Ectoparasite fitness in auxiliary hosts: phylogenetic distance from a principal host matters.

We studied reproductive performance in two flea species (Parapulex chephrenis and Xenopsylla ramesis) exploiting either a principal or one of eight auxiliary host species. We predicted that fleas would produce more eggs and adult offspring when exploiting (i) a principal host than an auxiliary host and (ii) an auxiliary host phylogenetically close to a principal host than an auxiliary host phylogenetically distant from a principal host. In both flea species, egg production per female after one feeding and production of new imago after a timed period of an uninterrupted stay on a host differed significantly between host species. In general, egg and/or new imago production in fleas feeding on an auxiliary host was lower than in fleas feeding on the principal host, except for the auxiliary host that was the closest relative of the principal host. When all auxiliary host species were considered, we did not find any significant relationship between either egg or new imago production in fleas exploiting an auxiliary host and phylogenetic distance between this host and the principal host. However, when the analyses were restricted to auxiliary hosts belonging to the same family as the principal host (Muridae), new imago production (for P. chephrenis) or both egg and new imago production (for X. ramesis) in an auxiliary host decreased significantly with an increase in phylogenetic distance between the auxiliary and principal host. Our results demonstrated that a parasite achieves higher fitness in auxiliary hosts that are either the most closely related to or the most distant from its principal host. This may affect host associations of a parasite invading new areas.

Ticks associated with wild animals in the Nhecolândia Pantanal, Brazil.

A study of ticks associated with wild animals was carried out from September 1996 to April 1998 at the Fazenda Alegria (21,000 ha), in the Nhecolândia Pantanal, State of Mato Grosso do Sul, Brazil, a sunken plain bordering the upper Paraguay river, located 19 x 08'S; 56 x 46'W. A total of 81 wild animals (13 species, 6 orders) were captured with the aid of nets, and ticks were found on 63 (78%). Tick species identified included Boophilus microplus (Canestrini), Amblyomma cajennense (F.), A. parvum (Aragão), A pseudoconcolor (Aragão), A. scalpturatum (Neumann), A. nodosum (Neumann), A. ovale (Koch), and A. tigrinum (Koch). Dragging from grasslands (campos) yielded negative results compared to the high concentration of ticks, mainly nymphs, that were collected from leaves in the forests (capão). Predominance of immature instars (Amblyomma genera) was observed in the end of winter (August-September). Ticks were associated mainly with coatis, deer (Mazama gouazoubira) and anteater, and these animals may play a role in the epidemiology of tick-transmitted pathogens in the Pantanal if one considers their co-existence with local domestic animals.

Seasonal abundance of the tortoise tick Amblyomma marmoreum (Acari: Ixodidae) on the leopard tortoise, Geochelone paradalis.

A survey of Amblyomma marmoreum Koch ticks recorded from the leopard tortoise, Geochelone paradalis Bell, in the National Zoological Gardens, Pretoria, South Africa, was carried out over a 19-mo period. No significant differences were found between the tick burdens on male and female tortoises. A. marmoreum showed a clear seasonal pattern of abundance. Larvae were present on the tortoise host during late summer, with a peak in February and March; nymphs were abundant during winter, with a peak in June and July. Male ticks were found throughout the year, but females were present only during spring and early to midsummer with a peak in October. It was demonstrated that each developmental stage of A. marmoreum showed only one peak of activity per year.

Laboratory studies on the life cycle of Amblyomma marmoreum (Acari: Ixodidae) on two different hosts.

A comparative study was made of the life cycle of the tortoise tick, Amblyomma marmoreum Koch, on tortoises and guinea pigs under laboratory conditions. At 25 degrees C and 85% RH with natural day length, duration of off-host stages (preoviposition, oviposition, incubation, and premolt) was similar for ticks fed on both hosts. Delay in preoviposition (up to 90 d) was observed in some gravid females. Larvae, nymphs, and adults had longer feeding periods on tortoises than on guinea pigs. Adult females fed on tortoises had greater engorgement wieght and ovipositional capacity than ticks fed on guinea pigs. It is suggested that the shortened feeding period of immature stages on mammalian hosts together with the occurrence of morphogenic diapause may be more important than previously recognized in determining whether the life cycle of A. marmoreum is completed in 1 or 2 yr under natural conditions.

Evidence for attachment pheromones in the Cayenne tick (Acari:Ixodidae).

Evidence is presented for the existence of male-produced attachment pheromones in the tick Amblyomma cajennense (F). Unfed males and females attached significantly faster to shaved sides on bovine hosts where preattached males were present than did adult ticks released in control areas. Attached ticks did not form clusters around the preattached males as described for other species of Amblyomma. They attached in areas under bags where they had been released, but were not necessarily close to the feeding males. Males apparently required at least 4 d of feeding before producing the pheromones. Males that fed for < 3 d failed to induce attachment. A significant increase in attachment of newly introduced males and females was observed only on day 4 after the feeding of the preattached male started. This response increased on days 5 and 6 after feeding had commenced. An evolutionary trend in the production of tick pheromones was suggested.

Respiratory gas exchange in the flea Xenopsylla conformis (Siphonaptera: Pulicidae).

Respiratory gas exchange was measured in various developmental stages of the flea Xenopsylla conformis mycerini (Rothschild, 1904) originating from the central Negev in Israel. Gas exchange in fleas was measured using a flow-through respirometry system that monitored CO2 emission. Lowest metabolic rates were found in the cocooned stage, which included prepupae, early stage pupae, late stage pupae, and preemerged adults. Newly emerged adults and feeding larvae had metabolic rates 2.5-3.0 times greater than those for the cocooned stages. Highest rates of gas exchange were found in feeding fleas. The low metabolic rates of the cocooned stages is thought to contribute to their ability to survive for longer periods than free-living larvae and adults.

Production of pheromones by artificially fed males of the tick Amblyomma maculatum (Acari: Ixodidae).

Aggregation-attachment pheromones are produced only by male ticks of the genus Amblyomma that have imbibed blood for at least 8 d from their mammalian hosts. This report demonstrates that production and release of aggregation-attachment pheromones by Amblyomma maculatum (Koch) males can be induced in vitro by using nonblood media, artificially introduced through capillary tubes, into the male ticks. The presence of these pheromones is demonstrated by using both biological observations on bovine hosts and in vitro experimentation with petri dishes. The attraction of unfed female ticks to the artificially fed males (using the petri dish method) was significantly higher (P < 0.001) than the attraction of unfed females to unfed males. Similarly, attraction and attachment were recorded on bovine hosts. Only 62.8 +/- 17.5% of the females released attached to the bovine host. Of these, 61.9 +/- 19.37% attached around artificially fed males that were placed on the bovine 24 h earlier. This percentage did not differ significantly from the 81.4 +/- 7.1% of the total that attached around males that fed naturally for 8 d. In comparison, only 33.3 +/- 21.9% of the total number of females placed on the host did so after being fed 1 d (control group). The possibility of using capillary feeding as a new tool for investigating the physiology and reproductive behavior of blood-sucking arthropods is discussed.

Comparison of methods for introducing and producing artificial infection of ixodid ticks (Acari: Ixodidae) with Ehrlichia chaffeensis.

Only 29.5 +/- 8.91% of engorged Amblyomma americanum (L.) nymphs that we inoculated with Ehrlichia chaffeensis molted successfully to adults compared with 75.8 +/- 7.46% of engorged nymphs that were not inoculated. However, 65.4 +/- 6.02% of unfed nymphs of this species were exposed for 2 h to E. chaffeensis suspension introduced to them through glass capillaries gained weight. These nymphs were placed on rabbits, and approximately 50% of them completed their feeding and molted successfully to adults. Weight gained was higher (71.8 +/- 17.33% and 69.8 +/- 23.26%) for unfed A. americanum females that fed from capillaries for 2 and 24, h respectively, than for nymphs. Similar values were recorded for Dermacentor variabilis (Say) (61.0 +/- 16.23%) and Rhipicephalus sanguineus (Latreille) (59.0 +/- 18.62%) females after 24 h of capillary feeding. The amount of E. chaffeensis suspension taken in by females of A. americanum, D. variabilis, and R. sanguineus during 24 h of feeding was 11.2 +/- 3.56, 10.9 +/- 4.29 and 6.3 +/- 2.35 microliters, respectively. This volume is equivalent to approximately 12,969, 12,622, and 7,295 infected cells ingested by the species mentioned above. Positive correlation between the volume taken in by the ticks and the weight gained by the females was found, but the initial weight of the unfed females did not effect the weight they gained. The pathogen was found in the females of all 3 species by polymerase chain reaction procedures for at least 7 d, indicating that the capillary feeding method can be successfully used for infecting unfed ticks. The potential use of this method is discussed.

Respiratory gas exchange in the tick Amblyomma hebraeum (Acari: Ixodidae).

Respiratory gas exchange was studied in unfed adult Amblyomma hebraeum Koch. Carbon dioxide emission was measured at 25 degrees C using flow-through respirometry to determine standard metabolic rate and the temporal pattern of gaseous emission. The standard CO2 production rate (sVCO2) of inactive ticks was 0.0135 +/- 0.0085 ml g-1 h-1, and the standard O2 consumption rate (sVO2) was 0.0158 +/- 0.0097 ml g-1 h-1. Ventilation was discontinuous and was characterized by periodic bursts of CO2 emissions at frequencies of 0.33 h-1-1.11 h-1. Low metabolic rate coupled with discontinuous ventilation may contribute to the ability of adult A. hebraeum to withstand prolonged periods of starvation and desiccation in the absence of a host.

Effect of air temperature and humidity on the survival of pre-imaginal stages of two flea species (Siphonaptera: Pulicidae).

The survival of immatture fleas at 25 and 28 degrees C and 40, 55, 75, and 92% RH was studied to test the hypothesis that the difference in microclimatic preferences determines habitat distribution of Xenopsylla conformis Wagner, 1903 and Xenopsylla ramesis Rothschild, 1904. Survival of X. conformis eggs did not depend on either temperature or humidity or both, whereas eggs of X. ramesis survived significantly less at 40% RH than at higher humidities. No larva of either species survived at 40% RH at either temperature. Larval survival of both species at both temperature regimes was significantly lower at 55% humidity than at higher humidities. Maximal survival time of larvae that died before pupation depended on both temperature and humidity in both species. Change of humidity during early stages of the life cycle (from egg to larva) increased the maximal survival time in X. conformis larvae but decreased that in X. ramesis larvae. Pupal survival was higher at higher humidities independent of temperature. Survival of X. conformis pupae was lower than that of X. ramesis pupae when the relative humidity was low. Humidity change on later stages (from larva to cocoon) decreased X. conformis pupal survival and had no effect on X. ramesis pupal survival. The sex ratio of emerged adults was not affected by either temperature or humidity in both species. Changes in humidity between egg and larval emvironments significantly decreased the percentage of females in X. conformis emergence at 28 degrees C.

Isotopes as host blood markers to measure blood intake by feeding ticks (Acari: Ixodidae).

We have modified an experimental technique in which two different isotopes (Cr51 and I125) were used simultaneously as blood markers for determining the amount of blood removed by feeding ticks. This method enables us to measure separately and directly the volumes of red blood cells and plasma in ticks and to calculate the ratio between the two parameters (concentrating ability). The concentration of red blood cells in nymphs of Amblyomma hebraeum Kock and Rhipicephalus appendiculatus Neumann and in females of these species plus in those of Hyalomma truncatum Kock were found to be twice the amount measured in the labeled blood of goats. Concentrations of plasma in the ticks were approximately two-thirds of that measured in samples taken directly from these same goats. Small nonsignificant differences between the ability of various tick species to concentrate red blood cells and dilute host plasma were found. The advantage of this method is compared with that of the colorimetric and gravimetric methods, and its potential use is discussed.

Water uptake in the cat flea Ctenocephalides felis (Pulicidae: Siphonaptera).

To counteract water loss due to excretion, cuticular transpiration and respiration, various groups of arthropods have developed mechanisms for active uptake of water vapor from unsaturated air. In this study, active uptake capabilities and water loss rates were examined in the various developmental stages of the cat flea, Ctenocephalides felis. To determine critical equilibrium humidity, the lowest relative humidity at which active water uptake can occur, pre-desiccated immature and adult fleas were placed in a series of humidity regimes ranging from 44 to 93% RH. Active uptake occurred in larval stages at relative humidities above 53% and in pre-pupae at 75-93% RH. Pupae and adults did not demonstrate active uptake at any humidity. Optimal uptake for larvae occurred between 20 and 30 degrees C. When placed over Drierite (<10% RH), larval and adult stages demonstrated a higher rate of water loss than pre-pupal and pupal stages. Active water uptake is necessary to ensure proper development of the larvae of C. felis. Active uptake ceases after the larval-pupal ecdysis and it appears that adults have lost the ability to actively uptake water.

Time of survival under starvation in two flea species (Siphonaptera: Pulicidae) at different air temperatures and relative humidities.

We studied the effect of air temperature and RH on the survival time of adult Xenopsylla conformis Wagner, 1903 and Xenopsylla ramesis Rothschild, 1904 fleas during starvation to explain the paratopic habitat distribution of these species on opposite ends of a precipitation and temperature gradient in the Negev Highlands, Israel. We hypothesized that the pattern of distribution of the two flea species is caused by differential microclimatic preferences of imagoes and predicted that (1) the resistance to starvation would differ between the two flea species at different air temperatures (10 degrees C - 38 degrees C) and relative humidities (RH) (40%-92%) and (2) survival time of starving X conformis would be longer than that of starving X ramesis at high air temperatures and low RHs. Survival time of newly emerged X conformis was dependent on air temperature but not on RH, whereas in newly emerged X ramesis it was affected by both air temperature and RH. Generally, survival time of newly emerged fleas was longer at lower air temperatures and higher humidities than at higher air temperatures and lower humidities. No significant difference in survival time between species in dependence on either air temperature or RH were found for newly emerged fleas. Fed fleas of both species responded similarly to changes in air temperature and RH in terms of survival time. Survival time at lower temperatures was longer than that at higher temperatures. Females survived longer than males at all air temperatures except for the highest temperature when the survival time of both sexes was similarly low. In both species, the effect of RH on survival time was significant at the highest RH only, with a decrease in survival time at 92% RH. In contrast, survival times at lower RHs did not differ. Males of both species survived for less time than females at all RHs. X conformis generally survived for less time than X ramesis, all else being equal. The only regime at which X conformis survived longer than X. ramesis was 38 degrees C and 40% RH. Newly emerged fleas survived for significantly longer time than fed fleas.

Selected biochemical parameters in captive mountain tortoises (Geochelone pardalis).

The concentrations of sodium, potassium, chloride, urea, creatinine, uric acid, total protein, albumin, inorganic phosphorous, calcium, magnesium, cholesterol, triglyceride, glucose, aspartate and alanine transaminases (AST and ALT), creatine kinase (CK), lactic acid dehydrogenase (LD), gamma-glutamyltransferase (GGT), alkaline phosphatase (ALP) and total bilirubin in the serum of a captive population of the mountain tortoise (Geochelone pardalis) (n = 13) were determined. Results varied considerably, particularly for most enzymes such as AST (11-113 U/l,ALT (1-72 U/l), CK (12-242 U/l), LD (147-2641 U/l) and ALP (56-168 U/l).

The effect of host resistance on the metabolic rate of engorged females of Rhipicephalus evertsi evertsi.

This study investigated the effect of acquired resistance in guinea-pigs on the metabolic rate of adult females of the tick Rhipicephalus evertsi evertsi. Guinea-pigs were subjected to three successive infestations of ticks and the rate of CO2 production (VCO2) measured in first and third infestation engorged females. Ticks which fed on resistant hosts showed a 52% decrease in mass compared to ticks that fed on naive animals. Reduction in mass was accompanied by a decrease in VCO2 (mlh-1) per tick but an increase in mass specific VCO2 (mlg-1h-1). However, both groups shared a single allometric relationship between body mass and metabolic rate (VCO2). We suggest that the differences in size rather than any factor directly relating to the mechanism of acquired resistance account for the differences in metabolic rate between ticks fed on naive and resistant guinea-pigs.

The effect of various host species in the feeding performance of immature stages of the tick Hyalomma truncatum (Acari: Ixodidae).

In order to determine the effect of various hosts on the feeding performance of the tick Hyalomma truncatum, were used three mammalian species as hosts. Larvae and nymphs of H. truncatum were fed, under controlled laboratory conditions, on gerbils, guinea-pigs and rabbits. The larvae fed for 4.3 +/- 1.4 days on gerbils, 5.6 +/- 1.3 days on guinea-pigs and 4.7 +/- 1.2 days on rabbits. The mean weights of the larvae which fed in the rabbits, guinea-pigs and gerbils were 0.58 +/- 0.09, 0.46 +/- 0.04 and 0.45 +/- 0.04 mg, respectively. The feeding periods of the nymphs on gerbils, guinea-pigs and rabbits were 7.9 +/- 1.3 and 9.6 +/- 2.2 days respectively. The mean weights of the nymphs which fed on the gerbils, guinea-pigs and rabbits were 22.5 +/- 2.8, 19.7 +/- 1.3 and 15.8 +/- 1.4, respectively. Hyalomma truncatum demonstrated a life cycle of a three-host tick on gerbils and guinea-pigs and of a two-host tick on rabbits. The evolutionary advantage of a two-host cycle over a three-host cycle in metastriate ticks is discussed.

Survival of six species of African ticks in relation to saturation deficits.

The survival of unfed males and females of six species of African ticks was monitored at five different saturation deficits at constant temperature (25 degrees C). The survivorship curves for each species comprised a pre-mortality period, prior to when ticks started to die and a mortality period corresponding to a rapid increase in the mortality rate. Longevity was defined as pre-mortality plus mortality. A negative correlation between the longevity of the ticks and the saturation deficits was found with ticks surviving longer at lower deficits. The survival of males and females was similar. At low saturation deficits (2-4 mmHg) Amblyomma hebraeum survived the longest periods (74 weeks). Some correlation was found between the tick survival under dehydrating conditions and habitat associations. Rhipicephalus appendiculatus and Haemaphysalis leachii, the most mesic in distribution, had the shortest longevity (21 and 13 weeks, respectively) at high saturation deficits (7-21 mmHg). Hyalomma marginatum rufipes, the most xerophilic in distribution, had the longest survival (39.3 +/- 10.5 weeks) at high saturation deficits. Other factors apart from the adult survival should be taken into account when accounting for the tick distribution, in particular the tolerance of earlier developmental stages to desiccation.

The effects of tick numbers and intervals between infestations on the resistance acquired by guinea-pigs to adults of Rhipicephalus evertsi evertsi (Acari: Ixodidae).

Guinea-pigs were infested three times at short (1 week) intervals or long (10 week) intervals between successive infestations with low (1), medium (8) and high (15) numbers of adult Rhipicephalus evertsi evertsi. To compare the resistance developed by the hosts at short and long intervals between infestations, a challenge (fourth) infestation was performed with the high number of ticks. Resistance was assessed by comparing the mean weight of engorged female ticks that dropped from the hosts. Concentrations of beta globulins in the host sera were also monitored. Different tick loads (low, medium and high) and infestation intervals had a similar influence on the reduction in weight of the females which was between 60-70% after the final challenge. However, the concentration of beta globulins, was highest in the guinea-pigs exposed to medium and high numbers of ticks with long infestation intervals, probably because of an increase in the production of protective antibodies in response to more intensive antigenic challenge. The relationship between engorgement weight and beta globulin levels in host sera is discussed.

Acquired immunity to larvae of Amblyomma marmoreum and A.hebraeum by tortoises, guinea-pigs and guinea-fowl.

A study of acquired resistance in guinea-pigs, guinea-fowl and tortoises to larvae of the ticks Amblyomma hebraeum Koch and A.marmoreum Koch (Acari: Ixodidae) showed that repeated infestations of the laboratory host resulted in a 29.3-49.4% reduction respectively in weight of engorged larvae. No resistance was induced in guinea-fowl, the natural host for larvae of both species. A small decline in the mean weight of engorged larvae was observed for both species of ticks after three successive infestations on tortoises. The reduction in weight was more pronounced in A.hebraeum (14.5%) which does not naturally feed on tortoises than for A.marmoreum (8.4%), a common tick on this host. The occurrence of acquired resistance in natural tick host relationships as opposed to unnatural tick host relationships is discussed.

Water metabolism in the Namib Desert golden mole, Eremitalpa granti namibensis (Chrysochloridae).

1. Laboratory and field studies of energy and water metabolism employing isotopic dilution methods examined the ability of Namib Desert moles to survive on an insect diet without drinking water. 2. Water independence is achieved through efficient renal function while low rates of energy usage and torpor are further effective in reducing overall water requirements.