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It is significant that the Russian worker considers the rabbit to be an atypical host of immatue stages of H. excavatum. This is far from true in North Africa and Arabia, where hares and other smaller animals are frequently parasitized (rabbits do not occur here). Most probably smaller animals are also parasitized in Russia but workers there, who have been occupied chiefly with veterinary problems, have failed to investigate this possibility. Indeed, it seems that a diametrically opposed, theoretical con. clusion might be drawn;

Under primitive conditions, in areas lacking large
numbers of domestic animals, H. éxcavatum spends part
or all of its life cycle on small animals, usually no
larger than hares. In these situations it udergoes a
one or two_host type of life cycle. However, when herds
of larger domestic animals are present in the range of
this tick, the adults and sometimes the immature stages
may be confined to these animals. On these larger ani_
mals, H. excavatu undergoes a three.host type of life
cycle, which is an atypical one for the species, in.
fluenced as it is by the availability of hosts due to
human activities.

This matter is obviously in need of further investigation.

With regard to the seasonal cycle of H. excavatum, the

aforementioned authors working in Iran, Egypt, and Falestine,

as well as Serdyukova (l946B) working in the semi_deserts of Tadzhikstan, agree that engorged nymphs and young adults hibernate in cracks and crevices of buildings during the winter; the Soviet observer states that larvae may also overwinter under these conditions. In Russia, hibernating ticks were taken in,/ among, under, and in association with wooden fixtues of animal enclosures, but not under cakes of dung plastered on loose walls. When these structures were removed the incidence of ticks found in these yards the following summer was only a fraction of what it had been the previous year. In the deserts of Egypt engorged nymphs and ufed adults overwinter in rodent burrows.

In sping, ticks that have hibernated venture forth to feed. Under experimental conditions, if they are removed to a warmer

place during the winter nymphs molt and adults feed. In Egypt, wild nymphs do not normally molt until almost summertime, pos. sibly because of cold nights during early spring. By late March, however, females begin to feed, and at this time they may oviposit very shortly after dropping from the host - as soon as seven days afterwards. The incubation period may be as short as 27 days, so that in May new larvae and last year's nymphs can be found feeding. Under the Russian conditions already mentioned, oviposition does not commence until July or August and it appears that there is only a single generation a year in those climes. In Tadzhikistan

(Lototsky and Pokrovsky 1946), adults of H. excavatu (= H. anatolicu) infest cattle from the end of_Fe5ruary to November, and larvae and nymphs from July through September; all stages are most numerous early in August.

Larvae feed for from fou to six days (32°C., 75% R.H.) according to Feldman.Muhsam, but the Russian observer reported only two to four days in nature. Larvae melted six days after leaving the host (30°C.), after four or five days at 38°C., and after thirty to fifty days at l7.5°C. (after six to twelve days in Russian observations). Nymphs fed a week later and remained on the host from nine to twelve days (four to six days in Russia) but the time between dropping and melting to the adult stage varied-greatly (twelve to twenty days in Russia).

At 35°C., the molt to females occurred in from eleven to 24 days and to males in from twelve to 35 days. At 30°C. both sexes appeared between eleven and 56 days after nymphs dropped from their host. The duation of one generation at 32°C. was estimated at 116 days, but it was concluded that umder field conditions some of these stages may be shorter and there may be three generations a year.

Parthenogenesis in H. excavatum has been observed by Pervo. maisky (1949) who foumd'that a few F1 females could be reared from eggs laid by females in the absence of males.

Ebology

Feldnuuxliuhsam (1947) observed that unfed larvae and nymphs are much more sensitive to humidity than to temperatue. At any

temperature survival of unfed imature stages increases with higher humidity. In laboratory tests, larval longevity varied between two and 241 days (mean 1.25 and 162.6 days), nymphal longevity between ten and 246 days (mean 6.8 and 149.2 days). The author considered that under undisturbed natural conditions survival would have been longer than in these tests in which daily counts were made.

Nymphs are less susceptible than larvae to low humidity.

The length of nymphal life increases directly with humidity and inversely with temperature. Other life history and hibernation studies by Feldman;Muhsam (1949) are of interest, but since they apply to frigid Palestinian winter conditions that do not occur in the area under consideration this work is not presently per. tinent.

Serdyukova (l946A) observed ticks detaching from their hosts at night; larvae and nymphs mostly between nine and eleven o'clock in the evening. A nuber of larvae and nymphs placed on a calf in the morning became fully engorged during the day but*remained on the calf when darkness set in. This behavior, probably an adaptation to local climatic conditions, protects the ticks from exposure to the direct rays of the sun, which are fatal to them. They are apparently inactive duing the hot part of the day, and attach to hosts at night as has been recorded for other H alomma species under desert conditions. In an isolated plot only slightly over five percent of a counted nuber of unfed ticks attached to calves between noon and sunset.

H. excavatu is obviously a tick of xeric regions not necessarily associated with domestic animals although populations are considerably larger where these animals occur. Experience in the comparatively 1ightly_vegetated desert areas of the Mediterranean littoral of Egypt, where it infests rodents in their burrows, indicate this tick's habits away from large, dense flocks of domestic animals.

In Transcaucasia, H. excavatu Q: H. anatolicu) is typical

\ of various desert, semidesert, and steppe formations, but does

not occur in forested zones (Pomerantzev, Matikashvily, and Lototsky 1940). This agrees with observations in Anatolia (Hoogstraal, ms.). with respect to altitudinal distribution in Trans

caucasia, these authors say H. excavatu falls in group in which the ‘upper limit of distribution ..... is ..... inversely pro. portionate to the moisture of the climate and to the amount of rainfall and directly poportionate to the height of the snow line during the summer period".

In Armenia, H. excavatu.(= H. savi i armenoriu) is found

in pasture at 65OO feet eIevation_ g er (Lototsky and Popov 1934). During the present study it has been found at similar heights in Sinai, Yemen, Anatolia, and Eritrea.

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Adults feed on cattle chiefly on the scrotu and perineum and in the inguinal and axillary areas. Nymphs generally feed on the neck, chiefly along its crest. Larvae are not commonly found on Egyptian cattle.

Note: The following section is ancillary to further remarks on the ‘subgenus Hyalommina" (page

In Egypt (Hoogstraal, ms.), larvae and nymphs of H. excavatum are frequently found completely overgrown by rodent host skIn.

This phenomenon is especially common among young jirds, Meriones shawi shawi Duvernoy, and sometimes on young fat sandrats, Psammo.

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s o. o sue, on the Mediterranean littoral. During springtime

most every nestling jird in the vicinity of Mersa Matruh is infested in this manner. The ticks can be detected by lups uder the skin, most frequently around the neck, axillary areas, shoul. ders, and flanks. Some of these rodents have as many as 22 in» matue ticks under the skin. The host skin may partially or completely enclose the ticks*, which are almost always misshapen when removed. Some nymphs extricated from uder the skin of jirds have molted to adults in our laboratories. They have in. variably been tiny, weak, misshapen, poorly developed, pale spec. imens, which, if identified according to criteria offered by Schulze (1919), would be H. rhipicephaloides Neumann, 1901, in the subgenus Hyalommina. _

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*Nuttall (l9l4B) has quite accurately described this pocesses as an oedematous swelling of the host skin, as a result of irritation

when the long mouthparts of Ixodes (and H alomma) ticks reach firm subcutaneous connective tissue; the oedematdus swelling may gradual.

ly engulf the feeding tick.

Schulze (1921) recognized this growth phenomenon for mate. rial of “H. rhi ice haloides" from a "steinbockF (probably meaning an ibex) Hew~ ea in Palestine, although he continued to apply a species nae to these runts. Yet, Schulze and Kratz have presued to refer to this as a "half.endoparasitic type of para. sitism" by ticks. Large nuber of ticks were found in pale red. dish cysts in the ibex's subcutaneous tissue, especially in the aillae. Holes in the host skin could not be detected.

In several instances we have found cast larval skins en. casing subdermal nymphs. Young jirds raised to adulthood in the laboratory yielded dead H. excavatu in the middle of the summer when the hosts were sacrificad, and nymphal skins were found around them. we have no evidence that a H aloma tick overgrown by the host's skin can force its way out.tEFough the skin.

Pavlovsky, Pervomaisky, and Chagin (1954), in preliminary studies, have also indicated that when H. excavatum C: H. anato. licu) feeds in large numbers on a restrictgd area of the Host, poorly developed specimens result. Females especially do not fully engorge and may even die due to inflammation of the host skin. When other species also compete for a restricted area of the host skin, an additional antagonistic factor increases the chances of abnormal development or death.

Prolonged infestation on rabbits by_H. excavatu under lab. oratory conditions does not confer host immuity, preventing en. gorgement by subsequent larvae, against this species or against Dermacentor pictus (Chabaud 1950A, Brumpt and Chabaud 1947).

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REMARKS

A capillary tube arrangement, which has proved sucessful for the artificial feeding of adults of H. excavatu for physio. logical and disease.transmission studies, has been described by

Chabaud (19501) .

Schulze (19320) illustrated the leg segments (of ‘H. anato. lieu?) to support theories of tick ornamentation. In'the same

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