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and thus to form a very efficient seal of the ostium, a necessary

condition for animals so likely to be exposed to desiccation. It is of interest to compare Browning's study with that of thur (in press) on the spiracle of Ixodes 7.

According to Mellanby (1935), the physiological reaction that governs the opening and closing of the spiracular ostium is similar to that of insects. Browning (1954B) appears to accept this conclusion. The physiology of spiracular action has been discussed under Environmental Adaptability above.

Haller's Organ

The structure of haller's organ and its supposed value as a phylogenetic indicator has been discussed by # W. Neumann (1943). Schulze (1941) also described and illustrated haller's organ, which functions as an organ of smell. Incidentally, Zumpt (1949) summarized his studies on the systematic importance of this structure as follows: Research up to now indicates that haller's organ will have to be considered in the future as having a role in tick systematics and should not be overlooked.

Abnormal Development

During examination of about eight thousand laboratory reared specimens of 0. moubata, Robinson (1943A) encountered two examples of partial twinning Of"the posterior area in a third instar nymph and in a fifth instar nymph that subsequently molted to a male and female, each with abnormalities in internal anatomy. These specimens were normally fertile. Another peculiarly humped third instar nymph normally molted to a male that showed suppression of the postanal region. This male failed to copulate although the genital system was well developed and the sperm normal. RobinSOn £5 also noted many abnormalities of the legs during handling of about ten thousand tampans. Most cases were deficiencies due to partial regeneration of a leg damaged in a previous nymphal instar. Two cases of supernumerary segments of legs were also observed and illustrated. In the same batch a nymph that was much more completely twinned posteriorly than previous examples was observed. This specimen molted to a partially twinned female, mated normally, refused to feed, and deposited a small egg batch (not particularly

unusual for unfed females). Some of these eggs developed into normal ticks but most were not delivered into the arms of gene's organ and therefore did not hatch. In the same paper, Robinson reviewed reports of partial twinning in other tick species. Leg anomalies have been reviewed by Campana (1947).

Symbiotes

Tissue cells of many normal insects and ticks harbor living microorganisms that for the most part exert no harmful effects on these cells. In fact, some of them may be distinctly beneficial to the hosts, carrying out their part of a mutually helpful relationship. A Steinhaus (1947) 7

In some respects, the relationships between arachnids and their symbiotes are very similar to those between insects and theirs. Among noteworthy differences, however, appear to be the absence of mycetomes in ticks, though some mites have these structures. Furthermore, most tick symbiotes occur in the malpighian tubules and in the ovaries instead of in the alimentary tract, though this may not be true for certain of the rickettsiae. The two families of ticks are similar with respect to symbiotes; in both the same organs are associated with microorganisms. They differ, however, in the manner of ovarial infection. A Steinhaus

(1947) 7

Intracellular clusters of large masses of typical rickettsiae were discovered in salivary gland acini of O. moubata by Hertig and Wolbach (1924). Intracellular symbiotes were not found in larvae (?nymphs) of O. moubata by Cowdry (1925C, 1926A,1927), though they were demonstrated in Argas persicus and in Otobius megnini. Other extensive reviews of symbiotes in ticks are # of Mudrow (1932) and Jaschke (1933).

In O. moubata, unlike ixodid ticks, symbiotes, probably of a bacterial nature, do not occur in the anterior ends of the malpighian tubes but rather in about one-fifth of the length of the tubes just posterior of the anterior ends. In this, O. moubata differs from A. persicus, in which Jaschke observed intracellular symbiotes in masses as large as five microns in diameter and containing as many as forty individual organisms each.

In O. moubata and other argasids, symbiotes may migrate from the malpighian tubes to the ovaries and developing eggs, thus differing from ixodids in which they directly invade the first sex cells (Mudrow 1932). This worker sought the explanation of symbiotic bacteria in the realm of physiologic relations of nutrition. (See three paragraphs £5.

Argasid symbiotes do not appear to be as pleomorphic as those of ixodids and are usually of the rod or coccus type though they are grouped into apparently gelatinous masses or colonies. Rows or chains of granules or filamentous bundles are not seen in these masses. Tick symbiotes have not been artificially cultivated although Steinhaus attempted to do so with those from

Argas persicus by utilizing fluids and tissues of the chick #: Z-Steinhaus #

With reference to the "bactericidal action" in the guts of insects and A. *sicus and 0- moubate (Duncan 1926), the reader is referred to subsequent findings in the following series of papers on work done with A. persicus: Anigstein, Whitney, and Micks (1950A,B), Whitney, Anigstein and Micks (1950), and Micks, Whitney, and Anigstein (1951). The intestinal tract of bloodengorged ticks exhibited significantly higher antibacterial titer than those that had not been fed. Study of animal blood itself revealed erythrocytic enzymatic hydrolysates showing marked in vitro antibacterial effect over a relatively wide spectrum of most gram-positive and a few gram-negative organisms. The active principle of the hydrolysate appears to be a peptide amino acid complex, called sanguinin, which, as a powerful enzymatic inhibitor, represses the growth of several organisms including streptococci, both in vitro and in vivo.

The role of symbiotes in producing growth-promoting substances in O. moubata (and in bedbugs) has been studied briefly by De Meillon and Goldberg (1947A,B). Feeding nymphal and adult ticks on thiamin-deficient rats resulted in almost doubling the time necessary for completing the tampan's life cycle, increasing the interval between blood meals and molting, and an additional molt before reaching maturity. Normal growth and reproduction, however, follow feeding on riboflavin-deficient rats (De Meillon, Thorp, and Hardy 1947). The purpose of these experiments, fol

lowing work by Brecher and Wigglesworth (1944) on the blood-sucking hemipteron Rhodinus prolixus, was to test the ability of symbiotes in the tick to produce growth-promoting vitamins in the absence of these substances in host blood. Thiamin, it appears, cannot be manufactured by symbiotes under these conditions but riboflavin can be produced in sufficient quantities for normal development and reproduction. Incidentally, it was noticed that the severity of host skin reaction to bites of O. moubata is greater in animals that are deficient in thiamin than it is in normal rats. In the former, an extensive hemorrhage develops at the site of each bite (De Meillon and Goldberg 1947A,B, De Meillon 1949).

Laboratory Rearing Methods

This subject has been discussed in more or less detail by all students of the life cycle, mentioned above. Methods for rearing Q. moubata, care of hosts, caging, precautions, host diet and handling, etc., have been presented by Harvey (1947).

Artificial Feeding

A capillary tube method for the artificial feeding of 0. moubata and other ticks for studies of disease transmission and physiology has been developed by Chabaud (1950A).

Prevention and Control?
Prevention
Travellers in infested areas should be cautious especially

in choosing sleeping and sitting sites. Indigenous habitations whenever possible should be avoided for sleeping, and care should

*Although it is not the policy of this study to deal with control and prevention subjects because these are more logically included in a separate report now being prepared, an exception is made in the case of O. moubata. The control and preventive measures required for this species are unique among African ticks, and its biological and host predilections are different from all others. Moreover, it is possibly the only medically important African tick that has little or no veterinary importance.

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