Comparison of the attachment rates of males of the ticksAmblyomma hebraeum andA. variegatum to cattle,sheep and rabbits in the absence of aggregation-attachment pheromone

Losses in domestic ruminants caused by heartwater (Cowdria ruminantium infection) in Zimbabwe and Mozambique are greater when the vector isAmblyomma hebraeum than when the vector isA. variegatum. It has been suggested that the epidemiology of the disease may be influenced by the rates at which unfed adults of these two tick species attach to uninfested hosts (i.e. in the absence of the male-produced aggregation-attachment pheromone [AAP]). In this study we confined unfed males ofA. hebraeum andA. variegatum on uninfested cattle, sheep and rabbits and recorded their attachment rates. Males of both species attached more rapidly on cattle than on sheep or rabbits. Males ofA. hebraeum attached more rapidly than males ofA. variegatum on all three host species. The differences in the attachment rates between the two species were much greater on sheep and rabbits than on cattle. The findings suggest that in the absence of AAP, pioneer males of both tick species may attach to cattle, and pioneer males ofA. hebraeum may also attach to sheep. The differences in the attachment rates ofA. hebraeum andA. variegatum provide a possible explanation for observed differences in the epidemiology of heartwater associated with these two vector species.     

Comparison of known and suspected pheromonal constituents in males of the African ticks,Amblyomma hebraeum Koch andAmblyomma variegatum (Fabricius)

Three low molecular weight compounds were found in hexane: diethyl ether extracts of fed males of the African ticks,Amblyomma variegatum (tropical bont tick) andA. hebraeum (bont tick), namely,o-nitrophenol, methyl salicylate and 2,6-dichlorophenol. These same compounds were also found in a rinse of fedA. variegatum males, but were absent or present in only trace amounts in a rinse of fedA. hebraeum males.o-Nitrophenol and methyl salicylate were present in much higher concentrations (i.e., amounts/tick) inA. variegatum than inA. hebraeum. 2,6-Dichlorophenol was also more abundant inA. variegatum than inA. hebraeum, but the differences were not as great as with the former two compounds. Extraction in hexane over a 3-week period revealed four additional compounds, benzaldehyde, benzyl alcohol, benzothiazole and nonanoic acid. The first three compounds were found in males of both species; nonanoic acid was found only inA. hebraeum males. Published reports consistently show strong attraction byo-nitrophenol and methyl salicylate for both sexes of the two bont tick species; 2,6-dichlorophenol and benzaldehyde have been reported to be attractive to both sexes ofA. hebraeum. The possible roles of these compounds, as well as others occasionally reported fromA. hebraeum andA. variegatum, as components of the aggregation/attachment pheromone or other pheromones is discussed.Supported by Cooperative Agreement No. AFR-0435A-00-9084-00 with the U.S. Agency for International Development to the Department of Infectious Diseases, College of Veterinary Medicine, University of Florida, Gainesville, FL.     

Resistance of indigenous African cattle to the tickAmblyomma hebraeum

Field collections ofAmblyomma hebraeum Koch adults from six breeds of cattle were conducted on two farms in the Northern Transvaal. The density ofA. hebraeum adults was highest on Simmentaler cows, followed by Santa gertrudis, Africaner, Bonsmara, Brahman and Nguni. Indigenous breeds, namely Nguni, Bonsmara and Africaner, have the highest level of resistance toA. hebraeum. The relationship between tick abundance and the high level of resistance found in the indigenous breeds is discussed.     

Evaluating the economic damage threshold for bont tick (Amblyomma hebraeum) control in Zimbabwe

Controlling ticks and tick-borne diseases by frequent applications of acaricides (e.g., dipping) is costly, and can leave treated livestock vulnerable to epizootics of tick-borne diseases should the system of applying acaricides break down. The concept of only applying acaricides on an infrequent (strategic) basis often relies on the target tick population displaying a seasonal cycle. However, as adult bont tick (Amblyomma hebraeum) infestations in Zimbabwe's lowveld do not have a strictly seasonal pattern of occurrence, it is recommended that tick control only be applied when bont tick infestations are equal to, or greater than, their economic damage threshold. The economic damage threshold is the minimum average weekly standard female tick burden sufficient to cause damage equal in dollar value to the costs of applying tick control. Assuming that each standard female tick represents a 10 gram weight loss, the economic damage threshold (standard female ticks/week) is equivalent to the ratio of the producer price of beef (liveweight equivalent): per head cost of dipping (Eqn (3)). To illustrate the application of the threshold methodology, it was assumed that the producer price of beef was Z$1.63/kg (U.S.$0.33/kg) and that tick control cost Z$0.29/hd/dip (U.S.$0.06/hd/dip). This gave a threshold of 18 standard female ticks/head/week. Using tick counts obtained from 20 Brahman cattle held at Mbizi in southeastern Zimbabwe, it was shown that for the 1988 calendar year there were only 32 weeks when the economic damage threshold was met or exceeded. This is substantially less that the 44 dippings per year that have been, until very recently, legally required in Zimbabwe. Sensitivity analysis showed that a 10% rise in the cost of dipping reduced to 23 (a 28% decrease) the number of weeks when tick burdens exceeded the economic damage threshold. By further assuming that an acaricide application and residual effects will cause a 3–5 week interval before the next application may be required, the number of weeks when the tick burden was equal to or greater than the threshold of 18 standard females/week fell to just 9–12 weeks. Three factors may cause an alteration in the economic damage threshold: i) tick burdens may cause damage to the udders; ii) secondary infestations (e.g., screw-worm) may cause economic damage; and iii) nutritional stress of the cattle may reduce the actual average per tick weight loss. Until further data becomes available, it is recommended that the economic damage threshold methodology be used as described here, and that farmers closely observe their herds during the suggested weekly tick sampling for udder damage and secondary infestations.     

A comparison of live and destructive sampling methods of determining the size of parasitic tick populations

The accuracy of a general and a specific method of collecting and counting ixodid ticks on live hosts was compared with that of a destructive technique which can only be applied to dead animals. Destructive sampling provided considerably more accurate results than either of the live sampling methods when applied to domestic goats (Capra hircus) and a duiker (Sylvicapra grimmia).The smaller the life stage and the tick species the less likely it is that it will be recovered by either of the live sampling techniques. Both live and destructive sampling yielded similar results for adultAmblyomma hebraeum, a large tick.A sub-sampling method, used to estimate larval numbers, was repeatable and an accurate predictor of population size for populations ranging from 50 to 1000 of unengorgedA. hebraeum larvae.     

An evaluation of strategic and threshold control measures against the Karoo paralysis tick,Ixodes rubicundus (Acari: Ixodidae) in South Africa

Paralysis caused by feeding female Ixodes rubicundus ticks is a major problem in large areas of South Africa. As the life cycle of the tick extends over a period of 2 years, it was hypothesized that strategic treatment of sheep with an acaricide over a 2 year period, timed to kill most engorging females, should markedly lower the biotic potential of the tick. Two flocks of sheep grazing in separate paddocks known to be infested with I. rubicundus were treated either strategically or on a threshold basis (i.e. only when tick challenge exceeded a predetermined critical level in terms of paralysis) for a 2 year period. The tick burdens of untreated control sheep running with the two flocks were monitored over a 4 year period and their seasonal dynamics determined. The times at which peak infestations occurred were similar for both flocks of sheep, but significant differences in mean tick burdens between the two flocks were recorded. Tick numbers on sheep in the strategically treated flock did not decrease during the third and fourth years of the trial as was expected. Possible reasons for this were low stocking densities, especially during times of peak abundance of adults and the presence of wild hosts which maintained tick populations.     

Ecology and phenology of ticks in Zambia: Seasonal dynamics on cattle

A study of the seasonality and infestation rates of ticks was carried out in 11 cattle herds in different ecological habitats in Zambia between 1980 and 1982. Wherever possible supplementary data were obtained from opportunistic collections from cattle and other hosts.Analysis of over 1000 tick collections from cattle indicated that infestation rates of the most important species,Amblyomma variegatum andRhipicephalus appendiculatus vary in different ecological habitats: (i) In Western Province, infestations are much lower than elsewhere; (ii) in Central and Southern Provinces, moderate to high infestations occur; and (iii) in Eastern Province,R. appendiculatus numbers are generally low andA. variegatum numbers are moderate.These two species, however, have similar life cycles throughout their range with one generation per year. Larvae occur mainly from March to May, nymphae from May to September, and adults ofA. variegatum from October to December and ofR. appendiculatus from December to April. Boophilus decoloratus appears to have two to four generations per year but is uncommon during the rainy season. In some areas in central ZambiaRhipicephalus compositus adults are seasonally common in September–October whereasRhipicephalus evertsi is more or less ubiquitous. Low to moderate infestations ofHyalomma truncatum andHyalomma rufipes occur in most areas.At least 14 other less common or rare species ofRhipicephalus, Amblyomma, Haemaphysalis andIxodes were taken infrequently from cattle. These and other host-specific species were also collected from dogs, sheep, various wildlife hosts and the environment.Infestation rates, seasonality and host-relationship of tick species are discussed in relation to their ecology. Relevant biosystematic and disease relationships are reviewed briefly. The baseline data derived from this study are adequate for integrated analysis with those from other ecological and economic investigations to formulate tick control strategies.     

Specificity and effects of host resistance on the African tickRhipicephalus zambeziensis (Acarina: Ixodidae)

Repeated infestations of the rabbit with adultRhipicephalus zambeziensis ticks resulted in a tenfold reduction in engorgement weight of adult ticks and a significant decline in engorgement weight of nymphs. There was no evidence of cross-resistance against the South African bont tick,Amblyomma hebraeum. Immunization of rabbits with crude extracts of whole-tick protein significantly influenced engorgement weights and oviposition rates of adultR. zambeziensis.Histological studies of tissues fromR. zambeziensis adults fed on resistant rabbits showed severe gut damage; this was associated with the binding of host IgG to mid-gut cells.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. III. Aggregation

Ten known or potential components of the aggregation-attachment pheromone (AAP) of the ticksAmblyomma hebraeum andA. variegatum, as well as mixtures of these components, extracts of prefed males and live prefed males, were tested as aggregation stimulants. In field assays, laboratory-reared unfed male and female ticks were released 20 cm downwind of CO₂/pheromone release sites; the numbers of ticks that aggregated at the release sites were recorded after 30 min. InA. variegatum, aggregation was induced by methyl salicylate,o-nitrophenol, 2,6-dichlorophenol, phenylacetaldehyde and some mixtures containing these compounds; a strong aggregation response was induced by an extract of five prefed malesA. variegatum and a weak response was induced by an extract of 50 prefed males ofA. hebraeum. InA. hebraeum, aggregation was induced by phenylacetaldehyde, mixtures of compounds that included phenylacetaldehyde, extracts of 50 prefed males ofA. hebraeum orA. variegatum and 50 live prefed males ofA. hebraeum. InA. variegatum, aggregation was inhibited if compounds that do not occur naturally in the AAP of the species were included in mixtures. InA. hebraeum, phenylacetaldehyde appeared to act as an arrestant for ticks that had been attracted to release sites by other compounds.     

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.     

Factors affecting the distributions of the ticks Amblyomma hebraeum and A. variegatum in Zimbabwe: implications of reduced acaricide usage

The ticks Amblyomma hebraeum and A. variegatum are the main vectors of heartwater, a disease of ruminants caused by Cowdria ruminantium, in the agricultural areas of Zimbabwe. At present, A. hebraeum is widely distributed in the dry southern lowveld, and occurs in at least seven foci in the higher rainfall highveld. Amblyomma variegatum occurs in the Zambezi valley and surrounding dry lowveld areas in the northwest. The distribution of A. hebraeum has changed considerably over the past 70 years, while that of A. variegatum appears to have remained fairly static. The distribution patterns of both species in Zimbabwe display anomalous features; the ticks occur in areas of lowest predicted climatic suitability for survival and development and in areas where the densities of cattle, the most important domestic host, are lowest. The only factor favouring the survival of the species in the lowveld habitats in which they occur is the presence of alternative wildlife hosts for the adult stage. Their absence from more climatically favourable highveld habitats appears to have been the result of intensive acaricide treatment of cattle over a long period and a historic absence of significant numbers of wildlife hosts. Eradication of A. hebraeum and A. variegatum by intensive acaricide treatment of cattle can be achieved in the absence of significant numbers of alternative hosts, because of the long attachment and feeding periods of the adults of these tick species. However, eradication becomes impossible when alternative hosts for the adult stage are present, because a pheromone emitted by attached males attracts the unfed nymphal and adult stages to infested hosts. The unfed ticks are not attracted to uninfested hosts, such as acaricide-treated cattle.Regular acaricide treatment of cattle is expensive and so, for economic reasons, the Government of Zimbabwe is no longer enforcing a policy of strict tick control. It is likely that reduced tick control will result in the spread of Amblyomma ticks to previously uninfested areas. Added to this, recent introductions of various wildlife species to highveld commercial farming areas have created conditions in which the ticks could become established in higher rainfall areas. Amblyomma hebraeum is more likely to spread than A. variegatum, because its adults parasitize a wider range of wildlife hosts (warthogs, medium to large-sized antelope, giraffe, buffalo and rhinoceros), whereas adults of A. variegatum appear to be largely restricted to one wildlife species (buffalo) in Zimbabwe, the distribution of which is now confined to very limited areas of the country, as part of foot and mouth disease control measures. A model to predict the rate of spread of A. hebraeum through the highveld is described.Possible control options for dealing with the spread of Amblyomma ticks and heartwater to previous unaffected highveld areas, include (1) continuation of intensive acaricide treatment of cattle to prevent the spread, (2) establishment of a buffer zone of intensive tick control around affected areas to contain the spread and (3) allow the spread to occur and control heartwater by means of immunization. An economic analysis to determine the costs and benefits of the control options, which takes into account the development of Amblyomma-specific tick control technologies and improved heartwater vaccines, is recommended.Deceased.     

Responses of the ticksAmblyomma hebraeum andA. variegatum to known or potential components of the aggregation-attachment pheromone. I. Long-range attraction

Nine known or potential components of the aggregation-attachment pheromone of the ticksAmblyomma hebraeum andA. variegatum were tested as long-range attractants. In field assays, laboratory-reared unfed male and female ticks were released 4 m downwind of treated filter-paper targets. Carbon dioxide was used to activate the ticks and the numbers attracted to the targets were recorded. Adults ofA. hebraeum were attracted to six compounds (benzaldehyde, 2,6-dichlorophenol, heptadecane, methyl salicylate, nonanoic acid and o-nitrophenol) and adults ofA. variegatum to four compounds (2,6-dichlorophenol, methyl salicylate, nonanoic acid and o-nitrophenol). The most important attractant forA. hebraeum was o-nitrophenol; methyl salicylate and o-nitrophenol were the most important attractants forA. variegatum. Nonanoic acid and o-nitrophenol attracted significantly more female than maleA. hebraeum. Both species were also attracted by a mixture of the nine compounds.     

Monitoring of naturally acquired and artificially induced immunity toAmblyomma variegatum andRhipicephalus appendiculatus ticks under field and laboratory conditions

The ability of rabbits, goats and cattle to acquire immunity to the ixodid ticksAmblyomma variegatum andRhipicephalus appendiculatus was studied under laboratory and field conditions. Rabbits were successfully immunized with crude salivary gland extract (SGE) and midgut extract (ME) obtained from flat or partly fed femaleR. appendiculatus ticks. The lowest numbers of larvae were produced by females fed on rabbits immunized with unfed midgut extract. Similar reductions in larval production could be induced after three infestations of rabbits with adultR. appendiculatus. Also, successive feedings of nymphs ofR. appendiculatus on rabbits resulted in significantly reduced engorgement weights. Skin testing with SGE induced delayed-type hypersensitivity reactions, which could be correlated with immunity toR. appendiculatus in rabbits. Moreover, circulating antibodies were detected in rabbits with an ELISA using SGE ofR. appendiculatus.Immunity toA. variegatum nymphs could be induced in rabbits by repeated infestations, but this failed in goats. Immunization of goats with midgut extract from adultA. variegatum did not protect against subsequent nymphal challenge, but strong skin reactions were noticed when adults ticks fed on immunized goats. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of SGE and ME fromA. variegatum revealed the presence of 48 protein bands in SGE and 29 bands in midgut extract. Western blotting employing serum from a rabbit immune toR. appendiculatus recognized a number of bands in SGE fromR. appendiculatus, but also in SGE ofA. variegatum.Immunity acquired by cattle to ixodid tick infestations under field conditions was monitored by skin testing with SGE and western blot analysis. In general, cattle with the lowest tick numbers manifested the strongest delayed-type hypersensitivity responses. Finally, western blot analysis employing sera from tick-infested and tick-naive cattle could not be related to actual immune status.     

Using between-model comparisons to fine-tune linear models of species ranges

Aim To offer an objective approach to some of the problems associated with the development of logistic regression models: how to compare different models, determination of sample size adequacy, the influence of the ratio of positive to negative cells on model accuracy, and the appropriate scale at which the hypothesis of a non‐random distribution should be tested. Location Test data were taken from Southern Africa. Methods The approach relies mainly on the use of the AUC (Area under the Curve) statistic, based on ROC (threshold Receiver Operating Characteristic) plots, for between‐model comparisons. Data for the distribution of the bont tick Amblyomma hebraeum Koch (Acari: Ixodidae) are used to illustrate the methods. Results Methods for the estimation of minimum sample sizes and more accurate hypothesis‐testing are outlined. Logistic regression is robust to the assumption that uncollected cells can be scored as negative, provided that the sample size of cells scored as positive is adequate. The variation in temperature and rainfall at localities where A. hebraeum has been collected is significantly lower than expected from a random sample of points across the data set, suggesting that within‐site variation may be an important determinant of its distribution. Main conclusions Between‐model comparisons relying on AUCs can be used to enhance objectivity in the development and refinement of logistic regression models. Both between‐site and within‐site variability should be considered as potentially important factors determining species distributions.     

Tick prevalence and species diversity on Aldabran giant tortoises (Dipsochelys dussumieri) in relation to host range and host size in a restored ecosystem, Kenya

Tick species density and diversity on Aldabran tortoises was investigated in relation to the habitat range and size of each tortoise. Identification of tick infestation patterns forms an important aspect of effective tick control. Ten Aldabran tortoises were de‐ticked and monitored over the course of 2 months. Tick species found were Amblyomma sparsum, Amblyomma nuttalli, Amblyomma hebraeum and Boophilus decoloratus, with the most prevalent species found being A. sparsum. Tick loads varied considerably from 20 to 214 ticks per tortoise, with most ticks collected from the head/neck region. Tortoises ranging outside Haller Park had higher tick loads (70–214) compared with tortoises ranging within Haller Park (20–99). Tick load was not correlated with tortoise size. Results indicate that tick loads are related to the habitat range of the tortoises and may indirectly also be related to food preference and host food availability. Implications of the findings and appropriate tick control measures are discussed.     

Linking weather conditions and winter tick abundance in moose

Climate change may modify species distribution to higher latitudes, resulting in potential changes of parasite diversity and transmission dynamics in areas where animals might not be locally adapted to these new parasite species. In addition, climate change may increase the frequency and severity of infestations of parasites that are already present in a region, by promoting the development and survival of infectious stages. Over the last decades, the number of moose (Alces americanus) infested by winter ticks (Dermacentor albipictus) has increased in eastern Canada, possibly because milder climatic conditions are increasing winter tick survival. Our main objective was to determine which meteorological variables are more likely to influence winter tick load on moose. We compiled several weather variables that may limit winter tick survival and explored which weather variables, or their interactions, influenced the winter tick load of 4,100 hunted moose from 2013 to 2019 in Québec, Canada along a latitudinal gradient. Winter tick load in fall decreased with the maximum number of consecutive days in spring with average daily temperatures below −15°C and with the number of consecutive days in summer with a relative humidity <80% when snowmelt in spring was earlier. These results suggest that cold temperatures and prolonged periods of low humidity, amplified by early snowmelt, limit the survival of adult female ticks and eggs, thus limiting their subsequent load on moose during the following fall. With climate change, precipitation increases and warm temperatures occur earlier in spring and are more frequent in summer. Our results suggest that climate change may have a positive long-term influence on winter tick abundance in the environment and thereby increase winter tick load on moose, which could lead to a significant decrease in moose body condition and survival.     

A comparison of the attraction of nymphs and adults of the ticksAmblyomma hebraeum andA. variegatum to carbon dioxide and the male-produced aggregation-attachment pheromone

The attraction of nymphs of the ticksAmblyomma hebraeum andA. variegatum to CO₂ alone and CO₂ together with the male-produced aggregation-attachment pheromone (AAP) was investigated. Matching experiments on the attraction of the adults of the two species were run for comparison. Nymphs ofA. hebraeum were strongly attracted to sources of CO₂ and CO₂/AAP at distances of 10 and 15 m. At distances of 20 and 25 m significantly more nymphs were attracted to CO₂/AAP than to CO₂ alone. Adults ofA. hebraeum were not attracted to CO₂ alone at any distance; these ticks were attracted to CO₂ and AAP together for distances of up to 25 m. The patterns of attraction of nymphs and adults ofA. variegatum at 10 m were similar to those recorded inA. hebraeum.     

The effect of rainfall on tick challenge at Kyle Recreational Park,Zimbabwe

The effect of rainfall pattern on tick challenge was investigated at Kyle Recreational Park, Zimbabwe, from 1991 to 1992 using drag and removal plot methods to sample environmental tick density. The abundance of adults and nymphs of the brown ear-tick Rhipicephalus appendiculatus and larvae of the bont tick Amblyomma hebraeum was positively correlated with monthly rainfall, whereas no relationship with rainfall was revealed for larval R. appendiculatus, adults of the red-legged tick R. evertsi, or larvae of the blue tick Boophilus decoloratus. A comparison between 1991 (490 mm rainfall) and the drought year of 1992 (161 mm) revealed significant differences in the abundance of R. appendiculatus, A. hebraeum, and B. decoloratus. During the wet season, R. appendiculatus adults were 2–3 time more numerous in the environment during the higher rainfall year of 1991. A. hebraeum larval abundance exhibited a similar pattern to that of R. appendiculatus adults, but B. decoloratus larvae were more abundant in the drought year of 1992 during both the wet and dry seasons. Comparable tick abundance data collected at Kyle during the above-average rainfall years of 1975–1977 (mean = 1029 mm) were compared with tick challenge during the below-average rainfall years of 1991–1992 (mean = 326 mm). In grassland sand habitat and all habitats combined R. appendiculatus adults, nymphs, and larvae were much more abundant during the high rainfall years. In contrast, larvae of B. decoloratus were more numerous during the drier years. A. hebraeum larvae were also more abundant during the drier years. The strong positive correlation of adult R. appendiculatus abundance with rainfall and the coincidence of increased adult tick challenge with increased rainfall indicates that adult R. appendiculatus tick burden on hosts would be heaviest during the wet season and high rainfall years.     

Use of carbon dioxide and natural or synthetic aggregation-attachment pheromone of the bont tick,Amblyomma hebraeum,to attract and trap unfed adults in the field

It was determined previously that unfed adults ofAmblyomma hebraeum become active in response to carbon dioxide but are not attracted by it. We have now shown in field experiments that males and females which are activated by carbon dioxide are attracted to the aggregation-attachment pheromone produced by males after a period of feeding on the host. Unfed adults were attracted too-nitrophenol, a component of the aggregation-attachment pheromone ofAmblyomma variegatum, pre-fed males ofA. hebraeum, and extracts of such males. Live males were more attractive than the extracts which, in turn, were more attractive thano-nitrophenol. The ticks were attracted to sources ofo-nitrophenol from as far away as 11 m in 90 min. Simple traps, baited with carbon dioxide and aggregation-attachment pheromone (from pre-fed males or extracts of pre-fed males), were used to capture unfed adults that had been released in the field. The response of unfed adults to carbon dioxide and the aggregation-attachment pheromone presents an obvious host-location mechanism and a means for the ticks to discriminate between suitable hosts (those with males already attached) and potentially unsuitable hosts (those with no males attached).     

An update on the ecological distribution of Ixodid ticks infesting cattle in Rwanda: countrywide cross-sectional survey in the wet and the dry season

As part of the epidemiological studies aimed at developing an East Coast fever (ECF) immunisation control strategy, which combines an infection and treatment method with strategic tick control, a countrywide tick survey was carried out in both the dry and the wet season to determine the abundance and the dynamics of the tick populations infesting cattle in Rwanda. Six Ixodid tick species where identified from a total of 12,814 tick specimens collected. Rhipicephalus appendiculatus, the main vector of ECF was the most abundant (91.8%) followed by Boophilus decoloratus (6.1%) and Ambyomma variegatum (1.2%). Few ticks from the three other less economically important Ixodid species (Rhipicephalus compositus, R. evertsi evertsi and Ixodes cavipalpus) were recovered. Both adult and immature stages of the most dominant tick species were found to be widespread with a year round presence. The numbers of ticks were high in low land and medium zones and declined markedly in the higher regions of Rwanda. The geographical distribution of various tick species throughout the country and their epidemiological implications are discussed.