Larval biology of rhipicephalus (Boophilus) decoloratus (Acarina: Ixodidae) in Free State Province, South Africa

The objective of this study was to determine certain aspects of the biology of Rhipicephalus (Boophilus) decoloratus larvae under laboratory and field conditions. Larvae allowed 48 h to select a vertical questing substrate preferred 90 cm rods in length to those of 60 or 30 cm, while in a separate experiment migration from rods 5 cm or 25 cm in length to rods 45 cm in length continued between 48 h and 72 h after larval release. Hatching of the larval progeny of engorged female ticks exposed to ambient field temperatures during the period June to August, occurred synchronously during the third or fourth week of November. With a single exception, larvae that hatched during November and between April and July survived for 38 days or longer, while those that hatched from December to March survived for 31 days or less. Questing larvae were present on vegetation throughout the year, with most being recovered during January and February. Parasitic larvae were present on cattle from October to May with most being collected during January and February.     

Seasonal dynamics of the free-living phase of Anocentor nitens at Pedro Leopoldo, Minas Gerais, Brazil

An understanding of seasonal dynamics in the free-living phase of the tropical horse tick, Anocentor nitens, is vital for effective control measures. This study examines seasonal changes in the oviposition and incubation periods, eclosion rates, reproductive success, and larval survival in the free-living phase during the period June 1995-July 1997. Ten engorged female ticks, placed individually in wire-gauze tubes, were exposed in a field of Brachiaria decumbens fortnightly each month, and monitored to measure the duration of the various reproductive parameters, and success. Larval abundance was estimated indirectly, through the percentage of females with viable progeny, and directly by using a flagging method. Duration of the free-living cycle ranged from 12.3 weeks (October and December) to 23.5 weeks (March). The cycle was prolonged in cold and dry months. Larval survival was longer from February to July, and reduced from August to February. Oviposition was recorded in all months, and the egg production index ranged from 26.7 to 47.1%. The eclosion rate ranged from 0.1 to 76.6% in different months. Monthly estimates of larval abundance in the pasture were similar for the two methods used, being higher in months with higher temperatures, relative humidity and rainfall.     

The sex ratio of Amblyomma cajennense (Acari: Ixodidae) with notes on the male feeding period in the laboratory

To evaluate the sex ratio of field collected nymphal Amblyomma cajennense ticks, we collected 5326 engorged nymphs from naturally infested horses in Pirassununga county and allowed them to molt to adults in the laboratory. They yielded a sex ratio of 1:1.83 (M:F). Three and two engorged females were collected from horses pastured at Pirassununga county and from tapirs pastured in Sorocaba county, respectively. These females were allowed to oviposit and their progeny were reared until the adult stage in the laboratory. Engorged females collected from Pirassununga yielded a sex ratio of 1:1.57 (M:F) and a sex ratio of 1.14:1 (M:F) were obtained for those ticks collected from tapirs. In addition, unfed tick larvae were collected from Pedreira county and reared in the laboratory until the adult stage. This collection yielded a sex ratio of 1.11:1 (M:F). These results showed significantly different (P<0.05) sex ratio constitutions among different tick populations. Laboratory rabbits were infested once with A. cajennense male ticks, which showed feeding periods varying from 7 to 86 days. During this period, the rabbits were re-infested regularly with A. cajennense female ticks. A total of 179 engorged females were collected from the rabbits and their engorged weight, feeding, preovioposition and egg incubation periods, weight of deposited eggs, percent of hatched eggs and egg production efficiency were compared to the male feeding period and to the number of live males present on the host. None of the female variables were affected by the male feeding period. Male ticks remained fertile for the whole feeding period. Percent of hatched eggs was the only female variable that significantly decreased as the number of live males decreased on the host. The results showed that although some A. cajennense populations are composed of more females than males after molting, this female predominance is compensated by a long male feeding period and maintenance of its reproductive performance.     

Comparison of the reproductive biology between acaricide-resistant and acaricide-susceptible Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

The reproductive fitness of Rhipicephalus (Boophilus) microplus (Canestrini) strains resistant to organophosphate (OP), pyrethroid (P), or formamidine (F) acaricides was compared to an acaricide-susceptible (SUS) strain to determine whether the acquisition of resistance affected reproductive fitness in the resistant strains. The SUS strain females had a 3.0 days preoviposition period, a 12.1 days oviposition period, a 22.5 days egg incubation period, a mean of 3670 eggs per female, and a mean percentage egg hatch of 78.1%, which were all remarkably similar to these same parameters reported for this species throughout the world. The reproductive biology of the P-resistant strain (PYR) and the F-resistant strain (FOR) were, for the most part, similar to those of the SUS strain. In the few instances where statistical differences did occur there was little evidence that the variation had any biological basis that could be attributed to a reduction in fitness related to resistance to P or F acaricides. Although the comparison of reproductive parameters of the OP-resistant strain (OPR) and the SUS strain identified statistical differences between the mean egg incubation and oviposition periods, the magnitude of the differences was not sufficient to conclude that the OPR strain was biologically less fit than the SUS strain. However, the OPR strain produced 30% fewer eggs (2562 eggs per female) than the SUS strain (3670 eggs per female) indicating the acquisition of resistance placed the OPR at a selective disadvantage relative to the SUS strain. This coupled with a lower, though non-significant, egg hatch was used to predict there would be a reduction of at least 34.1% in larval numbers available to potentially re-infest subsequent cattle than were available from the SUS strain. These data may aid the development of management strategies that can be used to control OP-resistant ticks.     

Maturation of Theileria sergenti in salivary glands of Haemaphysalis longicornis induced by temperature stimulation

The parthenogenetic Haemaphysalis longicornis larvae engorged on cattle naturally infected with Theileria sergenti were reared at 24 degrees C. The resultant nymphal ticks were incubated at 37 degrees C to clear the effect of incubation on the development and maturation of sporozoites. The sporozoites in the salivary glands of the nymphal ticks exposed to 37 degrees C for 16 days were observed by the methyl green pyronin staining method. The ticks exposed to 37 degrees C were ground up in a mortar and the supernatant of the tick suspension in PBS was inoculated into cattle. The cattle showed parasitemia and specific antibody response 18 days after inoculation. Consequently, the parasites in the tick salivary glands became infective to cattle by incubating infected. H. longicornis nymphs at 37 degrees C.     

Studies on ticks of veterinary importance in Nigeria. VI. Comparisons of oviposition and the hatching of eggs of Hyalomma species

Fully engorged Hyalomma spp. in Nigeria oviposited greater numbers of eggs than those partially engorged. Hyalomma impressum was a more prolific egg layer than H. rufipes, H. impeltatum and H. truncatum. The variations in the egg output as well as the recognizable peaks in the number of eggs during oviposition were described for each species. No species of Hyalomma below the engorged weight of 0.2 g oviposited; oviposition started with ticks of weight 0.3 g. Eggs produced by ticks weighing below 0.3 g did not hatch; the highest percent egg eclosion occurred with ticks of weight 0.6 g (H. rufipes) and 0.7 g (other Hyalomma species). The pre-oviposition, oviposition and eclosion periods were shortened when eggs were laid and incubated at high temperatures, although the number of oviposited eggs did not increase significantly. At the standard temperature of 24 degrees C, the longest eclosion period was seen in the eggs of H. rufipes (41 days) while those of H. truncatum, H. impressum and H. impeltatum were similar to each other (29 days). Only eggs of H. rufipes hatched at an incubation temperature of 15 degrees C. Eggs of Hyalomma species laid at the same time hatched over a 2--4 day period, except at 15 degrees C when the hatching period of H. rufipes lasted 10 days. The eclosion period was longest in the earlier ovipositions and shorter in the later ones. It is suggested that some intrauterine larval development might have started in the eggs before they were released at a later oviposition period. The percentage mortality of eggs at various temperatures showed that eggs of H. rufipes were more tolerant of low temperatures than those of H. impressum, H. truncatum and H. impeltatum, while the eggs of the latter 3 species were more tolerant of high temperatures than those of H. rufipes. The relevance of these results of the distribution and abundance of the Hyalomma species in Nigeria was discussed.     

Life cycle of the tick Amblyomma parvum Aragão, 1908 (Acari: Ixodidae) and suitability of domestic hosts under laboratory conditions

Amblyomma parvum is a widespread Neotropical tick found on several domestic animals and is known to harbor a Rickettsia species of yet unknown pathogenicity. However its life cycle on, and suitability of, several of these hosts has not been described. In this work the biology of A. parvum is presented when fed on seven domestic hosts (chicken, dog, rabbit, horse, guinea pig, cattle and goat). The complete life cycle of the tick varied from 96.8 to 102 days. Highest engorgement weight of larvae was from ticks fed on horses and that of nymphs from guinea pigs. Highest larval yield was from guinea pigs and that of nymphs from horses. Engorged female and egg mass weights, yield and conversion of female weight to eggs rates were the highest in dog ticks and the lowest in goat ticks. The highest egg hatching rate was seen in ticks from dogs and the lowest in ticks from cattle. Overall it was seen that dogs were the best host for adult A. parvum ticks, and guinea pigs for immatures. Horses were also shown to be a good host for all tick stages. It can thus be affirmed that A. parvum is a host generalist tick, and its distribution is probably determined by environmental requirements rather than by hosts.     

Development of Hyalomma lusitanicum under laboratory conditions

At the constant temperature of 25 degrees C and relative humidity (RH) of 84%, the average pre-oviposition period of Hyalomma lusitanicum was 47 days, the oviposition lasted an average of 26 days and the total egg production was an average of 6320 per female. At 16 degrees C the females did not lay eggs at all, but those which survived for 1 year and were transferred thereafter to 25 degrees C and 84% RH laid viable eggs. At 35 degrees C, the oviposition was identical at all levels of RH tested (25, 62 and 93%). At 25 degrees C, the pre-oviposition period was shorter at 93% RH, and the number of eggs laid was fewer at 25% RH. The eggs hatched in 32-40 days, the hatching percentage being lower in batches of eggs laid at the beginning and at the end of the oviposition period. The larval and nymphal moultings were not influenced by the type of host. As the temperature increased, the pre-moult period became shorter. The engorged larvae were more sensitive to the low RH than the engorged nymphs, whose moulting percentage was always greater than 72 in all regimes. Low temperature and high humidity had a favourable effect on the survival of unfed nymphs. The female-to-male ratio was 1:2. Hyalomma lusitanicum always behaved as a 3-host tick. The adults did not engorge on rabbits. The female ticks engorged on calves weighed an average 543 mg. Ticks maintained at 25 degrees C and 84% RH and engorged on calves completed the life cycle in 138-196 days, which does not include the period of chitinization of about 30 days. More than half of this period was spent in egg laying and hatching.     

Studies on the critical water mass, rehydration capability and potential, acute chill tolerance and supercooling point of Argas (Persicargas) walkerae (Acari: Argasidae)

The critical water mass, defined as the water mass remaining in a dehydrated tick in the non-ambulatory state, differed only slightly between light and heavy mass groups of Argas walkerae and averaged 23.6% and 23.2%, respectively, in males and 28.4% and 28.0%, respectively, in females. All ticks survived dehydration to 50%, 75% or 100% of their critical water mass, and 95% of them rehydrated during their subsequent incubation at 95% relative humidity (RH) and 28 degrees C for 14 days and regained their ambulatory status. Unfed adults were able to balance water loss frequently over a period of several months. When ticks were repeatedly dehydrated at 0% RH for 14 days, females and males suffered 50% mortality after 16 and 19 cycles of de- and rehydration, respectively, over a period of 278 days and 337 days, respectively. Water itself was not attractive to either dehydrated or non-dehydrated ticks and drinking was not observed. After submergence in water for 3 days, most of the dehydrated adult ticks gained mass. Judged by 50% mortality, larvae tolerated short-term extreme chilling to -24 degrees C, nymphs 1 to -22 degrees C, nymphs II to -20 degrees C, females and males to -19 degrees C. None survived tissue freezing. At a chilling rate of 0.3 degrees C/min, mean supercooling points (SCP) ranged from -25.9 degrees C in eggs to -16.5 degrees C in unfed females. The SCP of all other stages was significantly higher than that of eggs. Mean SCPs of unfed adult ticks dehydrated to 50% or 75% of their critical water mass were significantly lower than that of fully hydrated ticks. The SCPs of ticks acclimated by several weeks exposure to 0 degrees C or to 38 degrees C were significantly lower than those of adult ticks kept constantly at 28 degrees C.     

Parasites of domestic and wild animals in South Africa. I. Oestrus ovis in sheep

Separate groups of 3 oestrid-free lambs were exposed to infestation on irrigated pasture for periods of approximalely 33 days each over30 months, and on dry-land pasture for approxomately 42 days over a period of 18 months. With some exceptions, the lambs slaughtered from October-June were found to be infested with Oestrus ovis while, with one exception, those slaughtered from July-September were free. A minimum of 4 sheeps' heads, obtained weekly over 24 months from the Pretoria Municipal Abattoir, was examined for infestation. Of a total of 542 heads examined, 73,4% were infested, having a mean burden of 15,2 larvae. Mean larval burdens were slightly greater in hornless than in horned sheep in Dorper-type than in Merino-type sheep, and in lambs than in sheep with 2 or more permanent incisors. The largest larval burdens were recovered from sheep slaughtered during May and June and the smallest during September and October. The greatest number of 1st instar larvae were recovered during May and June and the smallest during September, but those recovered during the latter month were the largest. With one exception, mature larvae which pupated after 21 March or before 16 August failed to hatch as viable flies. Those which pupated after 16 August hatched as flies after a pupal stage of approximately 50 days and the first flies to hatch were invariably recovered during the first 2 weeks of October. The pupal stage decreased to approximately 25 days during December and January and increased again to approximately 50 days for flies hatching during May. No flies hatched between 18 May and 1 Cctober. The following life cycle ofr Oestrus ovis is suggested: sheep are repeatedly infested from October-June; thereafter infestation survives in the sheeps' heads until August, mainly as 1st instar larvae, then as pupae and larvae until fresh infestation takes place during October.     

Efficacy of a single whole-body spray treatment of spinosad, against Boophilus microplus (Acari: Ixodidae) on cattle.

The efficacy of a single whole-body spray of spinosad, a naturally derived control agent, applied at three concentrations was evaluated against cattle infested three separate times prior to treatment and at four weekly intervals following treatment with Boophilus microplus (Canestrini). At 0.0167% active ingredient (AI) both tick numbers (1894 ticks per calf) and index of fecundity (IF) of females (258.3) were no different than that of the control group. However, spinosad treatment at both 0.05 and 0.15% AI resulted in fewer ticks per calf (600 and 935, respectively) with lower IF values for females (43.4 and 38.4, respectively). The percent control of ticks on the animals at the time of treatment (acute efficacy) was dramatically lower at 0.0167% AI (21.4%) than at 0.05 (86.3%) and 0.15% AI (87.9%). Spinosad treatments appeared to be more effective against immature stages (nymphs and larvae) than against adult ticks that were on the animals at the time of treatment. The mean weight of females that survived to repletion was similar (322-348 mg) in all groups. By contrast, the mean weight of egg masses produced by females was highest in the control group (155 mg), whereas each increase in spinosad concentration resulted in a substantial decrease in egg mass weight, with the 0.15% AI group averaging only 73 mg. The hatch rate of eggs derived from females ranged from 93.4% in control females down to 53.9% hatch for females treated at 0.15% AI spinosad. The residual efficacy of spinosad at 0.0167% AI was poor even at 1 week following treatment, resulting in 101 ticks per calf and a level of control of only 66.4%. At 0.05% AI, protection against successful reinfestation was high at 1-week post-treatment where only five ticks per calf reached repletion, and control of the IF of these females was 99.3%. The 0.15% AI treatment provided almost complete protection against reinfestation for 2 weeks following treatment (< or =5 ticks per calf), and control of the IF of these ticks was >99.9%. Thus, the use of spinosad at US ports-of-entry would be unacceptable because of the critical necessity of achieving 100% control with a single treatment to prevent the reintroduction of ticks. However, it is likely ticks could be eradicated using spinosad in tick infested areas of the US if repeated (systematic) treatments were applied to cattle maintained on the premises.     

Seasonal dynamics and hosts of Amblyomma triste (Acari: Ixodidae) in Argentina

The seasonal dynamics and host usage of Amblyomma triste in Argentina were analyzed. Adults of A. triste were present from early winter to mid-summer, with the peak of abundance from late winter to mid-spring (August to October). Larvae and nymphs were found from December to June, with the peak of abundance in summer. There were no differences among the biological parameters (pre-moult period of larvae and nymphs, pre-oviposition period of females, and minimum incubation period of eggs) of engorged ticks exposed to different photoperiod regimens at the laboratory, but the periods for each biological parameter obtained from ticks exposed in the field were significantly longer than those from the laboratory. Field results fit better with the data of seasonal distribution of each stage. Morphogenetic diapause was not detected, but complementary studies should test the presence of behavioral diapause. Rodents of the subfamily Sigmodontinae (Akodon azarae, Oligoryzomys flavescens, Oligoryzomys nigripes, Oxymycterus rufus and Scapteromys aquaticus) are the principal hosts for immature stages of A. triste, the caviid Cavia aperea could be another potential host for these stages, and birds are exceptional hosts for larvae and nymphs. Regarding hosts of adults in Argentina, domestic and wild large-sized mammals belonging to different orders (cattle, dog, horse, Blastocerus dichotomus and Hydrochoerus hydrochaeris) serve as hosts for adults of this tick species. In conclusion, A. triste has a life cycle of 1 year with adults feeding on large endemic and introduced mammals and immature stages using sigmodontine and caviid rodents as hosts.     

Comparison of an amitraz-impregnated collar with topical administration of fipronil for prevention of experimental and natural infestations by the brown dog tick (Rhipicephalus sanguineus).

OBJECTIVE: To compare the efficacies of amitraz and fipronil for prevention of experimental and natural infestations of Rhipicephalus sanguineus. DESIGN: Prospective study. ANIMALS: 30 dogs. PROCEDURE: In 3 trials, dogs were allocated to 3 groups of 10 each. In trial 1, dogs were experimentally infested on day--1, and on day 0 were fitted with an amitraz-impregnated collar, treated topically with fipronil, or not treated. Ticks were counted daily until day 7, when viability of ticks and their progeny was determined. In trial 2, dogs were treated on day 0 and experimentally infested on days 7, 8, 10, and 13. Ticks were counted on days 8, 10, 13, and 18, and viability of ticks and their progeny was determined on day 18. In trial 3, dogs were exposed weekly to a tick-infested environment from day--3 to day 70. Dogs were treated on day 0, and ticks were counted and removed weekly from day 3 to day 77. RESULTS: Fipronil and amitraz were acaricidal and inhibited attachment and feeding. Amitraz had a significantly greater effect than fipronil on numbers of live, feeding ticks, egg hatchability, and larval viability, indicating partial ability to interrupt the tick life cycle. In field conditions, amitraz remained effective over the entire observation period. CLINICAL IMPLICATIONS: Amitraz had stronger and more sustained effects against tick infestation than fipronil.     

Parasites of domestic and wild animals in South Africa. XLV. Helminths of dairy calves on dry-land Kikuyu grass pastures in the Eastern Cape Province

Successive pairs of approximately 4-month-old Friesland bull calves, raised under worm-free conditions, were exposed to helminth infection for 14 days on dry-land Kikuyu grass pastures at 28-day to monthly intervals, on a coastal farm in a non-seasonal rainfall region of the Eastern Cape Province. With the exception of one pair of calves exposed for 28 days, this procedure was repeated for 28 consecutive months from December 1982 to March 1985. The day after removal from the pastures one calf of each pair was slaughtered and processed for helminth recovery and the other 21 days later. Both members of the last four pairs of calves were killed 21 days after removal from the pastures. Sixteen nematode species were recovered from the calves, and infection with Ostertagia ostertagi was the most intense and prevalent, followed by Cooperia oncophora. The calves acquired the greatest number of nematodes from the pastures from June to October of the first year and from June to August of the second year of the survey. Few worms were recovered from the tracer calves examined from November or December to March or April in each year of the survey. The seasonal patterns of infection with Cooperia spp., Haemonchus placei, Nematodirus helvetianus, Oesophagostomum spp., O. ostertagi and Trichostrongylus axei were all similar and were negatively correlated to atmospheric temperature and evaporation. Slight to moderate arrest in the development of fourth stage larvae occurred from July to September in Cooperia spp., April to July in H. placei, and August to October in O. ostertagi and Trichostrongylus spp. during the first year of the survey. Too few worms were present in the second year to determine a seasonal pattern of arrest. Species survival during the hot and windy summer months appeared to be achieved via a combination of arrested larval development and an ageing residual population of adult worms in the host, and a small extant population of infective larvae on the pastures.     

Development and survival ofhaemonchus contortus larvae on pasture in iraq

The survival of Haemonchus contortus infective larvae on pasture and soil was studied over a period of 12 months in the Baghdad area. Infective larvae were found on herbage and soil at all times except in the summer months. During autumn and winter infective larvae in pasture survived for periods of up to 32 weeks. Little larval migration into soil was observed during this study and larvae did not survive for long in the faecal pellets during the summer.     

黑绒金龟甲的发生规律研究

采用田间调查及室内饲养观察相结合的方法,研究了黑绒金龟甲(Serica orientalis)在兰州市的生活史、降水量对其田间消长动态的影响以及室内温度对其生长发育、卵孵化的影响。结果表明:25℃条件下,黑绒金龟甲的卵期6~9 d,幼虫3龄,幼虫期为53~86 d,蛹期9~16 d,成虫期长达9个多月,即280 d;黑绒金龟甲在兰州一年发生1代,4月下旬入蛰成虫开始出土,5月中旬~6月下旬成虫交配产卵;5月下旬~7月上旬为幼虫危害时期,7月中旬老熟幼虫开始转入地下化蛹,8月中旬蛹开始羽化,成虫当年不出土,在地下越冬,翌年4月下旬出蛰,黑绒金龟甲卵在18℃以下不能孵化,22~30℃时卵的历期随温度的升高逐渐缩短,32~35℃卵的历期则随温度的升高逐渐延长;其中,30℃时卵的孵化天数最短,为6.6 d;25℃时卵的孵化率最高,为95.00%,35℃时孵化率最低为21.25%。黑绒金龟甲的发生量与降水量有关,在每一个降水高峰期后,黑绒金龟甲的出土量明显增加。     

Efficacy of orally administered powdered aloe juice (Aloe ferox) against ticks on cattle and ticks and fleas on dogs

The efficacy of orally administered powdered aloe juice (Aloe ferox) was evaluated against ticks on cattle and against ticks and fleas on dogs. Twelve calves were each infested over a 25-day period with approximately 4000 larvae of Rhipicephalus (Boophilus) decoloratus and allocated to 3 groups of 4 calves each. Three days after the last larval infestation and daily for 22 days thereafter, the calves in 1 group were fed 5 mg/kg body weight and those in another 25 mg/kg body weight of powdered aloe juice incorporated in game maintenance pellets, while the animals in the 3rd group received only pellets. Detached female ticks were collected daily and counted and the weights and the fertility of groups of 50 engorged female ticks collected from the animals were ascertained. The powdered aloe juice in the game maintenance pellets had no effect on the tick burdens of the calves or on the fertility of the ticks. Six dogs, in each of 2 groups, were treated daily for 15 consecutive days, commencing on Day -5 before the 1st tick infestation, with either 0.39 g or 0.74 g of powdered aloe juice, administered orally in gelatin capsules, while a 3rd group of 6 dogs served as untreated controls. All the dogs were challenged with Haemaphysalis leachi on Days 0 and + 7, and with Ctenocephalides felis on Days + 1 and + 8, and efficacy assessments were made 1 day after flea and 2 days after tick challenge, respectively. Treatment was not effective against ticks or fleas on the dogs.     

The use of irradiated embryos of Chrysomya bezziana for the detection of the Old World screw-worm fly

Irradiation of Chrysomya bezziana embryos 1 h before hatching with doses less than or equal to 7 kilorad (kr) had a significant effect on percentage egg hatch, weights and survival of larvae. Doses greater than or equal to 1 kr allowed larval development to the end of the 3rd instar stage in vitro, but prevented normal pupal development. Cattle with wounds infested with 1st instar larvae derived from irradiated embryos had 3rd instar larvae present after 3 d but these failed to pupate. Thus it would be feasible to use such larvae for wound infestation for the enhanced detection of screw-worm fly in areas where the release of fertile flies is undesirable.     

Longevity of colonies of Anaplasma marginale in midgut epithelial cells of Dermacentor andersoni

Colonies of Anaplasma marginale in midgut epithelial cells of experimentally infected Dermacentor andersoni were studied in adult ticks 1, 3, and 6 months old. Longevity of the parasite in ticks was assessed by evaluating its infectivity for splenectomized calves; calves were exposed by feeding ticks and by inoculation of tick gut homogenates. Longevity was also evaluated by determining size, type, and density of colonies in male and female ticks. The effect of incubation (2.5 days at 37 C) on colony density was also examined for ticks at each age period. All methods used to assess longevity of A marginale in ticks (tick transmission, calf inoculation, and histologic studies) indicated a decrease of the numbers of organisms in 6-month-old ticks. Furthermore, when tick gut homogenates from 6-month-old nonincubated ticks were not infectious for susceptible calves, incubation of ticks before dissection restored infectivity of homogenates. Colonies of A marginale were detected in gut tissues of 6-month-old ticks that were not infective; therefore, infectivity of ticks could not be confirmed merely by presence of A marginale colonies.     

A note on the transmission of Babesia bovis (syn B argentina) by the one-host tick, Boophilus microplus.

Boophilus microplus infected with Babesia bovis were transferred artificially from one splenectomised calf to another during each moult in the parasitic life cycle of the tick. Eggs from the engorged female ticks recovered at the end of the cycle were incubated and the resulting larvae used to infest more splenectomised calves. Babesia bovis was transmitted only by the original larvae used at the commencement of the experiment and it was concluded that the protozoan parasite did not persist in an infective form in the ticks beyond the larval stage.