Systematics and Ecology of Rhizoglyphine Acaridae

Kimiko Okabe

Dr. Kimiko Okabe

email: kimikook@ffpri-kys.affrc.go.jp


1. Schwiebea morphometrics. Tagami (1995) reported collecting a species of Schwiebea from swimming pools in Japan. Okabe cultured this mite and found it to belong to the "barbei" group as diagnosed by Fain (1988). Most species in this group have been described from small series of female specimens, with species differences being primarily in the form of the female spermatheca and relative lengths of the dorsal opisthosomal setae. We have reared colonies of the "pool mite" in the laboratory, and have obtained series of specimens of "barbei-group" mites from other habitats in North America. Rearing "pool mites" on various food substrates has allowed us to determine the effect of nutrition on body size and setal length. Using charcters used by prior workers to distinguish species, we have conducted discriminant function analyses and principal components analyses on 6 populations of mites and have examined type specimens of several nominal species to determine if individuals from different populations/nominal species can be differentiated morphologically. Our preliminary results suggest that morphometric characteristics are highly variable within populations, particularly those reared on different food substrates. Spermathecal morphology also varies much more within a population reared from a single female than has been described across several nominal species. We conclude that most currently recognized species in the "barbei-group" should be synonymized with the oldest available name, Schwiebea elongata (Banks).

2. Ontogeny of Schwiebea elongata. In collaboration with Dr. K. Kurosa of Japan, we are preparing a redescription of the full ontogeny of Schwiebea elongata from cultures originating in the Japanese swimming pool. This redescription will include the first description of the deutonymph and male.

3. Parthenogenesis in Schwiebea elongata. Based on laboratory cultures, Okabe has observed that S. elongata is parthenogenetic, a rare phenomenon in the Acaridae. This may explain why the majority of species in the genus are known from females only. Some lab reared populations do produce males, and Okabe has been able to modify the population sex ratio through selection. There is, however, no evidence that fertilization takes place, and all females are capable of producing offspring without mating. A test for Wohlbachia parasitism was negative, indicating that thelytoky in this species is an inherent trait.

Schwiebea elongata female with enlargement of spermatheca showing characteristic "cellular" structure.

4. Ontogeny in Passaloglyphus. The genus Passaloglyphus is known from two species based upon deutonymphs phoretic on passalid beetles in Brazil and Cameroun, respectively. OConnor and Ochoa collected live deutonymphs belonging to this genus from Passalus punctiger in Costa Rica, and Okabe was able to establish a colony in the laboratory. In this project, we will describe the full ontogeny of this species, including the previously unknown adult morphology.

Passaloglyphus sp. male and deutonymph ex Passalus punctiger. Note enlarged anterior legs of adult and reduction of para-anal suckers of male. Deutonymph shows characteristic transverse row of conoidal setae on attachment organ.

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