Unfed Adult Ticks Research Articles

Genetic diversity and the absence of regional differences of Borrelia garinii as demonstrated by ospA and ospB gene sequence analysis.

Unfed adult Ixodes persulcatus ticks were collected from four locations of Nagano and Hokkaido in Japan. Infected Borrelia garinii were investigated by PCR-RFLP of the ospA and ospB gene sequences. The primer set amplified an approximately 1.6-kb DNA fragment (0.7-kb in some strains), and BsrI, BstYI, or NlaIII digestion of the product resulted in six distinctively different PCR-RFLP groups and two independent borrelial strains. The representatives in each PCR-RFLP group and individuals from the borrelial strains were sequenced, and their deduced amino acid sequences were aligned. A neighbor-joining phylogenetic analysis showed that the B. garinii OspA or OspB sequences were each divided into three major clusters including isolates from both the Nagano and Hokkaido locations. There was no local difference in OspA/B sequences between Nagano and Hokkaido. The osp gene of Borrelia burgdorferi sensu lato is highly heterogeneous, and this was also confirmed by our sequence analysis. Some strains of the different PCR-RFLP groups had closely related OspA sequences, while the OspB sequences of these strains were quite different. These findings suggested intraspecies gene exchange and recombination events between the two genes in B. garinii.

Interaction between ticks (Acari: Ixodidae) and pathogenic nematodes (Nematoda): susceptibility of tick species at various developmental stages.

The virulence of entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) to tick species under laboratory conditions is reported. The susceptibility of larval, nymphal, and adult stages of the ticks Hyalomma excavatum (Koch), Rhipicephalus bursa (Canestrini & Fanz), and R. sanguineus (Latereille) to 2 strains of Steinernema carpocapsae and 3 strains of Heterorhabditis bacteriophora were compared in laboratory assays. Preimaginal stages of ticks were found to be more resistant to the nematodes than were adult ticks which exhibited 80-100% mortality in a dish containing 5,000 infective juveniles of H. bacteriophora IS-3 or IS-5 strains isolated in Israel. These 2 strains were found to be much more virulent to unfed adult ticks than were the other isolates. No marked difference was found between engorged ticks and unfed adults of R. sanguineus or H. excavatum in terms of mortality, whereas engorged males and unfed females of R. bursa were significantly more susceptible than unfed males or engorged females.

Mixed infection by tick-borne encephalitis virus and Borrelia in ticks.

To investigate the relationships between tick-borne encephalitis (TBE) virus and the bacterial spirochaete Borrelia burgdorferi sensu lato in vectors with mixed infections, unfed adult Ixodes persulcatus ticks were collected by flagging from vegetation in southern-taiga forests of the Pre-Urals region of Russia where both infections circulate sympatrically. Prevalences of TBE and Borrelia infections in a total of 4234 ticks were compared over 5 years. No significant differences were revealed between the prevalence of Borrelia infection in ticks with and without TBE virus (29.4+/-7.8% vs 23+/-3.6%), or between the prevalence of TBE virus infection in ticks with and without Borrelia (24.0+/-6.6% vs 18.4+/-3.4%). In ticks with mixed infection (40/689 = 5.8%), concentrations of TBE virus and Borrelia were not significantly correlated with one another. Field observations showed parallel trends in the prevalence of these pathogens in tick populations from year to year (1993-1997) indicating that, in I. persulcatus with mixed infection, Borrelia and TBE virus do not seem to interfere with each other and are apparently not involved in any antagonistic relationships.

Local variations in the distribution and prevalence of Borrelia burgdorferi sensu lato genomospecies in Ixodes ricinus ticks.

Unfed nymphal and adult Ixodes ricinus ticks were collected from five locations within the 10,000-ha Killarney National Park, Ireland. The distribution and prevalence of the genomospecies of Borrelia burgdorferi sensu lato in the ticks were investigated by PCR amplification of the intergenic spacer region between the 5S and 23S rRNA genes and by reverse line blotting with genomospecies-specific oligonucleotide probes. The prevalence of ticks infected with B. burgdorferi sensu lato was significantly variable between the five locations, ranging from 11.5 to 28.9%. Four genomospecies were identified as B. burgdorferi sensu stricto, Borrelia afzelii, Borrelia garinii, and VS116. Additionally, untypeable B. burgdorferi sensu lato genomospecies were identified in two nymphs. VS116 was the most prevalent of the genomospecies and was identified in 50% of the infected ticks. Prevalences of B. garinii and B. burgdorferi sensu stricto were similar (17 and 18%, respectively); however, significant differences were observed in the prevalence of these genomospecies in mixed infections (58.8 and 23.5%, respectively). Notably, the prevalence of B. afzelii was low, comprising 9.6 and 7.4%, respectively, of single and mixed infections. Significant variability was observed in the distribution and prevalence of B. burgdorferi sensu lato genomospecies between locations in the park, and the diversity and prevalence of B. burgdorferi sensu lato genomospecies was typically associated with woodland. The distributions of B. burgdorferi sensu lato genomospecies were similar in wooded areas and in areas bordering woodland, although the prevalence of B. burgdorferi sensu lato infection was typically reduced. Spatial distributions vegetation composition, and host cenosis of the habitats were identified as factors which may affect the distribution and prevalence of B. burgdorferi sensu lato genomospecies within the park.

九州本土域におけるマダニ相の調査

From April 1991 to July 1995,we surveyed by flagging the geological and vertical distributions of adult ticks, and also their seasonal occurrences in the Kyushu mainland, Japan. A total of 3,815 unfed adult ticks which were collected at 14 localities consisted of four genera and 13 species; Amblyomma testudinarium, Dermacentor taiwanensis, Haemaphysalis flava, H. longicornis, H. kitaokai, H. hystricis, H. megaspinosa, H. campanulata, H. formosensis, Ixodes ovatus, I. persulcatus, I. monospinosus and I. nipponensis. Tick fauna in the southern part of Kyushu was abundant in species and numbers; especially the genus Haemaphysalis tick was predominant while in the northern part it was relatively scarce. The genus Ixodes ticks including I. persulcatus, a typical northern species, were found around 800-1,300m above sea level in Kuju and Sobo Mountains. Mt. Kuju apparently is the southern limit for I. persulcatus distribution.

Microclimate-dependent survival of unfed adult Ixodes scapularis (Acari:Ixodidae) in nature: life cycle and study design implications.

Microclimate and other abiotic factors may be important in determining the survival of arthropod vectors, yet the impact of such variables rarely has received careful examination. The impacts of habitat, microclimate, and experimental confinement on survival rates of unfed adult blacklegged ticks, Ixodes scapularis Say, were studied in field enclosures in southcentral and northwestern Connecticut. At both locations, 2 enclosures were placed in each of 3 different habitats (field, forest canopy, and forest/field edge). Forty wild-caught adult ticks (20 males, 20 females) were placed in each enclosure. At one site, another 40 ticks were confined to nylon mesh bags placed inside each enclosure. Soil temperature, ground-level air temperature and relative humidity were measured within each habitat. The number of ticks surviving within each enclosure was monitored 1 or 2 times per week. Ticks that were confined in nylon bags had a lower survival rate than ticks that were able to move freely within the enclosures. Ticks survived longer in edge and forest habitats than in open fields, which were characterized by greater extremes in air temperature, soil temperature, relative humidity, and vapor pressure deficit than the other 2 habitats. The mean daily survival rates of free-ranging I. scapularis were negatively related to air temperature, vapor pressure deficit, and the coefficient of variation of relative humidity.

Cutaneous hypersensitivity induced in dogs and guinea-pigs by extracts of the tick Rhipicephalus sanguineus (Acari: Ixodidae).

The cutaneous hypersensitivity induced by Rhipicephalus sanguineus tick extract in dogs (natural host) and guinea-pigs (laboratory host) was evaluated. The left ear of infested and control (tick-bite naive) dogs and guinea-pigs was injected intradermally with an extract from unfed adult ticks and the right ear with phosphate buffered saline (PBS). Ear thickness variations were then measured after 10 min and 1, 2, 6, 18, 24, 48, 72 and 96 h post-injection. Results were expressed as percentual changes in the ear thickness in relation to pre-inoculation values. The final variation in ear thickness induced by the extract was given by subtracting, in each animal, the right ear percentual increase from that of the left ear. Guinea-pigs were tested at two different times following infestation and with two different doses of extract. Infested guinea-pigs from the three experiments developed an immediate (within the first 2 h post-inoculation) and a strong delayed reaction (24 h) to the extract. Dogs, unlike guinea-pigs, developed only a strong immediate reaction whereby an 80% increase in ear thickness was observed. Control animals, with the exception of one dog, did not develop any significant reaction to the extract. Only mild reactions were induced by PBS in the right ear of all animals. The correlation between the absence of a strong delayed type reaction to tick extract and the lack of resistance of the natural host to R. sanguineus tick is discussed.

Evidence for kairomonal influence on selection of host-ambushing sites by adult Ixodes scapularis (Acari: Ixodidae).

Unfed adult blacklegged ticks Ixodes scapularis Say, were tested under laboratory conditions for behavioral responses to substances rubbed from external glands on legs of white-tailed deer, Odocoileus virginianus (Zimmermann). In replicated trials, significantly more female ticks became stationary on portions of vertical glass tubing rubbed with the tarsal gland substances of both bucks and does than on nontreated tubing. This behavior, apparently an arrestant response, was infrequent among males. White-tailed deer urinate upon their tarsal glands, and doe urine also produced an arrestant response among female ticks. Metatarsal gland secretions of bucks elicited no arrestant response in either male or female I. scapularis, but doe metatarsal gland secretions elicited low-level positive responses from both sexes. A low-level arrestant response also was exhibited by females to secretions from the interdigital glands of bucks. In a second bioassay, three times as many females came to rest on the terminal ends of vertical glass rods whose bases were treated with secretions from buck interdigital glands than on rods with nontreated bases. This suggests that interdigital gland secretion influences blacklegged tick climbing behavior. Substances produced by or associated with the leg glands of O. virginianus may therefore serve as kairomones for host-seeking adult I. scapularis; interdigital gland secretions on soil or leaf litter may signal active deer trails, and tarsal gland substances may denote portions of vegetation contacted previously by white-tailed deer. In nature, use of these chemical cues by host-seeking adult I. scapularis may increase the probability of acquiring a suitable host.

Hyalomma truncatum (Acari; Ixodidae): investigations into the scototaxis of unfed adult ticks

Under controlled test conditions, unfed male and female Hyalomma truncatum ticks exhibited a positive scototaxis to stationary, two-dimensional targets. Upright-positioned rectangles were the most attractive targets. The attractiveness of these targets increased with their size. Significantly more ticks responded scototactically positively to the targets under a luminance contrast ratio of 5:1, as compared with other luminance contrast ratios. Targets with an elevation angle of 13 degrees were occupied more frequently than objects with higher elevation angles. Scototaxis was the same towards a stationary and a sinusoid oscillating target. When an upright-positioned rectangle was combined with a CO2 gradient, the number of ticks that migrated into the CO2 gradient and contacted the target did not increase significantly. The interval between exposure and first locomotion of the ticks, however, was significantly shorter under the influence of a CO2 gradient than in all other experiments without a CO2 gradient. A temperature gradient simulating a natural host (cattle) did not alter the scototaxis. The results of these investigations suggest that the positive scototaxis exhibited by adult H. truncatum ticks is not likely to be part of their appetence behaviour but rather searching behaviour to find adequate protection from harsh climatic conditions.

Oxygen consumption of engorged nymphs and unfed adults of Hyalomma asiaticum ticks (Acari: Ixodidae) exposed to various photoperiods.

The oxygen consumption of engorged nymphs of Hyalomma asiaticum was measured at various intervals after drop-off from mice hosts. Duration of nymphal development to the emergence of adults was 25-32 days at 25 degrees C. The oxygen consumption was high immediately after completing the blood meal (193-248 mm3 g-1 h-1 but decreased significantly 18 days later (at 25 degrees C) to 45-65 mm3 g-1 h-1. It increased again before ecdysis (81-102 mm3 g-1 h-1, and also after ecdysis in freshly moulted adults (177-220 mm3 g-1 h-1. The oxygen consumption in 8-month-old adult ticks was very variable ranging from 40-42 to 172 mm3 g-1 h-1. Neither engorged nymphs nor unfed adult ticks showed any dependence of their respiratory metabolism on the photoperiodic regimes tested (LD 20:4 and LD 12:12, with or without transfer to an alternative photoperiod after engorgement of nymphs).

Hyalomma truncatum and Rhipicephalus evertsi mimeticus (Ixodoidea, Ixodidae): reactions of adult ticks to vertically incident narrow- and wideband optical radiation with and without the influence of a CO2 gradient

Investigations concerning the reactions of unfed Hyalomma truncatum and Rhipicephalus evertsi mimeticus female and male ticks to vertically incident narrow- and wideband optical radiation at irradiances of 0.115 mWcm-2 and 0.98 mWcm-2, respectively, revealed that, independent of sex, adults of the two species are capable of perceiving a wide range of wavelengths. Considering the migration into the entry area of the optical radiation at the test chamber's ceiling as a positive phototaxis, H. truncatum always reacted with higher percentages than R. e. mimeticus. Compared to the controls, R. e. mimeticus ticks occupied the entry area of the optical radiation significantly more frequently only in the wavelength ranges of 415–474 nm, 529–628 nm, 611–707 nm and 190–2,600 nm, but always with low rates. High percentages of H. truncatum ticks, however, consistently reacted with a positive phototaxis in all the offered monochromatic sectors between 292–707 nm and also in the wide spectral range of 190–2,600 nm, particularly in the range of 470–520 nm. When ticks of both species were additionally confronted with a stable CO2 gradient, continuously increasing from 0.18 vol% at the bottom to 0.90 vol% at a height of 40 cm in the test chamber, they moved less frequently to the entry area of the optical radiation, compared to ticks tested without CO2, regardless of their exposure to darkness or to narrow- and wideband radiation. The percentages of ticks, however, that moved in a vertical direction, but did not reach the chamber's ceiling were always higher, with the exception of R. e. mimeticus at the wavelength range of 415–474 nm. A total of 30 unfed male and 30 unfed female adult ticks of both tick species were investigated at each combination of a narrow- and wideband spectral range, with and without the influence of a CO2 gradient. Considering moving ticks only, the interval between exposure and first movement of ticks was shorter under the influence of an additional CO2 gradient. The average delay in reaction with and without the stimulus of the CO2 gradient was 156.2 s and 195.6 s, respectively, for H. truncatum and 126.6 and 226.3 s, respectively, for R. e. mimeticus.

Antigen-capture enzyme-linked immunosorbent assay for detection and quantification of Crimean-Congo hemorrhagic fever virus in the tick, Hyalomma truncatum

A viral antigen-capture ELISA was compared to a viral plaque-assay on human cell monolayers for detection and quantification of Crimean-Congo hemorrhagic fever virus in triturated experimentally infected Hyalomma truncatum ticks. In suspensions of ticks exposed as larvae to viremic mice, the ELISA detected 13% positive as compared to 3% ( n = 721) positive by plaque-assay. Adult ticks inoculated with virus and sampled up to 102 days later were 84% positive by ELISA compared to 36% ( n = 273) positive by plaque-assay. The two tests detected similar proportions of positive ticks in the two weeks immediately after viral inoculation; however, the ELISA was positive in 100% of inoculated adult ticks from 18–102 days post-inoculation while the plaque-assay was positive in 33% ( n = 135) of the same specimens. CCHF viral antigen was detected in 10% ( n = 101) of first-generation progeny tested as unfed larva pools by ELISA, yet no virus was detected by plaque-assay, indicating that either non-infective viral fragments or very low levels of live virus were detected by ELISA in these tick progeny. As detected by plaque assay, virus inoculated unfed adult ticks were virtually all infected by day 8 post-inoculation; by day 21 post-inoculation only 33% were detected as positive. A cohort of these ticks were allowed to blood feed from day 21–31 post-inoculation. When assayed after feeding all female ticks and nearly 50% of male ticks were detected as virus-positive. This indicates that the virus likely persisted in the unfed ticks below the level of detectability of the plaque-assay and increased in the blood fed ticks up to a detectable level. The ELISA however, detected 100% of ticks as virus-positive from day 14 post-inoculation throughout the remainder of the study, regardless of feeding status (day 102 post-inoculation). These results indicate that antigen-detection ELISA is more sensitive in detecting CCHF virus in ticks than plaque-assay. Since an infected tick remains antigen-positive by ELISA for possibly the remainder of its life, this assay will be a major improvement in field surveys and vector competency studies of ticks for CCHF virus.

The identification of a shared immunogen present in the salivary glands and gut of ixodid and argasid ticks.

The identification of a 70-kDa immunogen present in salivary gland extracts of several ixodid species, namely Hyalomma truncatum (sweating-sickness-inducing (SS+) and non-inducing (SS-) strains), Hyalomma marginatum rufipes and Rhipicephalus evertsi evertsi, is reported. The immunogen was identified by Western blots using a monoclonal antibody of the IgM isotype directed against a 70-kDa immunogen present in the salivary glands of (SS-) female H. truncatum ticks. Cross-reactivity with the gut of unfed adult ixodid ticks, Amblyomma hebraeum, Rhipicephalus simus simus, R. evertsi evertsi, Rhipicentor nuttali, H.m. rufipes, and salivary glands of adult argasid species, Ornithodoros savignyi and Ornithodoros moubata, was demonstrated using ELISA.

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. II. Attachment stimulation

Nine known or potential components of the aggregation-attachment pheromone of the ticksAmblyomma hebraeum andA. variegatum were tested as attachment stimulants. Unfed adult male and female ticks were confined in linen bags on the ears of rabbits that had been treated with solutions of the test compounds; the numbers attached were recorded after 24 h. In both species, males attached more rapidly and more readily than females. InA. hebraeum, attachment of males was induced by eight compounds (benzaldehyde, benzyl alcohol, 2,6-dichlorophenol, heptadecane, 2-methyl propanoic acid, methyl salicylate, o-nitrophenol and salicylaldehyde) and attachment of females by six compounds (benzaldehyde, benzyl alcohol, 2,6-dichlorophenol, 2-methyl propanoic acid, o-nitrophenol and salicylaldehyde). InA. variegatum, attachment of males was induced by seven compounds (benzaldehyde, benzyl alcohol, 2,6-dichlorophenol, heptadecane, methyl salicylate, o-nitrophenol and salicyladeehyde) and attachment of females by two compounds (methyl salicylate and o-nitrophenol). A mixture of the nine compounds and extracts of prefed males ofA. herbraeum andA. variegatum induced attachment in males of both species and in femaleA. hebraeum; in these tests, attachment of femaleA. variegatum was only induced by extracts of conspecific males.

Effects of Juvenile Hormone and its Analogs on Vitellogenin Synthesis and Ovarian Development in Ornithodoros moubata (Acari: Argasidae)

Effects of juvenile hormones (JH) and JH analogs on the release of vitellogenin (Vg) into the hemolymph and ovarian development in unfed adult female ticks, Ornithodoros moubata (Murray), were investigated. Topical application of acetone solvent and injection of acetone or oils showed some increase in Vg titer in the hemolymph. Topical application of JH (JH I, JH II, JH III) and JH analogs (methoprene, S21149, S21150, and S31183) dissolved in acetone to unengorged adult females elevated Vg titer in the hemolymph but only to the same level as the acetone controls. These effects were independent of dose. Injection of JH (JH I, JH II, JH III) and methoprene dissolved in mineral oil also did not significantly increase the Vg titer in the hemolymph compared with the controls (mineral oil injection). Electrophoretic analysis of hemolymph from females 5 d after treatment topically or by injection with JH and JH analogs showed faint Vg bands which comigrated with Vg's (Vg-1 and Vg-2) of normal, engorged female hemolymph, but Vg bands were detected more clearly in the hemolymph samples that were collected greater than 2 wk after treatment. However, the same level of Vg also was detected in the hemolymph of females treated with acetone or mineral oil. Vg synthesis in females treated with JH and JH analogs was analyzed by in vivo labeling and fluorography, which showed that Vg synthesis was not induced by application of JH to unengorged females.

Investigation into the critical equilibrium humidity, active atmospheric water absorption and water content ofRhipicephalus evertsi mimeticus

The critical equilibrium humidity for fully engorged nymphs ofRhipicephalus evertsi mimeticus was shown to be between 91% and 93.5% r.h., and for adult male and female ticks to be between 82% and 84.5% r.h. Studies on gnathosoma and idiosoma by selective exposure to differing relative humidities have shown that dehydrated adult male and female ticks are capable of active uptake of atmospheric water vapor only through their mouthparts. The percentage of water content of unfed adult male and female ticks previously dehydrated was not influenced by subsequent exposure to different relative humidities, varying similarly in both sexes, male imagines between 59.6% and 63.7%, female imagines between 59.6% and 64.4%. Analogous values (62.3% and 61.1%) were obtained for the water content of male and female imagines not previously dehydrated, which were incubated at 30°C and 100% r.h. for 7 days.

Pheromone-mediation of host-selection in bont ticks (Amblyomma hebraeum koch).

The bont tick, Amblyomma hebraeum, is the principal vector to southern African ruminants of heartwater (Cowdria ruminantium infection). The role of feeding male ticks, which emit an aggregation-attachment pheromone, in attracting unfed ticks to cattle was investigated. Calves infested with feeding male ticks were more attractive to unfed adult ticks than were uninfested calves. The presence of the pheromone on previously infested cattle apparently allows unfed ticks to discriminate between hosts on which these parasites have fed successfully (suitable hosts) and those on which they have not (potentially unsuitable hosts). The use of acaricides is thus unlikely to reduce bont tick populations in areas where adequate numbers of alternate (wild) hosts are present. Also, cattle so treated may lose their resistance to heartwater through lessened exposure to infected ticks.

The establishment of infection in the salivary glands of Rhipicephalus appendiculatus ticks by transplantation of kinetes of Theileria parva and the potential use of the method for parasite cloning

Fujisaki K., Irvin A. D., Voigt W. P., Leitch B. L. and Morzaria S. P. 1988. The establishment of infection in the salivary glands of Rhipicephalus appendiculatus ticks by transplantation of kinetes of Theileria parva and the potential use of the method for parasite cloning. International Journal for Parasitology 18: 75–78. A simple method was developed to establish infection of a single salivary gland acinus of the tick Rhipicephalus appendiculatus with kinetes of Theileria parva. Kinetes were obtained from haemolymph of newly-moulted infected adult ticks and injected into the haemolymph of unfed adult ticks. The latter ticks were subsequently fed on rabbits; salivary glands were dissected out and acinar infection rates established. Transplantation of 16–138 kinetes into unfed female ticks resulted in infection of one or more salivary gland acini. Infection could not be reliably established in male ticks, nor in female ticks with fewer than 16 kinetes. The potential use of this method to obtain cloned populations of T. parva sporozoites is discussed.

Quantitative description of the development of Babesia ovis in Rhipicephalus bursa (hemolymph, ovary, eggs)

The development and infection dynamics of Babesia ovis in the hemolymph, ovaries, and eggs of Rhipicephalus bursa are described quantitatively, based mainly on examination of Giemsa-stained smears. After alimentary infection of female ticks, their hemolymph became infected 5 days after repletion (p.repl.). The prevalence and mean intensity of infection increased during the course of infection studied, up to 17 days p.repl. After vertical infection of female ticks, their hemolymph was infected only during the first 3 days after the onset of infestation (p. infest.) and again after the onset of alimentary infection 5 days p.repl. There was a positive correlation between prevalence and mean intensity of infection in the hemolymph. The prevalence of infection decreased with aging of the unfed adult ticks. After alimentary infection, the ovaries became infected 6 days p.repl., and after vertical infection, 3 days p. infest; they remained infected until the death of the tick. Ticks selected for susceptibility during 18 and 19 vertically infected generations were more susceptible than ticks in their first to third vertically infected generations or alimentarily infected ticks. Eggs deposited on day 1 of oviposition were noninfected after alimentary infection of the female tick. After vertical infection of the tick, even such eggs became infected; the infection, then, was detectable in eggs produced throughout the oviposition period regardless of the infection mode. Intense hemolymph infections induced an increase of egg degeneration and a decrease of total as well as infected egg production. There was a positive correlation between the number of deposited and infected eggs as well as between prevalence and mean intensity of infection in eggs.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of size on feeding and breeding performance of Rhipicephalus appendiculatus Neumann

A positive mean correlation was observed between engorged larval weight and unfed nymphal weight. Similarly, positive linear correlations were observed between engorged nymphal weight and unfed adult weight, between unfed female weight and engorged female weight and between engorged female weight and egg batch weight. Positive linear correlations were also observed between scutal length and weight of unfed adult ticks and between the duration of survival and unfed weight of adult ticks at both 43 and 85% r.h. and 28°C. At 43% r.h. and 28°C, small ticks lost water faster than larger ones. At 96% r.h. and 28°C the small ticks also gained water faster than larger ones. For the sizes tested, all the male ticks were comparable in their ability to fertilize normal females, but the smallest females were incapable of reproduction.