Role of cuticular lipids and water-soluble compounds in tick susceptibility to Metarhizium infection

The arthropod cuticle acts as a physiochemical barrier protecting the organism from pathogens' entry. Entomopathogenic fungi actively penetrate the cuticles of arthropod hosts and are therefore directly affected by cuticle composition. Previously we have observed that Metarhizium spp. developing on resistant ticks ultimately die without penetrating tick's cuticle, suggesting that the cuticles of resistant ticks have antifungal compounds. In the present study, lipids and water-soluble cuticular components were extracted from engorged female tick cuticles, of one susceptible and one resistant tick species to Metarhizium spp. While conidia exposed to lipids from the susceptible tick, Rhipicephalus annulatus, germinated and differentiated into appressorium, conidia exposed to lipids from the resistant tick, Hyalomma excavatum, were inhibited. Soluble cuticular component extracts from both susceptible and resistant ticks stimulated conidial germination but not appressorium differentiation. A comparative analysis of the fatty acid profile in lipid extract of each tick exhibited similar compositions, but the relative abundance of C16:0, C18:0, C18:1ω9C and C20:0 was 2–5 times higher in the extracts from resistant ticks. All of these fatty acids inhibited conidial germination in vitro at 1% and 0.1% w/v concentration, but C20:0 stimulated appressorium differentiation at low concentration. This is the first report demonstrating a possible link between the presence of antifungal compounds in a specific concentration in tick cuticle and tick resistance to infection.     

Resistant ticks inhibit Metarhizium infection prior to haemocoel invasion by reducing fungal viability on the cuticle surface

We studied disease progression of, and host responses to, four species in the Metarhizium anisopliae complex expressing green fluorescent protein (GFP). We compared development and determined their relative levels of virulence against two susceptible arthropods, the cattle tick Rhipicephalus annulatus and the lepidopteran Galleria mellonella, and two resistant ticks, Hyalomma excavatum and Rhipicephalus sanguineus. Metarhizium brunneum Ma7 caused the greatest mortality of R. annulatus, Metarhizium robertsii ARSEF 2575 and Metarhizium pingshaense PPRC51 exhibited intermediate levels of virulence, and Metarhizium majus PPRC27 caused low mortality of cattle ticks. Conidia of all four species germinated on all hosts examined, but on resistant hosts, sustained hyphal growth was inhibited and GFP emission steadily and significantly decreased over time, suggesting a loss of fungal viability. Cuticle penetration was observed only for the three most virulent species infecting susceptible hosts. Cuticles of resistant and susceptible engorged female ticks showed significant increases in red autofluorescence at sites immediately under fungal hyphae. This is the first report (i) of tick mortality occurring after cuticle penetration but prior to haemocoel colonization and (ii) that resistant ticks do not support development of Metarhizium germlings on the outer surface of the cuticle. Whether reduced Metarhizium viability on resistant tick cuticles is due to antibiosis or limited nutrient availability is unknown.     

Ticks (Acari: Ixodidae) infesting the Arabian Camel (Camelus dromedarius) in the Sinai,Egypt with a note on the acaricidal efficacy of Ivermectin

In this study, tick burdens on camels (Camelus dromedarius) were determined in the vicinity of the St. Catherine monastery, Sinai, Egypt. In total 2,545 ticks (1,491 adults and 1,054 nymphs) were collected and identified. Mean tick burdens were relatively heavy and the range in number of ticks per camel was very broad (6–173). Hyalomma dromedarii was the predominant tick species and accounted for 95.6% of the adult ticks. Other ticks found were H. marginatum subspp. and H. anatolicum excavatum. All nymphs collected were Hyalomma spp.In addition, the effect of ivermectin (Ivomec MSD AGVET) on tick burdens, when given subcutaneously at 0.2 mg/kg¹, was evaluated in nine camels in the date-palm plantation of Kibbutz Yahel in the Arava valley, Israel. Initial tick burdens on these camels (half-body tick counts) ranged from 20–105 ticks per camel. Seven camels from the same herd with half-body tick counts ranging from 40–107 ticks per camel were not treated and served as a control group. Ivermectin was not effective against Hyalomma tick infestation in camels under these conditions.     

Tick pathogenicity,thermal tolerance and virus infection in Tolypocladium cylindrosporum

Tolypocladium cylindrosporum is a fungus which has been isolated from soil, from asymptomatic plants as an endophyte and has been shown to be pathogenic to several species of arthropods. The objective of the present work was to study a collection of T. cylindrosporum strains to evaluate the characteristics of this fungus as a bioacaricide. The pathogenicity of five different strains of T. cylindrosporum was tested against two tick species, Ornithodoros erraticus and Ornithodoros moubata. Both tick species were susceptible to all the fungal strains. Mortality was greater for O. erraticus and differed among the five developmental stages of the ticks tested and among the fungal treatments. Mean mortality rates were close to 60% for O. erraticus, similar to those reported for other entomopathogenic fungi used for this purpose. The responses of 11 different strains of the fungus to 22°C and 30°C were also studied. Significant differences in temperature tolerance occurred among the strains and growth inhibition was observed at 30°C. Several mycoviruses were found infecting 5 of the 11 strains. However, no clear relationship was found between the presence of viruses and fungal growth or pathogenicity.     

The seasonal occurrence of ticks (Acari: Ixodidae) on sheep and in the field in the Judean area of Israel

A 2 year survey of ixodid ticks in the Judean area of Israel between 1983 and 1985 showed that sheep were parasitized by the following species:Rhipicephalus sanguineus group (30.6%),Rhipicephalus bursa (25.3%),Haemaphysalis cretica (20.5%),Haemaphysalis otophila (20.1%) andHyalomma anatolicum excavatum (3.1%). Three other species,Hyalomma marginatum rufipes, Boophilus annulatus andAmblyomma lepidum were also present but in very low numbers. A total of 50 816 specimens (78.1% adult ticks) were collected from the sheep. In the field, a total of 4780 ticks (8.7% adults) were collected and 64.3% consisted ofR. bursa. Other species found wereH. cretica (14.5%),H. a. excavatum (13.7%),H. otophila (3.4%),R. sanguineus group (1.9%) and 1.7% wasIxodes eldaricus. The number of ticks collected varied from year to year and seasonal activity was observed in all species except forH. a. excavatum. In all species, males outnumbered females, with the exception ofH. cretica. The seasonal occurrence, tick ecology and disease relationship is discussed for each species.     

Experimental infection of the rabbit tick,<Emphasis Type="Italic"> Haemaphysalis leporispalustris</Emphasis>, with the bacterium<Emphasis Type="Italic"> Rickettsia rickettsii</Emphasis>, and comparative biology of infected and uninfected tick lineages

The present study consisted of two experiments that evaluated experimental infections of Haemaphysalis leporispalustris ticks by a Brazilian strain of Rickettsia rickettsii, and their effect on tick biology. In experiment I, ticks were exposed to R. rickettsii during the larval, nymphal or adult stages by feeding on rabbits (Oryctolagus cuniculus) needle-inoculated with R. rickettsii, and thereafter reared on uninfected rabbits for the entire next tick generation. Regardless of the tick stage that acquired the infection, all subsequent tick stages were shown to be infected by PCR (infection rates varying from 1.3 to 41.7%), and were able to transmit R. rickettsii to uninfected rabbits, as demonstrated by rabbit seroconversion, guinea pig inoculation with rabbit blood, and PCR on rabbit blood. In Experiment II, ticks were exposed to R. rickettsii during the larval stage by feeding on rabbits co-infested with R. rickettsii-infected adult ticks, and thereafter reared on uninfected rabbits until the next generation of larvae. Again, all subsequent tick stages were shown to be infected by PCR (infection rates varying from 3.0 to 40.0%), and were able to transmit R. rickettsii to uninfected rabbits. Thus, it was demonstrated that larvae, nymphs, and adults of H. leporispalustris were able to acquire and maintain the R. rickettsii infection by transstadial and transovarial transmissions within the tick population, with active transmission of the bacterium to susceptible rabbits by all parasitic stages. Analyses of biological parameters of uninfected and R. rickettsii-infected tick lineages were performed in order to evaluate possible deleterious effects of R. rickettsii to the infected tick lineages. Surprisingly, all but one of the four R. rickettsii-experimental groups of the present study showed overall better biological performance than their sibling uninfected control ticks. Results of the present study showed that H. leporispalustris could support infection by a high virulent strain of R. rickettsii for at least two generations, in which infected tick lineages tended to have better performance than uninfected ticks. Our results support a possible role of H. leporispalustris in the enzootic maintenance of R. rickettsii in Latin America, as previously suggested by earlier works.     

Metarhizium anisopliae conidial responses to lipids from tick cuticle and tick mammalian host surface

Conidial germination and the formation of appressoria are important events in the interactions between entomopathogenic fungi and their arthropod hosts. In this study, we demonstrate the effects of lipids extracted from tick epicuticle and the surface of a mammalian host (calf) on conidial germination and the development of appressoria in two subspecies of Metarhizium anisopliae, M. anisopliae var. anisopliae (M.an.an.-7) and M. anisopliae var. acridum (M.an.ac.-5), which have different levels of virulence toward ticks. Pentane extracts of epicuticles of ticks susceptible and resistant to fungal infection always stimulated the germination of M.an.an.-7 conidia and the development of their appressoria; whereas the effects of dichloromethane (DCM) extracts of tick epicuticle varied depending on the tick. The DCM extracts from most of the tick species and developmental stages stimulated conidial germination and/or the formation of appressoria in M.an.an.-7. However, a DCM extract of lipids from the most resistant tick, engorged Hyalomma excavatum female, inhibited the germination of M.an.an.-7 conidia. Conidia of the non-virulent M.an.ac.-5 did not germinate on agarose amended with any of the examined tick extracts. However, when the tick extracts were placed on bactoagar, conidial germination increased 7- to 8-fold. Extracts from the skin, hair and ear secretions of a calf stimulated conidial germination and the formation of appressoria in M.an.an.-7, but not M.an.ac.-5. This study demonstrates that lipids from tick epicuticles and mammalian skin selectively affect the germination of conidia of entomopathogenic fungi. The effects of these lipids may explain the variability in tick control these fungi provide for different hosts.     

Effects of combining the fungi <Emphasis Type="Italic">Beauveria bassiana</Emphasis> and <Emphasis Type="Italic">Metarhiziumanisopliae</Emphasis> on the mortality of the tick <Emphasis Type="Italic">Amblyomma variegatum</Emphasis> (ixodidae) in relation to seasonal changes

The effect of formulation, fungal concentration, type and seasonal changes on the mortality of the tick Amblyomma variegatum was investigated. A previous study demonstrated high pathogenicity of strains of the fungi Beauveria bassiana and Metarhizium anisopliae against the ticks Rhipicephalus appendiculatus and Amblyomma variegatum (Kaaya et al. J Invertebr Pathol 1996; 67: 15–20). The present study was undertaken to explore possible additive or synergistic effects of the two fungi on A. variegatum. The effects of oil and water formulations at different concentrations of each fungus and combination of the two on the mortality of A. variegatum in the laboratory and in the field during the wet and dry seasons were determined and compared. The oil formulation performed better in all assays, with highest tick mortality of 92% occurring during the wet season at conidia concentration of 1 × 10¹⁰ conidia/ml of the mixed fungi compared to 49% for the water formulation at similar conidia concentration. However, at the same conidial concentration during the dry season, mortalities in the field were relatively low with the mixture of the fungi recording 24% and 17% tick mortality for the oil and water formulation respectively. The effect of infecting the ticks with a cocktail of the two fungi was inconclusive under more controlled conditions in the laboratory but field results under both wet and dry seasons indicated significant differences between the separate and mixed fungi infections. The results demonstrate a potential of cocktail formulations in the control of ticks and possibly of other arthropod pests.     

Preliminary studies on the effect of Anaplasma marginale antibodies ingested by Dermacentor andersoni ticks (Acari:Ixodidae) with their blood meal on infections in salivary glands

The effect of Anaplasma marginale antibodies ingested with the tick blood meal was tested on infected male ticks that were allowed to feed on cattle immunized with the erythrocytic stage of A. marginale. The experiments were done in two trials. Trial 1 was done using splenectomized calves (two calves per treated and control groups) while ticks in trial 2 were fed on intact yearling cattle (four cattle per treated and control groups). The cattle were immunized with purified outer membrane proteins of erythrocyte-derived A. marginale using saponin (trial 1) or monophosphoryl lipid-A-trehalose dicorynomycolate adjuvant (trial 2). The corresponding control cattle received adjuvant only. All cattle were challenged using Dermacentor andersoni males infected as adults that were allowed to feed for 7 days. In trial 1, the ticks were allowed to feed a second time on susceptible calves to test whether exposure of ticks to immunized cattle affected their ability to transmit anaplasmosis. Infections in fed ticks were monitored by determining the infection rates in salivary glands with an A. marginale-specific RNA probe and light microscopy. Vaccine-derived antibodies ingested with the tick blood meal did not appear to affect the development of A. marginale in previously infected ticks. The infection rates in the salivary glands were not significantly different among ticks fed on immunized versus adjuvant control cattle. When the vaccine-exposed ticks in trial 1 were allowed to feed a second time on susceptible calves, the resulting clinical symptoms of anaplasmosis were similar to those of the controls. There was no statistically significant effect of tick exposure to the anti-erythrocytic stage antibody on the development of salivary gland infection or transmission of A. marginale by ticks.     

Pathogenicity of 17 isolates of entomophagous nematodes (Steinernematidae and Heterorhabditidae) for the ticks Amblyomma variegatum (Fabricius), Boophilus microplus (Canestrini) and Boophilus annulatus (Say)

Entomopathogenous nematodes are well known biocontrol agents of insects. They live in the superficial layer of the soil, a location where ticks accomplish their molt and where they oviposit their eggs, making them, theoretically, the preys of infective larvae of nematodes. Seventeen strains of entomopathogenous nematodes: eight strains of Steinernema and nine strains of Heterorhabditis were placed in contact with each of the free living stages of three tick species: Amblyomma variegatum, Boophilus microplus and B. annulatus. The first two species were resistant to all the nematode strains that were tested, whereas B. annulatus was susceptible to all of them. Ovipositing females were more susceptible than females during the preoviposition period. There were no anatomical differences between the two species of Boophilus which can account for such differences in their susceptibility. The use of nematodes to control some species of ticks should be considered.     

Performance of a Prototype Baited-trap in Attracting and Infecting the Tick Amblyomma variegatum (Acari: Ixodidae) in Field Experiments

Investigations were commenced to study the potential use of the fungi, Beauveria bassiana, Metarhizium anisopliae, and the attraction-aggregation-attachment pheromone (AAAP) for the control of Ambloyomma variegatum as an environmentally friendly technology. The objective of the study was to develop and test a device, which could be used for pheromone and carbon dioxide delivery and infection of ticks with the fungi in an attempt to control the tick populations in the vegetation. Using a pheromone-baited device treated with the fungi mixture, 79% of the ticks released were attracted and exposed to the fungi and of these, 78% died during incubation in the laboratory. In another set of experiments, of the released ticks that were similarly exposed to fungi using the pheromone-baited device and left in the vegetation, 33.8% were recovered compared to recoveries of between 76 and 84% in the controls. These results were significantly different at the 5% level, an indication that the pheromone/fungi mixtures had significant effect in reducing the tick population in the field.     

Hyalomma ticks on northward migrating birds in southern Spain: Implications for the risk of entry of Crimean‐Congo haemorrhagic fever virus to Great Britain

Crimean‐Congo haemorrhagic fever virus (CCHFV) is a zoonotic virus transmitted by Hyalomma ticks, the immature stages of which may be carried by migratory birds. In this study, a total of 12 Hyalomma ticks were recovered from five of 228 migratory birds trapped in Spring, 2012 in southern Spain along the East Atlantic flyway. All collected ticks tested negative for CCHFV. While most birds had zero Hyalomma ticks, two individuals had four and five ticks each and the statistical distribution of Hyalomma tick counts per bird is over‐dispersed compared to the Poisson distribution, demonstrating the need for intensive sampling studies to avoid underestimating the total number of ticks. Rates of tick exchange on migratory birds during their northwards migration will affect the probability that a Hyalomma tick entering Great Britain is positive for CCHFV. Drawing on published data, evidence is presented that the latitude of a European country affects the probability of entry of Hyalomma ticks on wild birds. Further data on Hyalomma infestation rates and tick exchange rates are required along the East Atlantic flyway to further our understanding of the origin of Hyalomma ticks (i.e., Africa or southern Europe) and hence the probability of entry of CCHFV into GB.     

Comparative response of Metarhizium brunneum to the cuticles of susceptible and resistant hosts

Earlier studies demonstrated that Metarhizium brunneum, usually a broad-host pathogen of arthropods, is unable to complete its pathogenic life cycle when inoculated on the fungus-resistant tick, Hyalomma excavatum engorged females. While the fungus penetrates the cuticle of fungus-susceptible tick, Rhipicephalus annulatus females, it is unable to penetrate the cuticle of fungus-resistant tick, and even perishes on its surface. This is probably due to high concentration of antifungal fatty acids and probably also due to a hypersensitive-like response of the tick. To understand the metabolic pathways occurring in the fungal hyphae upon encountering the cuticles, we compared the response of the fungus to cuticle from susceptible and resistant tick cuticles by 2D-gels. The intracellular proteomes of M. brunneum Mb7 exposed to cuticle of the fungus-susceptible tick, R. annulatus, and to the fungus-resistant tick, H. excavatum engorged females were compared after exposure to either cuticles. By means of liquid chromatography-mass spectrometry/mass spectrometry we identified in both proteomes common proteins involved in biological processes as well as unique proteins identified only in the proteome of fungus exposed to fungus-resistant tick cuticle. These proteins were identified in high probability as heat shock proteins, four key enzymes of the glyoxylate cycle, and proteins associated with hypoxia, and exposure to antifungal drugs. These findings are discussed within the M. brunneum-tick pathosystem in relation to tick resistance and host resistance in general.     

Distribution and seasonal activity of tick species on cattle in the West Aegean region of Turkey

The aim of the present study was to determine the identity, seasonal activity and distribution of tick species of cattle in the West Aegean region of Turkey between June 2006 and May 2008. Nine villages within three provinces, viz. Manisa, Izmir and Aydin, were included in the study and a total of 75 animal barns were visited monthly for a period of 24 months and 443 cattle were examined for the presence of ticks. It was determined that 23% of cattle were infested with ticks. A total of 19,679 adult ticks were collected. The most abundant tick species was Hyalomma marginatum (33.5%) and H. excavatum (16.9%) in the study area. Seasonal appearance of the adult ticks varied among species. Adult ticks of the Hyalomma genus were present throughout the year, although in smaller numbers during the winter. Species of Rhipicephalus were detected in all seasons except autumn. Rhipicephalus (Boophilus) annulatus was identified in July and August, Haemaphysalis parva was detected during the autumn. Ixodes ricinus and Dermacentor marginatus were identified during spring, autumn and winter. The study demonstrated the presence of I. ricinus, D. marginatus, Hyalomma rufipes and Hae. parva for the first time in the West Aegean region of Turkey.     

Attachment site selection of ticks on roe deer, <Emphasis Type="Italic">Capreolus capreolus</Emphasis>

The spatio-temporal attachment site patterns of ticks feeding on their hosts can be of significance if co-feeding transmission (i.e. from tick to tick without a systemic infection of the host) of pathogens affects the persistence of a given disease. Using tick infestation data on roe deer, we analysed preferred attachment sites and niche width of Ixodes ticks (larvae, nymphs, males, females) and investigated the degree of inter- and intrastadial aggregation. The different development stages showed rather consistent attachment site patterns and relative narrow feeding site niches. Larvae were mostly found on the head and on the front legs of roe deer, nymphs reached highest densities on the head and highest adult densities were found on the neck of roe deer. The tick stages feeding (larvae, nymphs, females) on roe deer showed high degrees of intrastadial spatial aggregation, whereas males did not. Male ticks showed large feeding site overlap with female ticks. Feeding site overlap between larval-female and larval-nymphal ticks did occur especially during the months May–August on the head and front legs of roe deer and might allow pathogen transmission via co-feeding. Tick density, niche width and niche overlap on roe deer are mainly affected by seasonality, reflecting seasonal activity and abundance patterns of ticks. Since different tick development stages occur spatially and temporally clustered on roe deer, transmission experiments of tick-borne pathogens are urgently needed.     

Laboratory studies of ant predation on parapatric reptile ticks

Abstract Two reptile tick species, Aponomma hydrosauri and Amblyomma limbatum, have a parapatric distribution in South Australia. Predation may play a role in maintaining the boundary. Laboratory colonies of Rhytidoponera and Iridomyrmex ants were collected from near Mt Mary, South Australia, close to the tick boundary. They were tested as predators of the two tick species. In the experiments, ticks in leaf litter were more protected from predation than those on bare soil. When comparing leaf litter types from the Mt Mary area, mallee litter was more protective than bluebush litter of equivalent depth. Ticks positioned at the base of the litter layer were more protected from predation than those at the litter surface, and Amb. limbatum ticks were more resistant to predation than Ap. hydrosauri ticks. These results contribute to our understanding of the mechanisms maintaining the abrupt parapatric boundary between the two tick species. Predators may contribute to preventing the more susceptible Ap. hydrosauri from spreading further north, where bluebush litter is more common, and so predation risk is higher. Predators probably have less influence in preventing Amb. limbatum from spreading further south.     

Genetic variants in interferon gamma (<Emphasis Type="Italic">IFN-γ</Emphasis>) gene are associated with resistance against ticks in <Emphasis Type="Italic">Bos taurus</Emphasis> and <Emphasis Type="Italic">Bos indicus</Emphasis>

In tropical and subtropical regions of the world, parasitic diseases are major obstacle in the health and ultimately overall performance of animals. Cattle express heritable, contrasting phenotypes when exposed to ticks depicting genetic nature of trait. IFN-γ is one of the most reported genes critical for innate and adaptive immunity against viral and intracellular infections. To identify its role in resistance for ectoparasite especially tick, genetic characterization of this gene was done in resistant and susceptible animals of Sahiwal cattle (n = 95) and Friesian (n = 92). Nine Polymorphisms were identified, three of them were found in exonic region. One out of nine variants was being reported previously (ss82716193) and was confirmed in Pakistani Sahiwal cattle population as well. Single site analysis of each variant depicted their significance in tick resistant and tick susceptible groups (P < 0.05). The associations using haplotypes were more informative than for single markers. Eighteen different haplotypes resulting from nine polymorphic sites were used in construction of maximum parsimony tree which categorized resistant and susceptible animals in two clades. Genetic markers identified in this study can be useful in future breeding selection programs against tick resistance.     

Spotted Fever Group <Emphasis Type="Italic">Rickettsiae</Emphasis> in Ticks in Cyprus

In two surveys conducted from March 1999 to March 2001 and from January 2004 to December 2006, a total of 3,950 ticks (belonging to ten different species) were collected from seven domestic and wild animals (goat, sheep, cattle, dog, fox, hare, and mouflon) from different localities throughout Cyprus. In order to establish their infection rate with Spotted Fever Rickettsiae (SFG), ticks were pooled and tested by polymerase chain reaction targeting gltA and ompA genes, followed by sequencing analysis. When tick pools tested positive, individual ticks were then tested one by one, and of the 3,950 ticks screened, rickettsial DNA was identified in 315 ticks (infection rate, 8%). Five SFG Rickettsiae were identified: Rickettsia aeschlimannii in Hyalomma marginatum marginatum, Rickettsia massiliae in Rhipicephalus turanicus and Rhipicephalus sanguineus, Rickettsia sibirica mongolotimonae in Hyalomma anatolicum excavatum, and a Rickettsia endosymbiont of Haemaphysalis sulcata (later described as Rickettsia hoogstraalii) in Haemaphysalis punctata. Two additional genes, 17 kDa and ompB, were targeted to characterize a new genotype of “Candidatus Rickettsia barbariae” genotype in R. turanicus, designated here as “Candidatus Rickettsia barbariae” Cretocypriensis. These results confirm the presence of a spectrum of SFG Rickettsiae on the island. Further studies are necessary to gain better knowledge on the epidemiology of SFG Rickettsiae in Cyprus.     

Compatibility of Metarhizium anisopliae with Calpurnia aurea leaf extracts and virulence against Rhipicephalus pulchellus

Leaf extracts of Capurnia aurea (Fabaceae) have been reported to attract ticks and can be considered for use in combination with entomopathogenic fungus in an autodissemination approach, whereby ticks that are attracted to baited traps are infected with the inoculum. Bioassays were undertaken to assess the compatibility of aqueous, methanol and acetone extracts of C. aurea with conidia of Metarhizium anisopliae sensu stricto (ss) (Hypocreales: Clavicipitaceae) isolate ICIPE 7 in terms of mycelial growth, conidial production and spore viability. Aqueous extract of C. aurea was compatible with the fungus at all the concentrations tested whereas methanol and acetone extracts inhibited all the fungal growth parameters. The virulence of M. anisopliae formulated in different extracts of C. aurea was also tested against different developmental stages of Rhipicephalus pulchellus in laboratory bioassays. No significant differences in virulence were observed between M. anisopliae applied alone and M. anisopliae formulated in different concentrations of extracts of C. aurea among the larvae, nymphs and adults. However, mortality varied according to the developmental stage, with larval stage being the most susceptible. Aqueous extract was compatible with M. anisopliae and could be therefore mixed together for ‘spot‐spray’ treatments as low cost and environmentally friendly technology for tick control in grazing pasture.     

Repellencies and toxicities of five ant-derived defensive compounds against the lone star tick, <Emphasis Type="Italic">Amblyomma americanum</Emphasis> (Acari: Ixodidae)

The lone star tick, Amblyomma americanum, is a vector of several important human and animal diseases. This tick species has rapidly expanded in its geographic distribution, and its aggressive behavior has increased the risk of tick-borne diseases in these new areas. Repellents are recommended by the Centers for Disease Control and Prevention (CDC) for protection against tick bites. DEET is the most common repellent, but public concerns over its safety have increased the need for alternative safe and efficacious tick repellents. Several naturally derived animal compounds have been tested against other species of ticks or other arthropod pests, but not against A. americanum. Based on EC₅₀ values obtained using a vertical paper bioassay, decylamine and MT-710 (a 2-tridecanone formulation) were found to be as repellent as DEET. Those two substances along with 2-tridecanone were also found to be as repellent as DEET when their EC₉₅ values were compared. Lone star ticks were more susceptible to the toxic effects of DEET in glass vial assays than all of the ant-derived defensive compounds/formulations. These results suggest that the ant-derived defensive compounds are likely more effective lone star tick repellents than DEET, but they are not as toxic as DEET towards the ticks. The suitability of these compounds for use as personal repellents, as well as at the landscape scale, should be explored.