Gregson, J. D.

English

Journal of the Entomological Society of British Columbia

54 ENTOMOLOGICAL SOCIETY OF BRITISH COLUMBIA, PROC. (1951), VOL. 48, AUG. 15, 1952 when applied once as a drenching spray to three cows. However, when similarly applied at 0.75 and 1.5 per cent. of gamma isomer, benzene hexa-chloride did affect and kill the cows. Two Hereford heifers, thoroughly sprayed in eight treatments at four-day intervals with 1.5 per cent. chlor-dane emulsion, were not affected. In the same paper the authors re-ported that of ten cattle sprayed with a two per cent. suspension of chlor-dane at two-week intervals, three cows died after 10-12 days following the fourth spraying. Other cattle sprayed similarly with two per cent. of benzene hexachloride (12 per cent. gamma isomer) showed no apparent Injury. Radeleff and Bushland (1950) found tha t suckling calves were particularly susceptible to benzene hexachloride, toxaphene, and chlordane at various levels from 8.0 per cent. to 0.025 per cent. of the toxic ingredients. In this experiment the calves were sprayed until thoroughly wet. The meagre published results of work on this phase of the toxicity of the newer insecticides emphasizes a need for further investigation. To aggravate the situation, no standard-ized method of applying the insecti-cides has been attempted, for each group of workers has a different set of problems. For example, in the present experiment only one litre of insecticide was sprayed on each of the cattle, whereas Radeleff and Bush-land and Bushland et al wet their cattle thoroughly. Each group was guided by the limits of its purpose in performing one experiment. References Bushland, R. C, R. w. Wells, and R. D. Radeleff. 1948. Effect on Livestock of sprays and dips containing new chlorinated insecticides. J. Econ. Ent. 41: 642-645. Gregson J. D. 1946. Benzene hexachloride '(,"666") as an acaricide. Canadian Ent. 78: 201-202. Radeleff, R. D., and R. C Bushland. 1950. Acute toxicity of chlorinated insecticides applied to livestock. J. Econ. Ent. 43: 358-364. Shepard, H. H. 1939. The chemistry and toxicology of insecticides. Burgess Publish-ing Co., Minneapolis. 383 pp. FURTHER STUDIES ON TICK PARALYSIS' J. D. GREGSON2 Livestock Insect Laboratory, Kamloops, B.C Tick paralysis in British Columbia and adjacent territories, as in South Africa and Australia, has long remain-ed a disease of baffling origin. Though it is generally conceded that the symp-toms produced in the host are brought on by tm injection of a toxin by the tick, the reason why ticks of the same species vary in potency is still a puzzle. The solution to this mystery has been complicated by a series of factors which have included such neb-ulous conditions as are involved in different host and tick species, host susceptibility, and host immunity. 1 Contribution No. 2918, Division of Entomology Science Service, Department of Agriculture, Ottawa; Canada. 2 Officer·in·Charge. Zumpt (1950) even questions whether these factors are the only ones, and as he suggests, the physiological con-dition of the individual tick seems to be of considerable significance, a hctor which has resulted in studies too frequently containing so many unknowns that no logical pattern is apparent. This, together with the shortness of the annual period of na-tural tick activity, has rendered pro-gress in the etiology of the disease slow. Nevertheless, each year some advance has been made and consider-able data gained toward the under-standing of this interesting phenom-enon. In British Columbia tick paralysis is caused by the female of the Rocky ENTOMOLOGICAL SOCIETY OF BRITISH COLUMBIA, PROC. (1951), VOL. 48, AUG. 15, 1952 55 Mountain wood tick, Dermacentor an-dersoni Stiles, and is mainly a disease of cattle. If these animals are pas-tured on tick-inhabited ranges during the active adult tick season of March and April, they become infested with large numbers of the parasites. These congregate in dense masses on the heads and shoulders of the victims and attach for their seven-to-ten-day blood meal. It is toward the end of this period, when they have become replete with blood, that they may paralyse their host. Sheep, dogs, and humans are also affected, but usually on these hosts there are few ticks o-r only one. This species of tick mates while feeding, which, as shown by Gregson (1944), enables the female to engorge to repletion much more rapidly than when deprived of a male. The feed-ing period of a mated female is approximately seven days, after which it drops from its hosts, whereas an unmated tick remains attached, half-engorged, for several weeks. For ~ ;ome time it was thought that fast-feeding, mated females were more virulent than the slow-feeding, unmated ones. This view is, however, weakened by the facts that in human paralysis the male tick is rarely present and that in most instances the causative tick is only haH-replete at the onset of paralysis. TEST ON SUIT ABILITY OF HOSTS During the past few springs further attempts have been made at the Kam-loops laboratory to demonstrate the conditions responsible for the produc-tion of paralysis. Since so many fac -tors appear to be involved in the occur-rence of paralysis in tick-infested animals, one of the first steps was to find a host that is subject always to paralysis. To permit large-scale in-festations involving animals on which ticks had not previously fed, small labora tory animals ,vere sought. r t was with some degree of surprise that white mice were discovered to be ideal hosts oi the adult ticks, for never in nature has this stage of ti ck been taken from the numerous wild mice present in tick-infested areas known at the Kamloops laboratory. Though the ticks in the laboratory had to be protected from the actions of their hosts by large rubber discs placed around the animals' necks, the cleanly nature of mice does not prevent other species of ticks in nature from attach-ing and engorging. The successful application of this discovery was short-lived, for it was found that though rapidly engorging, mated ticks did kill the mice, death was apparently clue to a severe anaemia, as shown bv blood counts, and slow-feeding ticks pro-duced no typical symptoms of paraly-sis. These results covered 37 infesta-tions Of 18 mice infested with mat-ing ticks, ten died ancl eight grew only sluggish by the time the ticks became replete. Nineteen, infested with single female ticks, were un-harmed, and at the end of the seven days (the normal period for paralysis to appear) bore half-engorged speci-mens. One mouse harboured five and another two females for the same period without apparent ill effects , though a third with four females died - presumably because of the large blood meals of the ticks. Mice, then, apparently do not fill the need for a host susceptible to paralysis ·-unless , of course, the ticks used in this experiment were for some reason not capable of producing paralysis. Rabbits and guinea pigs appear to be immune to tick paralysis, as is sug-gested by the lack of symptoms of this disease during the course of infesting these hosts with thousands of ticks in spotted fever studies at the Rocky Mountain Laboratory, Hamilton, Mon-tana (W. L. Jellison, personal com-munication), and during smaller-scale infestations at Kamloops. Dogs are relatively susceptible to tick paralysis ancl would undoubtably form conven-ient test animals were it not for the difficulties of procuring and maintain-ing them in sufficient numbers. Tn-festations on each of six puppies causecl a paralysis in three of the hosts, on which one, four, and two ticks had attached. :;6 ENTOMOLOGICAL SOCIETY OF BRITISH COLUMBIA, !>ROC. (1951), VOL. 48, AUG. 15, 1952 TESTS ON LAMBS In 1951, 30 lambs were available for further adult tick feeding observations at Kamloops. Though previous ex-periments had shown that all tick-infested lambs do not necessarily be-come paralysed, at least s.)me are paralysed under favourable condi-tions. METHODS AND DATA OF INFESTATIONS The ticks in these experiments on lambs were confined on the hosts by dome-shaped screen capsules, which were anchored to the surrounding wool by linen threads. To provide optimum conditions for the ticks, each capsule was placed over a clipped area tha t had been washed free from na tural grease. A dampened pad of absorbent cotton served to maintain the humid-itv until the ticks had attached. Un-le~s these precautions were taken a large number of the ticks died be-fore attaching. Such mortalities were excluded from the studies, the results of which are tabulated below. Summary of infestations of indi-vidual lambs, various feeding rates, and paralysing powers of engorging females (Complete data of this experi-ment are available from the author) : 1. Infested April 4, 13, 27 with 5, 4, 2 ~ and 5, 0, 20- respectively. Three* females fed rapidly. No paralysis. 2. Iniested April 26 with one paIr. Female fed rapidly without pro-ducing paralysis. 3. Tn fested March 28, 31 , April 7 with 5, I, ° ~ and 0, 0, 200- resp. N one fed rapidly. No paralysis. 4. Infested April 16, 26, May 8 with 6. 1, 8 'jl and 0, 1, 80 resp. Seven females fed rapidly. No paralysis. 5. Infested April 13, 13, May 3 with 4, 0, 6'jl and 0, 4, 10 0 resp. Two females fed rapidly. No paralysis. 6. T nfested April 13, 13, 13, 25 with 6, 0, 1, 1'jl and 0, 12, 1, 10 resp. Two females fed rapidly. )J() paralvsis. 7. Infested April 11, Mav 3 with 1, 1, 'jl and 2, 30 resp. noth females fed rapidly. )Jo paralysis. * Failllre of all female s paired with male:; to feed raridly is probably due to a delay in mating. 8. Infested April 14 with 10 ~ and °.0 . None fed rapidly. No paraly-SIS. 9. Infested April 16, 28, May 8 with 3, 2, 8 'jl and 0, 1. 8 0 resp. The two females of the second group paralysed the lamb moderately when only half-replete. Recov-ery followed their removal. Five females of the last group fed rap i dIy, causing no further paralysis. 10. Infested April 14, 30 with 6, 1 ~ and 3, 1 'jl resp. Of the first group, one female fed rapidly, causing a slight paralysis which disappear-ed upon its release. Two subse-quent females fed rapidly, caus-ing no paralysis. 11. Infested April 14 with 3 'jl and ° 0 . None fed rapidly. No paralysis. 13. Infested March 28, 31, April 13, 30, lVIay 10 with 5, 1, 5, 2, 10 'jl and 5, 1, 0, 1. 0 0 resp. One female of the first group fed rapidly causing a sligh.t paralysis. Four slow, and a subsequent fast feed-er produced no symptoms. The lamb finally was paralysed severe-Iv bv five slow-feeding ticks of the -third group. Paralysis re-mained as the ticks were taken off at hourlv intervals until the last was off. Two fast-feeding females of the fourth group and ten slow feeders of the last pro-duced no further paralysis. 14. Infested April 11, 27 with 1, 1 'jl and 2, 10 resp. Roth females fed rapidly, the first producing a slight paralysis, the second none. 17. Infested May 3 with 3'jl and 20-. Two females fed rapidly. No paralysis. 18. Infested April 12, 28, May 8 with 1, 1, 7 'jl and 2, 2, 80 resp. First two females fed rapidlv, causing no paralysis. Seven females of the last group fed rapidly, pro-ducing severe paralvsis. 19. Infested April 30, May 8 with 2, 8 'jl and 2, 80 resp. All females fed rapidly, each group producing a slight paralvsis. 20. Infested April 25 with 2 pairs. noth females fed rapidly. No paralysis. ENTOMOLOGICAL SOCIETY OF BRITISH COLUMBIA, PROC. (1951), VOL. 48, AUG. 15, 1952 57 21. Infested April 13 with 1 pair. Female fed rapidly. No paralysis. SUSCEPTIBILITY OF THE LAMBS The lambs used in these experiments were as uniform a group as practical inasmuch as they were much of aft age and none had been exposed to ticks before. Some o f the lambs that were unaffected by ticks during the tlrst infestations were susceptible to paralysis late r (Iambs 9 and 18) . It is, howev er, unlikely tha t this later re-sponse was due to sensi tizatioJ:, since six others (lambs 1, 3, 4, 5, 6, and 7) did not become paralysed afte r re-peated infestations during similar periods. Indifference to tick paralysis because of development of host im-munity can probably be ignored also , since paralysi s was produced twice within eight days in two lam bs (1~ and 19). These facts sugg':! st that some factor in the tick, rather than in the lambs, was responsible for the paralysis in the above instances. Th ough this assumption is later moderat ed by indica tions of a host resistance, it does o ffer a theo rv that is valuable fo r further progress, in view of the scantiness of substantial evid ence. VIRULENCE OF THE TICK I f, then , the presence of paralysis is considered to be due to a condition within the tick, attention can be di· rected toward a compa rison of the virulence of the sexes. Though males are frequently associated with fem ale s in paralysis cases, at the Kamloops laboratory there is no record of paralysis caused by males themselves. 1 n the experiments under discussion 32 male ticks were fed on lambs 'without apparent symptoms of paralysis. Pre-sum ably the sparsely fe edin g male tick can be omitted as a direct causa tive agent in this disease. In-directly, it was felt it might consti-tu te a -factor by increasin g the feeding rat e of the female . Assum ing, now , tha t paralysis is cau sed only by the female tick, an analysis can be made of the effects of mated and unmated ticks on the host to determine whe ther or no t the feeding rate is related to the virulence of the tick. In 28 separate infesta-tions involving 80 pairs o f ticks (fed in single pairs or in series up to ·ten pairs on 16 lamhs) SO ticks mated and engorged rapidly enough to drop re-plete in seven days. Of these S0, only 11 were possibly in volved in the pro-duction of the six cases of paralysis that resulted. It is possible that actual-ly only one tick was involved in each case, so that the ratio of virulent mat-ed ticks to benign ones might then be approximately one to eight. In ten other infes tations involving 52 females without males (fed in num-bers from one to ten on eight lambs), paralysis occurred in one lamb (13) o n which five ticks were feeding. The possibility that all these ticks ' w ere involved in the production o f the paralysis cannot be dismissed, since the symptoms did not subside until the las t tic l ~ was removed. If. how-ever, only this last tick was impli-cated, the ratio of virulent unmated ticks to benign ones was one to fifty-two. The above data suggests that ma ted, rapidly feeding fe male ticks are more likely to cause paralysis in lambs than slower-feeding' ones. As judged from this laboratory's reco rds, the fact that slow-feeding, solita ry females are so virulent in human infestations, where a tick sel-dom engorges without causing par-alysis, suggests that man is more susceptible to the action of 1 he tick than lambs-a theory that agrees with the mentioned variation in sus-ceptibility among different species of animals. Lambs, then, are moderate-ly resistant, since, ou t of the eight cases of paralysis m entioned , only two were severe enough to produce a loss in the use of the limbs; the remaining lambs exhibited only an unsteady gait. I n cont rad iction to the aforementioned apparent uniformity of hosts, this latter symptom suggests that certain lambs had a g reater resistance to the toxin. This r esistance may even have masked the potentialities of seemingly innocuou s ticks. According to records at the Kamloops laboratory, pa ralysis in cattle is invariably caused only by 58 ENTOMOLOGICAL SOCIETY OF BRITISH COLUMBIA, PROC. (1951), VOL. 48, AUG. 15, 1952 clusters of ten to 50 ticks and it is doubtful whether these animals could be paralysed by solitary specimens. However, not all animals with heavy infestations will become paralysed -suggesting again an individual re-sistance. The data for lambs 10, 13, 14, 18, and 19 substantiate a variation in virulence among ticks. At the same time, there is an indication that a paralysed animal is so weakened that it may then be affected by ticks, which on a healthy animal, would not be considered virulent. This is evident in animals on the range which often remain prostrate for several hours until the las t ticks are removed, and then make a rapid recovery. This could be the case in lamb 13. Lamb 9 presented an interesting op-portunity for a further experiment in that paralysis commenced when the two engorging ticks were only half-replete. The ticks were transferred to lamb 1, which, though having been subjected to ticks, had not yet been paralysed. The virulent ticks attach-ed, and dropped within a day-but did not cause paralysis. Similar re-sults occurred in a previous year when a partially fed tick from a paralysed child was induced to attach to a mouse, whereupon it mated and fed rapidly without harm to its second host. Again there are too many unknowns to establish a reason for this behav-iour. It appears that a virulent tick can paralyse only the host upon which it commences to engorge. In summary, it is assumed that tick paralysis is brought about in the host by a toxin secreted by the engorging tick. It appears that the production of tick paralysis in an animal depends on a combination of host sus ceptibility and tick virulence; and that where the host is relatively resistant, as in sheep and cat tie, only a certain por-tion ot rapidly feeding ticks produce the symptoms, whereas in humans, considered to be more susceptible, solitary, slow-fe ~ding ticks are suffi-cient to cause paralysis. The conflict-ing evidence concerning the va rying resistance of the host and the unknown virulence of the ticks makes it difficult to arrive at any conclusion. Referencea Gregson, ]. D. 1944. The influence of Zumpt, F., and D. Gl ajchen. 1950. South fertility on the feedin g rate of the female African Merl. J. 25 :1092-1094. o f the wood tick, Dermacentor andersoni Stiles. 74th Ann. Rept. Ent. Soc. Ont., 1943, pp. 46-47. A REVIEW OF STUDIES ON THE SYSTEMIC CONTROL OF LIVESTOCK INSECT PARASITESl G. B. RrCH2 Livestock Insect Laboratory, Kamloops, B.C. If, without causing harm to the animals, it were possible for a stock-man to introduce into the diet of his livestock some substance that was toxic to bloodsucking arthropods feeding' upon these animals, he would find a solution to one of the important problems of animal husbandry. Eco-nomic entomologists have recently devoted a great deal of effort toward the attainment of this ideal, and the 1 Contribution No. 2912. Division of Entomology, Science Service, ])epartm.ent of Agriculture, Ottawa, Canada; presented at the ':Oth Anniversarv h-ieetings of the Entomologic:1l Society of Briti sh Columbia ill Vancouver, June' 14·16, 1951. 2 Assistant En tomologis t. investigations seem to indicate that it may be possible to achieve it. However, the problem is no t simple. Many difficult biochemical and toxi-cological factors must be studied and their roles elucidated before the prob-lem can be solved. Because of these factors, the entire matter must be ap-proached with caution. A full dis-cussion of these aspects is beyond the scope of this paper because it is my intention only to review som e of the more important studies that have been made in the past. The first important contribution is that of Knipling (1938), who reported 

Further studies on tick paralysis

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Further studies on tick paralysis

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Journal of the Entomological Society of British Columbia