HOSTS

Cattle are the chief host of the blue tick and most papers listed in DISTRIBUTION above refer mainly to this animal and effects of this tick's feeding upon it. Domestic horses and, less frequently, sheep and goats are attacked. Among wild animals, antelopes are important hosts but few others are infested. Wild carnivores are almost never parasitized by this tick. This is a single host tick, therefore hosts of the immature stages are the same as those of adults.

Domestic animals: Cattle (Most papers listed in DISTRIBUTION above). Horses (Howard 1908, A. Theiler 1911, Lewis 1931C, Mettam 1932, Minning 1934). Mules (Howard 1908). Donkeys (Howard 1908, Minning 1934, Sousa Dias 1950, Sudan records above). Sheep (Howard 1908, Schwetz 19270, Mettam 1932, Lewis 1934, Minning 1934, Wilson 1950B, Sousa Dias 1950, Sudan records above). Goats (Howard 1908, Lewis 1931C, Bedford 1932B, Mettam 1932, Cooley 1934, Tendeiro 1948, Wilson 1950B, Sousa Dias 1950, Sudan records above). Pigs (Knuth and du Toit 1921. Sudan records above). Dogs (Lounsbury 1904A reared the blue tick on dogs, but only a few specimens com pleted their life cycle on these animals. Howard 1908, Bedford 1932B, Mettam 1932, Sousa Dias 1950. Bahr el Ghazal specimens in Sudan records above were collected from dogs belonging to Dinka herdsmen; these animals sleep in cattle huts). Camels (King 1926). Water buffalo (Theiler, unpublished).

Man: (Nuttall 1911B, Bedford 1920).

Antelopes: Grant's gazelle (Weber 1948). Sable antelope (Bedford 1932B, Cooley 1934, Jack 1942. Roan antelope (Simpson 1914, Jack 1942). Blue wildebeest (Bedford 1932B). Gnu (Santos Dias 1950B). Hartebeest (Lewis 1934, Santos Dias 1950B, Sudan records above). Nyala (Santos Dias 1950B,1952D). Tiang (Sudan records above). Impala (Bedford 1932B, Gooley 1934, Jack 1942, Meeser 1952, Santos Dias 1952). Reedbuck (Santos Dias 1950B). Bushbuck (Mettam 1932, Lewis 1943, Santos Dias 1950B). Waterbuck (Bedford 1932B). Eland (Lewis 1943. (Lewis 1943. Sudan records above). Sitatunga (Bequaert 1931). Oryx (Minning 1934). Duikers (Mettam 1932, Cooley 1934). Topi (In Miss J. B. Walker's collections from nu merous game animals in Tanganyika, the blue tick is represented only by several females and a male from two of these hosts).

Other wild animals: Hares (Tromsdorff 1914, Bedford 1932B, Cooley 1934). Zebra (Bedford 1932B). Bushpig (Santos Dias 1950B). Buffalo (Old 1909, Schwetz 1927B,C, Mettam 1932, Jack 1942).

BIOLOGY

Life Cycle

B. decoloratus is a one-host tick. Females lay their eggs on the ground. When larvae find a suitable host they remain on it, either on the dewlap and neck or on the ears, at the tip or along the upper edge of the pinna. On the ears, larvae are often associated with immature stages of R. appendiculatus. At this locus larvae molt to nymphs and nymphs molt to adults. Adults usually move to the belly and flanks of the host, and mate on the animal. The life cycle is completed entirely on the host except for oviposition, in from three weeks (A. Theiler 1911B) to a month (Lewis 1939B). Lounsbury (1905B) stated that females leave the host 23 days after having attached as larvae, but males may remain on the host for another month. He listed the pre oviposition period as six to nine days. Eggs hatch after five weeks and larvae molt one week after having completed feeding. Wintertime egglaying and hatching is much slower. Unfed larvae may survive for over eight months (Theiler 1949A).

Ecology

A. Theiler (1911) reported such a heavy infestation of B. decoloratus on a horse that it died of acute anaemia. Half of the ticks were collected; they weighed fourteen pounds. More recent literature on arsenic-resistance in South African blue ticks also frequently refers to and illustrates markedly heavy infestations of host animals.

Because of their unique life cycle, boophilids are readily controlled by dipping cattle, and there are numerous reports of the eradication of B. decoloratus from large areas. New control problems are posed, however, by the development of resistant strains.

From Theiler's (1949A) survey of conditions under which the blue tick exists in South Africa she concludes that the most im portant factor in limiting its spread is increasing aridity. In most parts of South Africa, the critical level is represented by an annual rainfall below fifteen inches. B. decoloratus is absent in deserts except for introductions that do not become established. It is present at all altitudes from sea level to high mountains, and can withstand both frost and high temperature. Similar though less detailed observations were reported by A. Theiler (1921). In tropical African forest, the blue tick occurs probably only in open, cleared areas (Theiler and Robinson 1954).

The data confirm Lewis' (1939) findings for Kenya, where B. decoloratus inhabits moist regions, highlands up to over 8000 Teet altitude, and forests and glades but seldom open, dry, scrub areas. In Kenya, it is also resistant to heat and cold provided moisture is available. In Ruanda Urundi the altitudinal range does not exceed 6500 feet (Schoenaers 1951B).

In the Belgian Congo, Bequaert (1931) found the blue tick to be so common that it was unnecessary to list all the localities from which specimens were secured. Yet Van Vaerenbergh (1954) reports this species as generally distributed in the Congo and Ruanda Urundi but represented by a small number of specimens or absent from many lots in his collections. The discrepancies in the inferences of these two authors undoubtedly result from differences in collection areas and methods, interests of collectors, number of ticks taken and hosts examined, and other factors. Sim ilar situations have provided widely differing reports for the in cidence of other species of ticks elsewhere, as for instance R. s. simus on cattle in Nyasaland and in South Africa and R. s. sanguineus on dogs in eastern and southern Africa. It is obvious ly impossible to generalize on population abundance in large areas and difficult to evaluate generalizations not supported by data. After having seen Dr. Bequaert's extensive collections, it should be confirmed that the blue tick is certainly numerous in many Congo areas and that it is uncommon or absent at high elevations and in dense forest areas.

In Nigeria this is said to be the second most common tick from domestic animals and represented 28% of the specimens collected from domestic animals in all Provinces (Mettam 1951). Only A. variegatum at 45%, is more common in these collections.

Wilson (1953) has stressed that the factors governing the dis tribution of this tick in East and Central Africa require further study.

In untreated Northern Rhodesian cattle, "blue ticks in all stages were present ..... throughout the full year's observation. These ticks quickly became very abundant, the cattle being gross ly infested through May, June and July. There was no evidence of decrease in infestation throughout the dry season apart from a slight decrease in late July and August. The blue tick infesta tion did not build up during the wet season". Matthysse (1954)

The red billed oxpecker or tickbird, Buphagus e. erythrorhyn chus (Stanley), which attends all of the larger herbivores except the elephant and hippopotamus, is a predator of some importance on B. decoloratus and on other economically important ticks. Of 58 tick birds examined in Tanganyika, 51 blue ticks were found in the stomach contents of thirteen; the number of ticks per stomach ranged from one to ten (Moreau 1933). In Kenya, van Someren (1951) found 38 blue ticks in stomach contents of four out of twelve of these birds that he examined. See p. 275 for a discussion of this sub ject.

REMARKS

Schulze (1936A) remarked that the spurlike prolongation of the male adanal shield is sometimes separated from the base in a position similar to that of the subanal shields of Hyalomma species. Two hundred and fifty males have been examined from various parts of Africa without seeing a similar condition. Schulze also (1932C) compared the adanal shields of B. decoloratus with morphological peculiarities of fossil Eophrynus. The triple capsule of the haller's organ in B. decoloratus has been described and illustrated by Schulze (1941). Double diagonal striations of the nerve fibers have been noted and illustrated by Kruger (1935). The blue tick has been employed by Gossel (1935) to delineate features of the eyes and their related cells in ticks. Abnormal specimens have been noted (Warburton and Nuttall 1909, and Bedford 1924A).

DISEASE RELATIONS

MAN: Evidence that this tick transmits boutonneuse fever

(Rickettsia conorii) appears to be entirely presumptive. The bite may in itself result in severe inflammation, but man is probably seldom attacked by this tick. Q fever (Coxiella burnetii) is claimed to have been found in specimens from Portugese Guinea.

CATTLE: Redwater or Texas fever (Babesia bigimina). Spirochetosis (Borrelia theileri). Gallsickness (Anaplasma marginale). Not a vector or heartwater (Rickettsia ruminantium). The virus of a specific transmissable petechial fever of cattle survives in this tick.

Spirochetosis (B. theileri). Not

HORSES, SHEEP, and GOATS: Spirochetosis a vector of equine piroplasmosis (Babesia equi

manni

PIGS: Possibly a vector of porcine babesiosis (Babesia traut

Domestic animals may be so severely irritated that their health is impaired and deaths from the bloodsucking of huge numbers of B. decoloratus have been recorded.

A toxin from the egg of B. decoloratus has been described.

IDENTIFICATION

Males are easily determined by the presence of a small taillike caudal appendage, which varies considerably in size, on the posterior body margin and by a narrow spurlike elongation of the internal margin of the adanal shield, which reaches to or more commonly extends beyond the posterior body margin. The unique, small bristle bearing protuberance on the internal ventral surface of the basal palpal segment is most important; this feature may be difficult to discern in small specimens and the bristles are often broken, though the knobs may usually be seen. Hypostome dentition is 3/3, rarely 3.5/3.5. Size is very small, about 2.7 mm. long and 1.5 mm. wide.