16 are cosmopolitan human associates, leaving only 9 potentially native species, the majority of which are very poorly described (Halliday, pers. comm. 1994).
The above mentioned problems dictate a strategy with two foci: detailed study of preivously described taxa, and collection and description of new material, particularly in poorly collected regions. Because of the large size of this family, we are focusing our monographic research at the generic level. The main product of this study will be a monograph of the genera of the Acaridae with associated phylogenetic and historical-ecological/coevolutionary hypotheses. A key for identification of all genera of the Acaridae will also be developed. To date, a key has been developed for genera known to occur in North America, however, this key is useful for most genera in the Holarctic region.
This study of the Acaridae will yield ancillary results of several types. Field studies will provide ecological information on microhabitat associations and insect hosts. New collections from the dispersed microhabitats favored by acarid mites will also yield material of other taxa occurring in these communities. Field studies on Acaridae will yield specimens of several other groups which are not normally collected using general habitat sampling strategies. Our work will also stimulate further work in ontogenetic development. Reared series of acarid mites can yield information on developmental patterns potentially useful for systematics as discussed by Klompen & OConnor (1989). Likewise, studies on certain acarid lineages with tight host associations will yield information on coevolutionary patterns and processes (OConnor, 1984; 1988) .
References
Brooks, D. R. & D. A. McLennan, 1991. Phylogeny, Ecology and Behavior: a Research Program in Comparative Biology. University of Chicago Press, Chicago, 434pp. .
Fain, A., B. Guerin & B.J. Hart, 1991. Mites and Allergic Disease. Allerbio, Varennes en Argonne, France, 190pp.
Houck, M.A. and B.M. OConnor 1991. Ecological and evolutionary significance of phoresy in the Astigmata (Acari). Annual Review of Entomology 36: 611-636.
Hughes, A. M. 1976. The Mites of Stored Food and Houses, 2nd ed.. Ministry of Agriculture, Fisheries and Food, Technical Bulletin #9. Her Magesty's Stationery Office, London. 400 pp.
Klompen, J.S.H. and B.M. OConnor 1989. Ontogenetic patterns and phylogenetic analysis in Acari. in Andre, H.M. & J.-Cl. Lions (eds.) The concept of stase and the ontogeny of arthropods. AGAR Publishers, Wavre, Belgium. pp. 91-103.
Mahunka, S. 1973. Auf Insekten lebende Milben (Acari: Acarida, Tarsonemida) aus Afrika II. Acta Zoologica Academiae Scientiarum Hungaricae. 19: 289-337.
Mahunka, S. 1979a. Auf Insekten lebende Milben aus Afrika VI. (Acari: Acarida, Tarsonemida). Acta Zoologica Academiae Scientiarum Hungaricae. 25: 127-157.
Mahunka, S. 1978. The examination of myrmecophilous Acaroidea mites based on the investigations of Dr. C. W. Rettenmeyer (Acari: Acaroidea) I. Folia Entomologica Hungarica (ser. nov.). 31: 135-166.
Mahunka, S. 1979b. The examination of myrmecophilous Acaroidea mites based on the investigations of Dr. C. W. Rettenmeyer (Acari: Acaroidea) II. Acta Zoologica Academiae Scientarum Hungaricae 25: 311-342.
Nesbitt, H.H.J. 1945. A revision of the family Acaridae (Tyroglyphidae), order Acari, based on comparative morphological studies. Part I. Historical, morphological, and general taxonomic studies. Canadian Journal of Research, series D. 23: 139-188.
OConnor, B.M. 1981. A systematic revision of the family group taxa in the non-psoroptidid Astigmata. Ph.D. Thesis. Cornell University. 594 pp.
OConnor, B.M. 1982. Evolutionary ecology of astigmatid mites. Annual Review of Entomology 27: 385-409.
OConnor, B.M. 1982. Acari: Astigmata. in Parker, S. (ed.), Synopsis and Classification of Living Organisms, Vol. 2. McGraw-Hill, New York. pp. 146-169.
OConnor, B.M. 1984. Coevolutionary patterns between astigmatid mites and primates. in Griffiths, D.A. and C.E. Bowman (eds.), Acarology VI, vol. 1. Ellis Horwood, Ltd., Chichester. pp. 186-95.
OConnor, B.M. 1988. Coevolution in Astigmatid mite-bee associations. in Needham, G.R., R.E. Page, Jr, M. Delfinado-Baker & C. Bowman (eds.) Africanized honey bees and bee mites. Ellis-Horwood, Ltd. Chichester, England. pp. 339-346.
OConnor, B.M. 1991. A preliminary report on the arthropod-associated astigmatid mites (Acari: Acariformes) of the Huron Mountains of Northern Michigan. Michigan Academician 24: 307-320.
OConnor, B.M. 1992. Ontogeny and systematics of the genus Cerophagus Oudemans (Acari: Gaudiellidae), mites associated with bumblebees. Great Lakes Entomologist 25: 173-189.
Zakhvatkin, A.A. 1941. Tyroglyphoidea (Acari). Fauna SSSR, Arachnoidea, vol VI, no. 1. English Translation by A. Ratcliff and A.M. Hughes (1959), A.I.B.S. Washington, D.C. 573 pp.
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