A new species of Ixodes (Acari: Ixodidae) from South African mammals

A new tick species belonging to the African subgenus Afrixodes Morel, 1966, namely, Ixodes ( Afrixodes ) fynbosensis n. sp., is described. The female of I. fynbosensis is easily differentiated from the other African Ixodes species by a large, tapering triangular ventrolateral spur on palpal segment I. Nymph and larva of I. fynbosensis can be distinguished from those of other members of Afrixodes by a combination of the following characters: pointed hypostome, long auriculae, long and acute ventrolateral projections of basis capituli of nymph, only 2 pairs of central dorsal setae, and a straight posterior margin of scutum of the larva. Cytochrome oxidase I mtDNA sequence comparisons between I. fynbosensis and 10 other Ixodes Latreille, 1795, species support the recognition of this taxon as genetically distinct (>13% corrected sequence divergences separate it from the remainder of the 10 recognized species used in this study), and preliminary phylogenetic analyses reveal that this taxon is most closely related to the southern African Ixodes pilosus Koch, 1844, and Ixodes rubicundus Neumann, 1904. Ixodes fynbosensis is known only from South Africa, where females have been collected from a domestic dog and a rodent, Rhabdomys pumilio (Sparrman), and nymphs and larvae have been collected from R. pumilio and unidentified shrews belonging to the Soricidae. Sequences generated for both nymphs and adult individuals were identical, confirming the correlation between the described life stages.     

Questing behaviour of Ixodes ricinus ticks (Acari: Ixodidae)

The vertical distribution in the vegetation of questing Ixodes ricinus ticks was investigated in two different vegetation types (high and low vegetation) at two localities in south-central Sweden during 1992-1993 (Toro) and 1995 (Bogesund). Significant correlations were found between the vertical distribution of immature ticks and the height of the vegetation. The greatest mean availabilities of the larvae and nymphs in low vegetation were in the intervals 0-9 and 30-39 cm, respectively. The larval numbers were greatest close to the ground (0-29 cm) in both high and low vegetation. The larval : nymphal ratio, at ground level at localities free of ground vegetation, varied between 8 : 1 and 32 : 1. In high vegetation, the greatest mean numbers of nymphal and adult ticks were at height intervals of 50-59 and 60-79 cm, respectively. These ranges are within the estimated height interval (40-100 cm) of the main part of the body surface of their preferred host, the roe deer (Capreolus capreolus). The presence of most questing I. ricinus larvae at ground level would favour the transmission of Borrelia burgdorferi s.l., since this is where the highly reservoir-competent rodents and shrews usually occur.     

Vertebrate hosts of Ixodes pacificus (Acari: Ixodidae) in California.

The western black-legged tick, Ixodes pacificus Cooley & Kohls, is an important parasite and vector of disease agents that affect human and animal health in the western United States. This paper presents a review of all published California host records for I. pacificus. Unpublished data from public health, academic, and vector control agencies and researchers were reviewed as well. Host species were identified for each active life stage (larvae, nymph and adult). A total of 108 vertebrate species in three classes (Mammalia, Aves, and Reptilia) were identified as hosts for at least one life stage of I. pacificus. Adult I. pacificus were recorded from 29 species of mammals, 2 species of birds, and 1 reptile species. Nymphal I. pacificus were recorded from 30 species of mammals, 38 species of birds, and 8 reptile species. Larval I. pacificus were recorded from 29 species of mammals, 43 species of birds, and 8 species of reptiles. A table depicting the taxonomic classification of host species is provided. This review adds eight new host records to the California list of recognized vertebrate host species for I. pacificus.     

The midgut hemolysin of Ixodes dammini (Acari:Ixodidae)

Midgut homogenates of the hard tick, Ixodes dammini, lyse erythrocytes from rabbits, rats, hamsters, and guinea pigs. The activity displays sigmoidal kinetics, has an alkaline pH optimum, and is activated by temperature. Hemolytic activity is lost when homogenates are incubated with trypsin or heated for 1 hr at 60 C. Activity is not detectable in nonfed ticks as well as ticks attached for up to 2 days to a host, but increases during the growth phase of feeding. Such activity is postulated to help the initial process of the blood meal digestion by releasing the contents of erythrocytes for further enzymatic hydrolysis.     

Reproductive strategies of the seabird tick Ixodes uriae (Acari: Ixodidae)

Ixodes uriae is a common ectoparasite of colonial seabirds in the circumpolar areas of both hemispheres. Despite its potential effects on host population dynamics and its role as a vector of pathogens, little is known about the reproductive strategies of this tick under natural conditions. Multiple mating of engorged females has been recorded in several instances, but the resulting paternity of offspring and its potential evolutionary significance have never been evaluated. Here, the paternity of offspring produced by females collected in the field was determined by using 5 polymorphic microsatellite markers. The results indicate that multiple mating in I. uriae can lead to multiple paternity in broods and, given the life history of this parasite, may be related to the adaptive benefits of producing genetically diverse offspring. Copulations took place both before and after the female's blood meal, but most successful fertilizations seemed to occur before engorgement. This suggests that the mating strategies of this tick may have evolved in response to local environmental constraints and, in particular, to the availability of conspecific ticks.     

Vector competence of Ixodes angustus (Acari: Ixodidae) for Borrelia burgdorferi sensu stricto

The vector competence of Ixodes angustus for Borrelia burgdorferi sensu stricto (s.s.) was investigated in the laboratory. The larval progeny of female ticks from Washington State were placed on Swiss-Webster mice that had been inoculated intravenously with 10⁸ spirochetes each of a Californian isolate of B. burgdorferi. Spirochetes were detected in 6 (12%) of 50 nymphs derived from larvae that had fed on these animals. Ten nymphs from the same cohort of experimentally infected ticks were placed on each of 4 naive deer mice (Peromyscus maniculatus). One of the mice seroconverted to B. burgdorferi and spirochetes were isolated from its ear tissues 4 weeks after exposure to ticks. Further vector competence trials were conducted with I. angustus ticks from California. Larvae were fed on deer mice that had been inoculated intradermally with B. burgdorferi along with larvae of I. spinipalpis as a comparison group. There was no significant difference in the prevalence of infection in nymphs of I. angustus (8.2%) versus those of I. spinipalpis (12.1%). We conclude that I. angustus is a competent experimental vector of B. burgdorferi s.s. and its efficiency for acquiring and transstadially passing such spirochetes is similar to that of I. spinipalpis.     

Population genetic structure of the tree-hole tick Ixodes arboricola (Acari: Ixodidae) at different spatial scales

The endophilic tick Ixodes arboricola infests cavity-nesting birds, and itsdispersal strongly depends on the movements of its host. Population genetic structureof I. arboricola was studied with seven polymorphic microsatellite markers.We collected 268 ticks from 76 nest boxes in four woodlots near Antwerp, Belgium.These nest boxes are mainly used by the principal hosts of I. arboricola,the great tit Parus major and the blue tit Cyanistes caeruleus. Asthese birds typically return to the same cavity for roosting or breeding, tickswithin nest boxes were expected to be highly related, and tick populations wereexpected to be spatially structured among woodlots and among nest boxes withinwoodlots. In line with the expectations, genetic population structure was found amongwoodlots and among nest boxes within woodlots. Surprisingly, there was considerablegenetic variation among ticks within nest boxes. This could be explained bycontinuous gene flow from ticks from nearby tree holes, yet this remains to betested. A pairwise relatedness analysis conducted for all pairs of ticks within nestboxes showed that relatedness among larvae was much higher than among later instars,which suggests that larvae are the most important instar for tick dispersal. Overall,tick populations at the studied spatial scale are not as differentiated as predicted,which may influence the scale at which host–parasite evolution occurs.     

Molecular identification of blood meal sources of ticks (Acari,Ixodidae) using cytochrome b gene as a genetic marker

Blood meal analysis (BMA) from ticks allows for the identification of natural hosts of ticks (Acari: Ixodidae). The aim of this study is to identify the blood meal sources of field collected on-host ticks using PCR analysis. DNA of four genera of ticks was isolated and their cytochrome b (Cyt b) gene was amplified to identify host blood meals. A phylogenetic tree was constructed based on data of Cyt b sequences using Neighbor Joining (NJ) and Maximum Parsimony (MP) analysis using MEGA 5.05 for the clustering of hosts of tick species. Twenty out of 27 samples showed maximum similarity (99%) with GenBank sequences through a Basic Local Alignment Search Tool (BLAST) while 7 samples only showed a similarity range of between 91–98%. The phylogenetic trees showed that the blood meal samples were derived from small rodents (Leopoldamyssabanus, Rattustiomanicus and Sundamysmuelleri), shrews (Tupaiaglis) and mammals (Tapirusindicus and Prionailurusbengalensis), supported by 82–88% bootstrap values. In this study, Cyt b gene as a molecular target produced reliable results and was very significant for the effective identification of ticks’ blood meal. The assay can be used as a tool for identifying unknown blood meals of field collected on-host ticks.     

Development of the salivary glands in embryos of Ixodes ricinus (Acari: Ixodidae)

We examined Ixodes ricinus embryos between 18 and 28 days of development with light, scanning and transmission electron microscopy. The differences in inner structure attested to establish three successive developmental stages: days 18-20, day 23, and days 26-28. Between 18 and 20 days the embryos are at early stages of organogenesis. Salivary glands cannot be identified at that stage. In 23-day-old embryos salivary glands are already outlined but the structure of alveoles is still different from that in larvae in which the embryonic development has been completed. Gland cells start to form alveoles and become active between 26 and 28 days of the development.     

The longevity of the tick Ixodes ricinus (Acari: Ixodidae) in Central Russia

The longevity of the tick Ixodes ricinus has been studied on 27 samples from a wild population of the Moscow Region. Ticks were kept in small cages and glass tubes under conditions close to natural. About 2/3 of the specimens collected in spring survived till the next spring and later died out gradually during the second season of their activity. Very few specimens reached the beginning of the third winter in their life, but apparently none of them survived the end of the winter. The life span of males was the same as that of females. No mass activation of adult ticks was recorded in the autumn of the year of their molting. It seems that the rise of the autumnal density of adult ticks depends mainly on the increased activity of the females which molted from nymphs last year.     

Development of the salivary glands in embryos of Ixodes ricinus (Acari: Ixodidae)

We examined Ixodes ricinus embryos between 18 and 28 days of development with light, scanning and transmission electron microscopy. The differences in inner structure attested to establish three successive developmental stages: days 18–20, day 23, and days 26–28. Between 18 and 20 days the embryos are at early stages of organogenesis. Salivary glands cannot be identified at that stage. In 23-day-old embryos salivary glands are already outlined but the structure of alveoles is still different from that in larvae in which the embryonic development has been completed. Gland cells start to form alveoles and become active between 26 and 28 days of the development. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential distribution of immature Ixodes dammini (Acari: Ixodidae) on rodent hosts

Ectoparasites such as ixodid ticks that remain attached to hosts for several days while feeding on blood are able to overcome the inflammatory and immune responses of some hosts and not others. The immature stages of the deer tick Ixodes dammini are found more frequently on the white-footed mouse, Peromyscus leucopus, than on other rodents. We propose that P. leucopus is more tolerant to I. dammini than is a less common host, the meadow vole, Microtus pennsylvanicus. To test this hypothesis, the distribution patterns and engorgement indices were determined for larval and nymphal I. dammini collected from wild-caught P. leucopus and M. pennsylvanicus. There were more immature ticks, which were more fully engorged, on P. leucopus than on M. pennsylvanicus. There were more and better engorged ticks on male than on female hosts. Laboratory studies on the number and weights of larval I. dammini collected off naive and previously exposed P. leucopus and M. pennsylvanicus support the results of the field study. Fewer larval ticks were recovered from previously exposed M. pennsylvanicus than P. leucopus, and the ticks weighed less. Larval and nymphal ticks aggregated among hosts in the study grid, and higher densities per male P. leucopus were correlated with higher engorgement indices, suggesting that immature I. dammini feed better at higher densities. The feeding success of I. dammini on its preferred host species might be due to its adaptation to the immune and inflammatory reactions of the host.     

Molecular identification key for pest species of Scirtothrips (Thysanoptera: Thripidae)

Effective plant quarantine and biological control initiatives require rapid and accurate identification of exotic and potentially invasive taxa that may cause high economic losses or environmental damage. The genus Scirtothrips Shull includes several species that are serious agricultural pests, and, because of their minute size and cryptic behavior, prone to undetected transport through international trade of plant material. Although assigning specimens to the genus Scirtothrips is straightforward using traditional taxonomic methods, identification of species is much more difficult and requires expert knowledge of the genus. Furthermore, the validity of some Scirtothrips species is questionable. Therefore, an easy, accurate, and highly reliable technique is desirable for Scirtothrips identification. Here, we provide a simple molecular key based on the internal transcribed spacer regions 1 and 2 (ITS1 and ITS2) of nuclear ribosomal DNA. Individual specimens can be identified by amplification of their ITS1 and ITS2 regions with general primers and determining the size of the products by using standard agarose gel electrophoresis, followed in some instances by DNA digestion with the restriction enzymes SacII or PspOM I. The advantage of this identification system is that nonspecialists are able to quickly and cheaply identify individual specimens. Material analyzed for this work was collected in the United States (California), India, South Africa, Kenya, Mexico, Guatemala, Honduras, Nicaragua, Costa Rica, Panama, Australia, New Zealand and Raiatea (Society Islands French Polynesia). We have identified seven pest species with the molecular-based methods described here. It is hoped that this system can be extended to other members of the genus as their ITS1 and ITS2 sequences become available. We also provide molecular confirmation for two new Scirtothrips species, one species from Honduras and one species from New Zealand.     

Seasonal and geographical distribution of adult Ixodes scapularis say (Acari: Ixodidae) in Louisiana.

The distribution and seasonality of adult black-legged ticks (Ixodes scapularis Say) in Louisiana was measured. The presence of adult ticks was determined by flagging at 106 sites throughout Louisiana. It was concluded that Ixodes scapularis is widely distributed throughout Louisiana. Ticks were also collected twice per month at one site over a 15-month period by flagging and use of CO2 traps to establish the relative seasonal abundance pattern of free-living adult ticks. Host-seeking, black-legged adult ticks were collected from October to May. Peak adult abundance was observed in December. More ticks were collected by the use of CO2 traps compared to flagging in October, November, and February. No black-legged tick larvae or nymphs were collected in this study using either collection method.     

Bodies of liquid water as a source of water gain for Ixodes ricinus ticks (Acari: Ixodidae)

It is well established that free-living unfed ticks can compensate for their inevitable body water losses by active water vapour absorption in periods of ambient relative humidity (RH) of greater than 75-90%. Whilst many species of terrestrial arthropods are known to be capable of locating liquid water and drinking when in need, the existing knowledge concerning the ecological significance of bulk water for rehydration in ticks is scarce. In the present laboratory study batches of unfed Ixodes ricinus (larvae, nymphs, and adults) in varying states of (de)hydration were supplied with tapwater either as droplets for 45 min in a Petri dish or in a small trough for 24 h. The body mass of each tick was gravimetrically determined before and after exposure. Though fully hydrated ticks were not usually attracted to liquid water, the response became increasingly positive with a growing body water deficit (p > 0.05). No tick was ever found with its mouthparts inserted into the water, nor had any tick residues of orange G in its alimentary tract when supplied with orange G-coloured water. Linear regression analysis demonstrated that water intake took place in a regulated manner in adult ticks, i.e. the more severely the ticks had been dehydrated the more net water they subsequently gained (p > 0.01). The maximum uptake rates were <20% of the original body mass per day. These findings indicate that unfed I. ricinus do not drink liquid water but are well able to use the high RH in the immediate vicinity of bulk water to actively take up vapour.     

Regeneration of Haller's sensory organ in the tick, Ixodes rubicundus (Acari: Ixodidae)

A study of regeneration in nymphs and adults of the South African tick Ixodes (Afrixodes) rubicundus, from which the forelegs had been amputated during the previous instar, revealed that the structural changes in regenerated Haller's sensory organs resemble those observed in other ixodid ticks, in particular in another prostriate tick, Ixodes (Ixodes) ricinus. The adult regenerates re-establish their atavistic features in terms of the increased number of different sensilla on the distal knoll, in the anterior pit and the capsule. The nymphal regenerates, in contrast, re-establish the features of the previous instar through a reduction in the number of some sensilla on the distal knoll and in the post-capsular area. The structural changes in different compartments of the organ appear independent. The phenomenon of regenerative induction through the appearance of specific changes in Haller's organ of the contralateral non-treated foreleg is probably characteristic only of prostriate ticks. A unique modification in the regenerated Haller's organ as revealed by duplication of the Haller's organ capsule was discovered in both I. rubicundus nymphs and adult ticks.     

Vertical migration of adult Ixodes rubicundus,the Karoo paralysis tick (Acari: Ixodidae)

Mortality due to Karoo paralysis amongst livestock is of considerable economic importance in South Africa. Indications are that the extent of vertical migration of adult ticks, to reach questing positions on grasses, is influenced by sudden climatic chages. Such influences as well as selection of questing substrates were investigated under controlled conditions. Vertical migration of adult Ixodes rubicundus on copper rods was determined in a square metal arena within a closed glass container in a room in which temperature and light could be controlled. Significantly more female and male ticks migrated vertically on 1.5 mm diameter rods than on 4.0 mm rods and on 450 mm long rods than on 100 mm rods. More ticks of both sexes migrated vertically at RH>80% than at RH<50% and at 12°C than at 21°C. More female than male and more older than younger ticks migrated vertically in all experiments. The results of this study contribute towards an understanding of the epidemiology of Karoo paralysis.