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BIOLOGY

Life Cycle

Laboratory studies indicate that R. s. simus undergoes a three host type of life cycle.

Under experimental conditions, Theiler (unpublished), Lewis (1932A), and Lounsbury (1905) have found the life cycle periods to be as follows:

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Note: Theiler rearings at 24°C. to 26°C. and approximately 80% R.H.

Hares were used as hosts for all stages in Lewis' experiments, though not with great success. The ease with which these observations could be repeated using normal hosts and normal conditions of temperature and humidity found in rodent burrows suggests an interesting study for collecting comparative data.

Field observations indicate that both immature stages feed on nest inhabiting rodents. The nymphal adult molt occurs in the same nest, and adults remain in the nest for some time before seeking larger hosts. As discussed below, a considerable amount

*2 months in winter.

of additional field study is required to answer many questions concerning the life cycle of R. s. simus. This tick and H. leachii are the only ubiquitous African species that in their immature and adult stages, respectively, feed first on nestinhabiting rodents and then on larger animals. More rigid field observations, besides being a most pleasurable occupa tion, should be easily accomplished.

In the following paragraph the question of where the female oviposits is raised. In this connection, Howard's (19098) ob servation of an unengorged male and female of R. simus (- R. ecinctus) mating on the leaf of an Acacia thorn tree on the Zambesi River is of special interest (although the possibility of misidentification of these specimens must be considered). Almost invariably, rhipicephalid ticks mate on the host, as do most other ixodids. Howard's note indicates the necessity of further research to determine whether R. s. simus possesses a unique type of mating and egg laying, and, if so, whether this is a constant or an exceptional phenomenon, and whether it is associated with an ability of larvae to seek out their preferred habitat and hosts rather than waiting for a passing rodent.

Mating observed by J. B. Walker (correspondence) in Kenya has been of the ordinary rhipicephalid type, on the host. Walker also says that engorged females that have already dropped from the host will mate with males that have been feeding on the same host and then removed and placed with these females. This might be merely a mating act and not initial or essential fertiliza tion (HH), for generally, it appears, female engorgement is not complete or normal unless copulation has been effected.

Ecology

From Roberts (1935) studies in the Nairobi area it appears that the immature stages of R. s. simus prefer slightly subsurface rodent nests rather than deeper nests of the same and of other kinds of rodents. The grass rat, Arvicanthis, is possibly the most important immature stage host. It is not known whether larvae actually seek out the nest and attack the animal there, or whether they attach to a rodent wandering in search of food and are then carried to any nest that their host might be in

habiting. It would be contrary to all previous observations on ixodids to assume that the female selects the situation in which she oviposits, although this possibility must be investigated.

By way of comparison, immature stages of H. leachii in the Nairobi area prefer deeper nests of Mastomys coucha. In the Njoro area of Kenya and in the Sudan, however, we have taken larvae and nymphs of these two ticks species in both shallow and deeper nests.

Arvicanthis nests are usually within a foot of the surface of the ground, but sometimes they are two or three times as deep. The nest is reached by a network of a few or many tun nels, each with a small exit among vegetation. The round nests, composed of lesser or greater amounts of moist grass and leaves, appear to be occupied for several generations. Slight rises, such as borrow heaps, mounds beneath bushes, or pathsides are favorite burrowing sites. These rodents frequently nest and search for food in close association with human activities.

Habitats of some of the chief South African hosts of im mature stages (see HOSTS above) differ widely. Aethomys namaquensis frequents rock crevices and piles of stones while A. chrysophilus is more terrestrial and lives in sheltered bush on the plains, among rocks, or in burrows under bushes or rocks. Otomys lives in holes in the ground or in selfmade shelters in matted vegetation; those in the Karroo construct these shelters from large piles of weeds while others utilize small grass or weed nests in marshes or among rocks. Rhabdomys hides in holes in the ground and its pathways run through dense vegetation. It is evident, therefore, that the usual ecological niches of hosts of immature stages in East Africa differ from those in southern Africa.

In southern Africa, Theiler (unpublished) finds that the glossy tick occurs from the eastern tall grass veld (Port Eliza beth) northwards through subtropical overgreen and deciduous tree and thorn forest into northern Transvaal, Southern Rhodesia, and Mozambique. In these subtropical stretches, the heavy rain fall areas of Natal are comparable with the coastal plains of Kenya, and the dry, warm conditions in Kruger National Park and northern Transvaal are comparable with central Kenya (see next paragraph). Records indicate this tick to be less common west

of the Drakensberg escarpment, but to occur up to 10,000 feet el evation in Basutoland. It is common in Highveld with good annual rains, heavy frost, and snow in winter but seldom recorded from dry Highveld. In the mixed grass veld of the middleveld, with ten to 25 inches of rainfall annually and cold, sharp winter frosts, it is almost entirely absent, though it does occur in southern Transvaal middleveld. It is numerous in the Bankenveld and Limpopo highlands and also in Bushveld regions of Transvaal. In Karroo areas it dies out in areas with less than ten inches of rainfall annually. Records from Southwest Africa are only from the northern, more moist areas. In Southern Rhodesia, it is especially common in eastern and northern areas.

In the hot, more or less humid, coastal lowlands of Kenya, R. s. simus is especially common (Wiley 1953). Dick and Lewis 71947) consider this to be the most abundant and widely distri buted tick in the Kenya coastal lowlands and Wilson (1953) also notes its frequency there in areas where R. pravus and A. gemma are found (cf. pages 681 and 274). In the arid Northern Prov ince of Kenya, the glossy tick is less common than elsewhere in the Colony, but it does occur anywhere under a variety of conditions, whether these be hot and arid, cold, damp high altitudes, or hot, moist coastal lowlands (Wiley 1953). Theiler (1943B), supported by subsequent remarks by Santos Dias, noted that R. s. simus is not only particularly abundant but actually the most ubiquitous tick in some parts of Mozambique.

Study of data for the Somalilands, in the coastal areas just north of Kenya, suggests that R. s. simus is common only under local conditions in these less humid areas. From details published by all investigators concerning the Belgian Congo it would appear that in most parts of the colony this tick is decidedly less common than it is in southern Sudan.

In the Sudan, R. s. simus is common everywhere in the south and at least frequent in southcentral areas. It becomes more localized and uncommon with the approach of semidesert conditions. Many areas in which it occurs have a long, severe dry season but rainfall of twenty to almost fifty inches annually during the wet season. King (1926) noted that although this tick is absent in the desert areas of Northern Province, populations had estab lished themselves there when local conditions of humidity were modified after pump and basin irrigation was introduced.

Altitudinal distribution in Kenya is from sea level to 11,000 feet (Lewis 1932A). Lewis (1931C) considered this species as one relatively little affected by conditions influenced by altitude. In Ruanda Urundi, the glossy tick ranges to about 5600 feet altitude (Schoenaers 1951B). Neumann's (19070,1910B) Tanganyika records include specimens from altitudes up to about 6000 feet. In Arabia this tick is known only from the temperate, watered 3500 foot to 7000 foot range of the Yemen mountains but not from drier and hotter lowlands (Hoogstraal, ms.).

The seasonal cycle of R. s. simus is not well known. During the colder months of the year, Wilson (1946) found no adults in Northern Province, Nyasaland but his collections were mostly from cattle, which are not common hosts there. Engorged females were found during the wet season (Wilson 1950B). In the Sudan newly molted adults were collected in rodent nests during the dry sea son and engorged adults on larger hosts chiefly during the dry season. In Northern Rhodesia, Matthysse (1954) found adults on cattle chiefly during the rainy season, but some also in dry periods. The emergence of adults and the length of time they normally remain in their host's nest at different seasons of the year should be investigated.

On cattle, adults of R. s. simus are usually found on the tail switch, feet, and anus (Theiler 1943, Wilson 1948B, Matthysse 1954). On dogs they feed almost anywhere, as noted by Theiler (1943B) and Wiley (1953). Our Sudan specimens from hippopotamus were all found on the hosts' ears. Neumann's thirty specimens from a Kenyan rhinoceros were taken from the host's inguinal area.

Adults awaiting a host show "a marked predilection for tall grass overhanging paths, but are common everywhere", including in human habitations, where they were associated with boutonneuse fever by Dick and Lewis (1947). They are also found in houses in Somaliland (Drake Brockman 1913B, Veneroni 1928), where they bite children and cause paralysis. The close association between the glossy tick and man is easily understandable. Adults are common on domestic dogs and less frequently, under local conditions, on cattle. The immature stages feed on rodents that frequently nest under vegetation bordering garden plots and cultivated fields, beside roads and paths, near buildings, or in the vicinity of streams where people congregate. Many of these rodent hosts

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