Feeding Habits in the Genus Balaustium (Acarina, Erythraeidae), with Special Reference to Attacks on Man

Abstract

Although mentioned frequently in acarological literature, the genus Balaustium is poorly known. In recent years authenticated cases of attacks on man have shown the need for accurate information on feeding habits in this genus. Observations by the writer and others show that species of Balaustium have very generalized feeding habits. Food sources include pollen, leaf tissues, and insects. Man is also attacked, probably in situations which bring numbers of Balaustium into incidental contact with potential human victims. Symptoms of attack vary widely, probably as a result of individual susceptibility, or possibly with the species of Balaustium involved. Information on the latter point is not available at present because of the inadequate state of our knowledge of the systematics of this genus. The cosmopolitan genus Balaustium was first described by Von Heyden in 1826, with Trombidium murorum Hermann, 1804, as type species. About 40 or more species have been ascribed to the genus subsequently from most parts of the world, but the descriptions of these have been so brief and the diagnostic characters so little known that it is impossible to say at the present time just how many species are involved. Likewise, very little has been written about their biology, especially about their parasitic relationships with other organisms. These mites have a characteristic body form (Figs. 2, 3) and are generally brick-red or brown in color, sometimes with a metallic green sheen. When fully mature they measure between 1.0 and 1.5 mm in length, exclusive of the appendages. The legs are relatively short, with legs I about as long as, or slightly shorter than, the body (Fig. 1) in contrast with many other Erythraeidae in which one or more pairs of legs are markedly longer than the body. They can be differentiated readily from closely related short-legged Erythraeidae by the possession of a single pair of eyes, behind which is a pair of glandular openings Received for publication 15 January 1963. * This study is being supported by a grant (E2533) from the National Institutes of Health, Public Health Service, to the University of California, Riverside. borne on collarlike tubercles. Superficially, these tubercles give the mite the appearance of having two pairs of eyes (Fig. 3). They are absent in the larva but are present in the active nymphs and the adults.' Species of Balaustium are found on a variety of substrates including soil litter of many types, the trunks of trees, the leaves or flowers of plants, and on stone walls and other structures. The adults are often extremely aggressive predators of small insects, including the nymphs of Hemiptera, Thysanoptera, and other orders. It does not appear that they are very specific in the hosts that they select, although information along this line is not adequate to justify any general statements. The writer has seen unusually heavy populations on Artemisia, Ribes, Quercus, and other plants sufficiently numerous and various to indicate that species of Balaustium may become abundant under a variety of environmental conditions. The writer assumes, as did Oudemans, Grandjean, and other workers, that the short-legged Erythraeidae with elevated openings dorsally just posterior to the eyes are congeneric with Trombidium murorum Hermann, 1804. As Grandjean (1947, 327-328) has pointed out this assumption is arbitrary and not capable of demonstration. Nevertheless, the writer feels that this assumption is justifiable on the grounds of probability and in the interest of nomenclatorial stability. Southcott (1961, 540-548) summarized much of the information presently available on the European species.