Attachment sites of the tick Amblyomma marmoreum on its tortoise host,Geochelone pardalis

Leopard tortoises (n=162) were collected over a period of 19 months at the National Zoological gardens, Pretoria, South Africa and the attachment sites of larvae, nymphs and adults of A. marmoreum monitored. Most of the larvae (80%) and nymphs (87%) were found on the anterior parts of the tortoise while adults (90%) were found mainly on the posterior regions of the host body. The immature stages were predominant in soft skinned areas protected by the carapace especially the neck and upper leg areas. Male and female ticks were most commonly found on the posterior armpit. posterior legs and the areas surrounding the base of the tail. Interstadial competition as a major factor influencing attachment site segregation is doubtful. Anterior attachment site selection of the immature stages is believed to result largely from ticks lying passively in wait and then climbing onto the host as it moves through the vegetation and the requirement for soft skinned and protected areas to allow for blood feeding. Adult females usually attach posteriorly in areas that allow them to fully engorge without being dislodged by mechanical disturbance, while males prefer to attach at sites where they are protected but still remain in close proximity to female pheromone signals.     

Orientation of the gopher tortoise, Gopherus polyphemus

Twenty-three gopher tortoises were released in an open field at least 8 km from their home burrows, and thirty-seven were tested in an arena which excluded all directional landmarks. Over half showed a statistically significant individual direction preference under each of these conditions. Directions chosen had no relation to the homeward direction and were widely divergent for individuals from the same geographic population. Comparing the preferred directions in the open field and in the arena indicates that landmarks may have a disruptive effect on orientation. The preferred headings of ten tortoises subjected to a 6-hr phase shift was about ninety degrees in the expected direction, indicating that this species is capable of sun-compass orientation.     

Distribution and molecular characterization of Wolbachia endosymbionts and filarial nematodes in Maryland populations of the lone star tick (Amblyomma americanum)

The lone star tick Amblyomma americanum is host to a wide diversity of endosymbiotic bacteria. We identified a novel Wolbachia symbiont infecting A. americanum. Multilocus sequence typing phylogenetically placed the endosymbiont in the increasingly diverse F supergroup. We assayed a total of 1031 ticks (119 females, 78 males and 834 nymphs in 89 pools) from 16 Maryland populations for infection. Infection frequencies in the natural populations were approximately 5% in females and <2% (minimum infection rate) in nymphs; infection was not detected in males. Infected populations were only observed in southern Maryland, suggesting the possibility that Wolbachia is currently invading Maryland A. americanum populations. Because F supergroup Wolbachia have been detected previously in filarial nematodes, tick samples were assayed for nematodes by PCR. Filarial nematodes were detected in 70% and 9% of Wolbachia-positive and Wolbachia-negative tick samples, respectively. While nematodes were more common in Wolbachia-positive tick samples, the lack of a strict infection concordance (Wolbachia-positive, nematode-negative and Wolbachia-negative, nematode-positive ticks) suggests that Wolbachia prevalence in ticks is not due to nematode infection. Supporting this hypothesis, phylogenetic analysis indicated that the nematodes were likely a novel species within the genus Acanthocheilonema, which has been previously shown to be Wolbachia-free.     

Multiple paternity and breeding system in the gopher tortoise, Gopherus polyphemus

Little is known about the reproductive behaviors and the actual outcomes of mating attempts in the gopher tortoise (Gopherus polyphemus). We examined the mating system and reproductive behaviors of a population of gopher tortoises in central Florida. Using microsatellite markers, we assigned fathers to the offspring of seven clutches and determined that multiple fathers were present in two of the seven clutches examined. We found that gopher tortoises exhibited a promiscuous mating system with larger males fertilizing the majority of clutches. The advantage of larger males over smaller males in fertilizing females may be a result of larger males winning access to females in aggressive bouts with other males or larger males may be more attractive to females. Clutches produced by larger females tended to be sired by a single male, whereas clutches of smaller females tended to be sired by multiple males.     

Seasonal occurrence of the bont tick (Amblyomma hebraeum) in the southern lowveld of Zimbabwe

The seasonal occurrence of the bont tickAmblyomma hebraeum was recorded over 2 years on 20 Brahman cattle held in a 240-ha paddock at Mbizi in southeastern Zimbabwe. The cattle were infested with all life cycle stages throughout the study period, and no clearly defined seasonal patterns were recorded. Males remained attached for up to about 6 months, and consequently accumulated on the cattle and outnumbered females considerably. The cattle did not acquire resistance toA. hebraeum and the abundance of the adults increased steadily over the 2 years of sampling. The occurrence of adults and nymphs on hosts appeared to be largely independent of weather, and these stages were active over the entire range of temperature and relative humidity recorded during the study period. It was concluded that unfed adults and nymphs are able to engage in host-seeking irrespective of weather conditions as they do not await hosts on the vegetation but emerge from protected microhabitats in response to specific stimuli from hosts, notably, carbon dioxide and the aggregation-attachment pheromone emitted by attached males. This behavior may explain the reported absence of a consistent pattern of seasonal occurrence ofA. hebraeum at different locations in southeastern Africa.     

Area-restricted search by the plains pocket gopher (Geomys bursarius) in tallgrass prairie habitat

Because pocket gophers have the high energetic cost of excavatingburrows and an inability to detect distant food items throughthe soil, I hypothesized that individuals within establishedburrow systems would use area-restricted search as a foragingstrategy. To examine this hypothesis I compared gopher foragingeffort over a 10-month period between areas in which overallplant densities were experimentally varied. Gophers expendedapproximately 50% of their foraging effort in areas with thehighest plant density, even though these made up only 33% ofthe available area in experimental plots. In large, griddedareas sampled for an entire season as well as in small areasin which gophers foraged for less than 1 week, gopher foragingeffort was related to the density of a single leguminous plantspecies, Psoralea argophylla. In small plots where this plantspecies was at high density, gophers created more tunnel branches,thereby intensifying their search effort. Thus, area-restrictedsearch appears to increase the rate of encounter with the patchilydistributed Psoralea plants.     

Ultrastructure of Haller's organ in the tick Amblyomma americanum (L.)

Summary Haller's organ on the tarsus of the tick Amblyomma americanum (L.) (Acarina: Ixodidae; nymphal stage) was studied by scanning and transmission electron microscopy. It consists of a distal bristle group, (the anterior pit), and a proximal capsule which encloses several sensilla. The seven sensilla of the anterior pit (A1–A7) are all thick-walled and multi-innervated (2–9 neurons), but at least three different types can be differentiated. Sensilla A1 and A2 possess large, plugged pores (>1000 Å) and are the only sensilla with branching dendrites. A3 and A5 are characterized by a spoke-wheel arrangement of the cuticle wall and very fine pores (100–200 Å) penetrating the spokes centrally; A4, A6, and A7 do not exhibit any pore system but a single opening at the bristle tip is assumed.The capsule contains seven thin-walled, blunt-tipped sensilla, and several non-sensory cuticular projections (pleomorphs). All of these sensilla possess large plugged pores in the cuticle wall and numerous dendritic branches of several neurons (3–5) in the lumen. Glandular openings were found inside the capsule; their significance is discussed.The fine structure of Haller's organ supports the functions postulated by Lees (1948), namely olfaction for the capsule and humidity reception (among others) for the anterior pit.This research was supported in part by the Office of Naval Research, and by NIH Training grant ES 00069. Paper no. 3459 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh.     

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.     

New member of the protein disulfide isomerase (PDI) family identified in Amblyomma variegatum tick

Ticks belonging to arthropoda are blood feeding, geographically widespread ectoparasites of mammals, reptiles and birds. Their saliva contains active substances that protect them from host immune attack and allow for transmission of various pathogens during the feeding process. Characterization of tick saliva components can therefore contribute to the development of effective methods for the control of tick-borne diseases.

Here we describe the identification and basic characterization of a gene encoding a 55 kDa protein found in the salivary glands (SG) of Amblyomma variegatum tick. Based on the primary structure and homology to the family of protein disulfide isomerases (PDI; EC 5.3.4.1) the gene was named AvPDI. The 1461 nt long AvPDI open reading frame codes for a 487 amino acid protein. In vitro expressed AvPDI was exclusively localized in the endoplasmic reticulum. RT-PCR and Western blot analysis revealed that AvPDI expression is not restricted to the SG of the tick. More detailed analysis on tissue slides from SG detected an AvPDI specific signal in granular cells of the acini type II and III. Finally, reductase activity of AvPDI was confirmed in an insulin assay. The structural and functional characteristics suggest that AvPDI is another member of the PDI protein family and represents the first more closely characterized PDI in the ticks.     

Host location by larvae of the reptile tick Amblyomma vikirri (Acari: Ixodidae)

The newly described tick Amblyomma vikirri has a narrow host range, being found mainly on the Australian lizard, Egernia stokesii and rarely on another lizard, Tiliqua rugosa. Both hosts are in the family Scincidae. Larvae of A. vikirri were as successful in locating E. stokesii as T. rugosa from a range of release distances between 20 and 120 mm from the host. Over this range the proportion of ticks which successfully located hosts declined and the time taken by successful ticks to locate hosts increased with increasing release distance. From 60 mm, larvae of A. vikirri located four other lizard species from the families Scincidae and Agamidae and two non-living targets as successfully as they did E. stokesii. The only evidence that there was any host specificity in the searching behaviour of larvae of A. vikirri was that A. vikirri larvae spent less time paused and questing when they were searching for E. stokesii than when they were searching for T. rugosa. Aponomma hydrosauri, a tick which commonly infests T. rugosa but not E. stokesii, spent less time paused and questing when it was searching for T. rugosa than when it was searching for E. stokesii. However, the results overall suggest that the narrow host range of A. vikirri cannot be explained by any ability of the larvae of that species to discriminate between their natural host and other reptile species.     

Regional specialization of the sperm membrane in the tick Amblyomma hebraeum koch (Acari: Ixodidae)

Summary The spermatozoon of Amblyomma hebraeum is about 200 m long and comprises: (1) a thick, club-shaped anterior part, about 20 m long bearing at its apex a tactile hemisphere, and (2) an elongated tail-like part, about 180 m long. The surface of the tactile hemisphere is covered by numerous bulbous expansions, attached to it by short stalks. The base of the hemisphere is surrounded by a fringe of thin motile processes; the remaining surface of the spermatozoon is covered with long cellular processes which run more or less parallel to one another.The membrane-associated particles found on the membrane beneath the cellular processes are regularly arranged as groups of parallel strands. The external surface of the so-called peripheral granules, as revealed by freeze-etching, is smooth with a very small number of particles. Internally the particles exhibit a regular hexagonal pattern which has not been observed, so far, on any other membrane of these sperm cells.The regional specialization of the spermatozoon surface membrane in relation to sperm motility is discussed. The results obtained indicate that processes of three types: (1) bulbous expansions, (2) motile processes, and (3) cellular processes are regional specializations, all engaged in aspects of sperm motility.The technical assistance of Mr. R. Haemmerle of Balzers Research Laboratories, Mrs. F. Seif and Miss C. Pugin, is gratefully acknowledged     

Divergent environmental preferences and areas of sympatry of tick species in the Amblyomma cajennense complex (Ixodidae)

Four species of Neotropical ticks, Amblyomma mixtum, Amblyomma cajennense, Amblyomma tonelliae and Amblyomma sculptum (formerly included in the catch-all name A. cajennense), have an allopatric distribution in much of their range, with areas of parapatry for at least two of them. We inferred the abiotic niches of these organisms using coefficients of a harmonic regression of the temperature and the Normalized Difference Vegetation Index (NDVI, reflecting plant stress) from remotely sensed data from MODIS satellites with 0.05° spatial resolution. Combinations of coefficients describing the phenology of these two variables pointed to divergent niche preferences, compatible with previous events of vicariance among the species. Amblyomma cajennense has been recorded in areas with small variations in temperature and NDVI. The remaining species were recorded in areas with large variations. The maximum environmental niche overlap was ∼73.6% between A. mixtum and A. cajennense and 73.5% between A. tonelliae and A. sculptum. Projecting these inferences on the geographical space revealed probable areas of sympatry or parapatry between A. mixtum and A. cajennense or between A. tonelliae and A. sculptum, the latter of which was confirmed with field collections. The A. sculptum distribution overlaps with that of A. tonelliae in northern Argentina and Paraguay; parapatry occurs at one extreme of the conditions occupied by both species. Compared with areas of allopatry, sites with both species had consistently lower temperatures, except for 10–12 weeks during the summer, and higher NDVI values throughout the year. We hypothesise that the overlap between A. tonelliae and A. sculptum resulted from secondary contact between populations, with A. sculptum adapting to sites with high water availability to balance high summer temperatures. Additional surveys of the areas of spatial overlap among these species are necessary to elucidate the forces driving their evolution and their adaptation to the environment.     

Distribution, habitat utilization and age structure of a suburban fox (Vulpes vulpes) population

The occurrence of wild foxes in suburbia is discussed. It is shown that in London breeding populations of foxes are found 5 km from the city centre, and in the last 3 years foxes have been recorded in the very centre of the city. The fox population in London is shown to be heavily dependent on residential habitats for both daytime harbourage and when selecting sites for natal earths. The fox population is unevenly distributed in London, with a marked clumping of the adult population during most of the year. The age structure of the population is presented, and these data are compared with data for other canid populations. Conclusions are drawn as to the effects of conventional control techniques on the age structure of a fox population.     

Perception of breath components by the tropical bont tick,Amblyomma variegatum Fabricius (Ixodidae)

Wall-pore olfactory sensilla located in the capsule of Haller's organ on the tarsus of Amblyomma variegatum ticks bear cells responding to vertebrate breath: one of these sensilla contains a CO2-excited receptor and a second sensillum has a CO2-inhibited receptor. Each of these antagonistic CO2-receptors, which display typical phasic-tonic responses, monitors a different CO2-concentration range. The CO2-inhibited receptor is very sensitive to small concentration changes between 0 and ca. 0.2%, but variations of 0.01% around ambient (ca. 0.04%) induce the strongest frequency modulation of this receptor. An increase of just 0.001-0.002% (10-20 ppm) above a zero CO2-level already inhibits this receptor. By contrast, the CO2-excited receptor is not so sensitive to small CO2 shifts around ambient, but best monitors changes in CO2 concentrations above 0.1%. This receptor is characterized by a steep dose-response curve and a fast inactivation even at high CO2-concentrations (greater than 2%). In a wind-tunnel, Amblyomma variegatum is activated from the resting state and attracted by CO2 concentrations of 0.04 to ca. 1%, which corresponds to the sensitivity range of its CO2-receptors. The task of perceiving the whole concentration range to which this tick is attracted would thus appear to be divided between two receptors, one sensitive to small changes around ambient and the other sensitive to the higher concentrations normally encountered when approaching a vertebrate host.