horses and, to some extent, sheep, goats, and dogs. Man is un commonly attacked by adults, but more frequently by larvae and nymphs. H. dromedarii is so intimately associated with camels that it does not occur outside the normal range of these animals. However in parts of Anatolia where camels are now considerably less numerous than heretofore, large numbers of adults have been found on cattle and horses, fewer on sheep and goats (Hoogstraal, ms.). In nature, remote from large concentrations of domestic animals, larvae and nymphs feed on small burrowing mammals and hares, rarely on lizards. Adults venture forth in search of larger hosts. Nymphs appear to be more versatile, depending on local situations, and may infest camels, cattle, and horses in large numbers. Factors inducing the selection of hosts by nymphs are in need of study. In the laboratory, Delpy and Gouchey (1937) fed larvae on hares and calves but this stage rarely engorged on camels or sheep. The same was true for nymphs. Adults attached rapidly to camels and cattle, rarely to sheep. It was often difficult to rear on a calf the F1 generation of a female collected on a camel. Further review of Delpy and Gouchey's report is presented in BIOLOGY below. In Yemen, Southwestern Arabia, numerous larvae and nymphs have been collected from the following hosts (Hoogstraal, ms.): Lepus arabicus arabicus Ehrenberg Lepus arabicus subsp. Rattus rattus rattus Linnaeus (rare) Gerbillus cheesmani maritimus Sanborn and Hoogstraal In Egypt, including Sinai, nymphs have been taken from hedgehogs, hares, rodents, and lizards (identifications based on adults reared from nymphs) (Hoogstraal, ms.). Hemiechinus auritus aegyptius Fischer (common on Paraechinus aethiopicus dorsalis Anderson and De Winton Lepus capensis sinaiticus Ehrenberg (few hosts examined) Gerbillus (Lipodillus) quadrimaculatus Lataste (rare) Gerbillus p. pyramidum Geoffroy (common) Meriones c. crassus Sundevall (common, also in burrows) Acanthodactylus boskianus Daud. (Lizard) (uncommon) According to Pomerantzev (1934) hosts of the immature stages in Armenia include reptiles and wild birds. The fatty sub cutaneous layers of ground squirrels, Citellus sp., used as laboratory hosts (Pospelova Shtrom 1932), may hinder the attach ment and feeding of larval H. dromedarii (= H. yakimowi). In Russia (Pomerantzev 1950), adult hosts are camels, horses, and sheep while nymphs feed in large numbers on cattle and camels. Hosts of adults of the synonymous H. asiaticum are camels, cattle, horses, and sheep; rarely donkeys, goats, domestic and wild pigs, hares and hedgehogs; sometimes man. Nymphs of this latter form occur on hedgehogs, in burrows of large "peschanki" and gophers, while larvae are often on hedgehogs. Both immature stages are found (?together) on hares, gophers, jerbo as, "peschanki", cats and dogs, and single nymphs are found on cattle and sheep (Bogoroditsky and Bernadskaia 1938). BIOLOGY Life Cycle The question of the normal number of hosts of H. dromedarii is moot. Delpy and Gouchey (1937) consider it as a three-host tick that may utilize only two hosts under unfavorable conditions; i.e. great heat, when larvae molt quickly and reattach as nymphs nearby on the same host in order to avoid desiccation. It would appear that normally, on burrowing mammals, this need would not arise since the hosts venture from their relatively cool tunnels only after the sun goes down (deserts are usually cool at night). Alfeev (1951) reared H. dromedarii as a single host tick on rabbits and noted that adults move to new positions shortly after molting and remain unattached to the host for a day or two afterwards. Field observations suggest that this is normally a two host tick, the change in hosts usually occurring after the nymphal adult molt, infrequently after the larval nymphal molt (Hoogstraal, ms.). In Russia the former type appears most common (Pomerantzev 1950). Experimentally, Pospelova Shtrom (1932) bred H. dromedarii (= H. yakimowi) on one, two, or three hosts. For the single host life cycle, she employed the hedgehog. The highly artificial conditions and exceptional hosts utilized in this experiment pre clude additional deductions from the results. During the warm season in Iran, the briefest life cycle ob served by Delpy and Gouchey (1937) was 93 days: During cold weather, 280 or more days were necessary. Two generations a year may occur in nature. Variations in life cycle length are due to external or climatic factors affecting oviposition, hatching, and premolting periods; feeding times are similar at all seasons. These findings are diametrically opposed to those of Pospelova Shtrom (loc. cit.), who concluded, after rearing two generations under different temperature and humidity conditions, that varia tions in the length of different stages depends more on host bodytemperature than on atmospheric differences. The Delpy-Gouchey conclusions are more in line with usual concepts concerning factors affecting tick life cycles. (See page 704) In Egypt, some slight seasonal variation in incidence of adults on camels is noticed (Hoogstraal, ms.). Normal life cycle activity appears to continue the year around, except that it is slower during the winter. For instance, during the summer, nymphs molt to adults from seventeen to 26 days after dropping from the host while in winter this period is extended to from 27 to 48 days. Feeding time for each stage, according to Delpy and Gouchey, is as follows: These authors reported individual females laying from 2000 to 8000 eggs, but Pomerantzev (1950, for the synonymous H. asiaticum) notes as many as 14000 eggs. Males mate with unengorged or with feeding females while on the host. In the absence of males, females either detach pre maturely from the host or remain fixed for an exceptionally long time as long as two months. In the Kazalinski district of Russia (Pomerantzev 1950), adults parasitize domestic animals from April to the end of October, but are most common from May through August while larvae and nymphs attack hedgehogs in July and August. Fe males that become engorged late in autumn undergo a winter diapause and do not oviposit till spring. Ecology Delpy and Gouchey (1937) found H. dromedarii to be very tolerant of low humidity and extremes in temperature (0°C. to 37°C.). Unfed larvae and especially unfed nymphs avoid dry atmosphere more than engorged stages and adults. H. dromedarii is probably the most completely desert-adapted of all ixodid ticks. In remote Siwa Oasis of Egypt, it, together with R. sanguineus, is the only common ixodid tick. Italian and French observers elsewhere in North Africa and Soviet workers in Russia have made similar observations. The camel hyalomma ap pears to be equally at home in all desert situations where ani mals occur, as well as in semi desert and steppe areas. In Yemen and Eritrea, it is also common in mountainous areas to 7000 feet altitude wherever there are people and camels (Hoogstraal, ms.). When traveling over remote parts of the African and Arabian deserts engorged females have been observed desperately crawling on sand. The opportunities for dispersal of H. dromedarii over long camel routes may easily be imagined, but a large number of ticks undoubtedly perish in either the egg or larval stage along these wide and indefinite trails through barren deserts. Blanc, Martin, and Bruneau (1949) report females on camels that had arrived, after a trek of longer than a week, across the Sahara, at Goulimine in southern Morocco from Mauritania, over a thousand kilometers away. In Egypt, similar infestations are found in the Cairo area on camels just arrived from the Sudan (these also bear other Sudanese but not Egyptian species of ticks) and in Siwa Oasis on camels from distant parts of Libya. In Egypt, unfed adults may be taken on the desert of the Mediterranean littoral at any time of the year. Unfed adults either come rushing at any potential host, including man, from under desert shrubs or are collected in rodent burrows before they depart in search of larger hosts. Engorged, ovipositing females may be observed in rodent burrows as well as under des ert shrubs, in camel yards, and under stones. On the littoral desert unfed adults are seen at any time of the day in all sea sons. REMARKS In attempts to determine whether larvae produce an acquired immunity in the hosts, thus preventing subsequent larvae from engorging on the same animal, Brumpt and Chabaud (1947) fed this stage on rabbits with negative results. Differences in size of each stage and sex have been presented by Campana Rouget (1954). A capillary tube arrangement, which has proved successful for the artificial feeding of adults of H. dromedarii for physio logical and disease transmission studies, has been described by Chabaud (1950A). Parasitic wasps (Hymenoptera), Hunterellus hookeri, have been bred from nymphs of H. dromedarii (H. asiaticum) in Russia by Bernadskaia (19398). |