The Ivomec SR Bolus for control of Boophilus annulatus (Acari: Ixodidae) on cattle in South Texas.

When Hereford heifers infested with Boophilus annulatus (Say) were treated with a single Ivomec SR Bolus, the concentration of ivermectin in the serum of the treated cattle reached a maximum of 8.8 +/- 0.9 ppb at 2 wk posttreatment. The single bolus treatment resulted in 84.4% control of standard engorging B. annulatus females on treated cattle over the 20-wk trial. Although fewer engorged ticks were collected from the sentinel heifers exposed in the treated pasture than those in the control pasture at weeks 4, 10, and 16 posttreatment, none of the differences was statistically significant. Each exposure of sentinel cattle found free-living ticks in both the treated and control pastures, indicating the infestation was not eliminated by the treatment. When the trial was repeated using two Ivomec SR Boluses/heifer, the concentration of ivermectin in the serum of the treated cattle reached a maximum level of 31.2 +/- 3.9 ppb at week 13 posttreatment. The use of two boluses/heifer resulted in 99.6% control of standard engorging B. annulatus females over the 20-wk trial. No ticks were found on sentinels placed in the treated pasture after week 9 posttreatment, an indication that the treatment had eliminated the free-living population in the treated pasture. From these studies, we conclude that a single Ivomec SR Bolus is incapable of sufficient control of B. annulatus to meet the rigid requirements of the Cattle Fever Tick Eradication Program in South Texas. Although two boluses per animal did eliminate the ticks from treated heifers and the pasture they were in, the treatment would not be sufficiently efficacious for mature cattle (>400 kg) for it to be useful in the program.     

Evaluation of a Pour-on Formulation of Fipronil Against Boophilus Annulatus (Acari: Ixodidae) Under Natural South Texas Field Conditions

A long-term field study (60 consecutive weeks) was conducted to determine whether a Boophilus annulatus (Say) population could be eradicated through repeated applications of a 1% pour-on formulation of fipronil on cattle held in an infested pasture. Animals treated repeatedly over time (seven applications) were infested with significantly fewer (p < 0.05) female ticks (5 mm in size) than untreated animals in all except one of the 57 weekly tick counts conducted after the first treatment was applied. As the number of treatments increased over time, there was a progressive decrease in the number of instances in which engorging females were observed on the treated cattle. Tick numbers obtained from sentinel cattle placed in pasture with untreated and treated cattle at various intervals throughout the study indicated that a single fipronil treatment had no observable adverse effect on the field tick population. However, after two treatments had been applied, there were always dramatically fewer ticks obtained from sentinel animals placed with treated cattle than were observed on sentinel animals placed with untreated cattle. Furthermore, tick numbers obtained from sentinel cattle placed with treated cattle over time indicated that the tick population in the pasture declined by stages. While a single treatment had no effect on the tick population, the application of two to four fipronil treatments at various intervals dramatically reduced the tick population, even though substantial numbers of females were still present on the sentinel animals. Ultimately, the application of five to seven fipronil treatments resulted in an extremely low tick population in the pasture, although total eradication of the population was not achieved during the study. The mean weight gain of treated animals was significantly higher (p < 0.05) than untreated animals during the study, indicating that the fipronil treatments had a highly beneficial impact on weight gain production.     

Failure of white-tailed deer, Odocoileus virginianus L., to sustain a population of cattle ticks, Boophilus annulatus (Say), through successive generations

Cattle ticks, Boophilus annulatus (Say), previously reared only on cattle, were placed on 3 white-tailed deer, Odocoileus virginianus L. Ticks were maintained through successive generations solely on the same deer as they aged (3, 6, and 9 mo of age) and received repeated challenges (0, 1, and 2 previous challenges). Cattle were infested simultaneously to assess tick viability and provide a comparison of tick numbers, female weight, egg mass weight, and egg hatch. The initial infestation (3,000 larvae/animal) produced a mean of 12.7 and 506.7 females from deer and cattle, respectively. Ticks recovered from deer weighed less, laid smaller egg masses, and had lower egg hatchability than cattle-reared ticks. A second infestation (3,000 larvae/animal) produced a 6.3-fold reduction in tick numbers on deer (means = 2.0 females/deer), whereas the number on cattle increased (means = 578.0 females/calf). Ticks reared on the deer were again smaller, laid fewer eggs, and had lower egg hatch, although differences were not significant. A third infestation of deer (1,900 larvae/deer) produced only 1 engorged female tick and no viable eggs, thus eliminating the population of deer-reared ticks within 3 generations. Results of the study suggest that a population of B. annulatus will not be sustained indefinitely through time solely on deer; thus, efforts to reduce deer populations severely as a means of eradicating ticks are unnecessary.     

Partial strategic tick control within a herd of European breed cattle in the state of Rio Grande do Sul,southern Brazil

A trial is described, in the state of Rio Grande do Sul, southern Brazil, as one of a series suggested to investigate the effects of strategic but selective acaricide treatments of cattle within herds against Boophilus microplus. They are aimed at considering the repercussions of farmer attempts at immediate reductions in acaricide costs and the potential for creation of ‘refugia’ of untreated ticks. Half (Group 1) of a small experimental herd of European breed heifers were treated strategically against ticks, three times during the late spring–early summer and twice during autumn (southern hemisphere), with an injectable avermectin endectocide, designed to act directly against the first and third generations of parasitic B. microplus per ‘cattle tick year’ at this site, respectively. The consequent levels of infestations on all of the member cattle in their common pasture were monitored. Group 1 showed low to zero tick counts during the 28-day treatment interval periods and up to ca. 14 days after the last of such a series. Treated cattle, however, became re-infested outside of these periods and to levels that would be considered as unacceptable by farmers in the state. The untreated cattle (Group 2) showed infestations at generally higher levels, than their contemporaries, within and outside of the treatment periods. There were thus ample sources of larvae in the pasture, derived principally from falling, untreated engorged female ticks, re-infesting both the treated and untreated cattle. Advantages of maintaining chemically untreated cattle ticks within a herd, compared to their disadvantages as contaminants to classical strategic control procedures, merit re-evaluation, especially in relation to the recent, world-wide resurgence of acaricide resistance in B. microplus. This revised version was published online in July 2006 with corrections to the Cover Date.     

Factors affecting the virulence of entomopathogenic nematodes to engorged female Boophilus annulatus ticks

The laboratory trials rank the virulence of entomopathogenic nematode strains (3 heterorhabditids and 6 steinernematids) to engorged female Boophilus annulatus ticks according to 3 parameters of the infection process: the effect of exposure time on tick mortality, the quantity of nematodes that penetrate ticks, and the rate of tick mortality after the injection of 1, 2, or 3 nematodes. Exposure of the ticks to heterorhabditid strains for 6 hr resulted in >80% mortality, but only 20 or 65% mortality after exposure to most steinernematids. The quantity of nematodes recovered per tick exposed to nematodes for 6 days averaged from 16 to 141. For steinernematids, a negative correlation was obtained between tick mortality and the average quantity of nematodes recovered. Injecting 1 infective juvenile from 1 of 2 heterorhabditid strains into each tick resulted in close to 100% mortality. Increasing the quantity of nematodes injected into each tick had little or no additive effect on tick mortality.     

Prevalence of ixodid ticks on cattle in Mazandaran province, Iran

A survey was carried out to investigate the prevalence of hard tick species (Acari: Ixodidae) on cattle in Mazandaran province, Iran. A total of 953 ticks were collected from 86 infested cattle during activating seasons of ticks during 2004-2005. Nine species were identified: Boophilus annulatus (51.3%), Rhipicephalus bursa (16.8%), Haemaphysalis punctata (6.3%), Ixodes ricinus (6.8%), Hyalomma marginatum (12.5%), Hyalomma anatolicum excavatum (5.2%), Hyalomma asiaticum (0.6%), Hyalomma detritum (0.2 %), and Dermacentor spp. (0.1%). The results show that Boophilus annulatus, Rhipicephalus bursa, and Hyalomma species are dominant tick species in the surveyed area.     

Role of Rusa deer Cervus timorensis russa in the cycle of the cattle tick Boophilus microplus in New Caledonia

Two field experiments were conducted to evaluate the efficiency of Rusa deer in the development of the cattle tick Boophilus microplus in comparison with that of steers in the same pastures and under the same conditions of infestation. No difference was noted between a mixed steer/deer herd and a pure steer or pure deer herd in the infestation pattern of each host, suggesting that attachment to the alternative host is mechanical and not affected by the simultaneous presence of the primary host on the pasture. Deer are capable of producing engorged viable females, with weight and reproductive performances similar to or even better than females fed on steers. For moderate levels (1 million larvae per hectare) and high levels (32 million larvae per hectare) of pasture infestation, tick burdens on steers were not very different (e.g. average 1911 and 2681ticks per m² skin, respectively, on day 24). This may be because of saturation of steer skin sites at the moderate larval dose. Deer harboured 2.7–33 times fewer ticks than steers and produce no engorged females at the moderate larval level and 32 times fewer engorged females than steers at the high larval level. Infestation of deer was dosedependent with averages of 12 and 399ticks per m² skin on day 25 at the moderate and high larval levels, respectively. At a high infestation level of the environment, Rusa deer may contribute, but to a limited extent, to infestation of pastures and, consequently, of cattle. However, their role in sustaining a viable tick population requires further investigation.     

Monthly dynamics of ticks (Acari: Ixodida) infesting N'Dama cattle in the Republic of Guinea

The occurrence of ixodid ticks on N'Dama cattle was studied in the Republic of Guinea between June 1994 and May 1995. Monthly tick collections were performed on 80 animals from 14 villages located in Dabola, Kouroussa and Dinguiraye prefectures. A total of 19,804 ticks was collected and classified using standard taxonomic keys. The following tick species were identified: Amblyomma variegatum, Hyalomma marginatum rufipes, Hyalomma trunctum, Hyalomma nitidum, Rhipicephalus lunulatus, Rhipicephalus muhsamae, Rhipicephalus senegalensis, Rhipicephalus sulcatus, Rhipicephalus turanicus, Boophilus annulatus, Boophilus geigyi. Boophilus spp. were the most numerous adult ticks (57.1%), Am. variegatum adults constituted 27.4%, while 12.4% were Rhipicephalus spp. and 2.5% Hyalomma spp. Rhipicephalus turanicus and Hyalomma nitidum were recorded for the first time in the country. Am. variegatum and Boophilus spp. were present throughout the year, whereas Am. variegatum adults showed a peak during the rainy season between April and September. Immature stages collected belonged exclusively to the genera Amblyomma and Boophilus. Am. variegatum larvae and nymphs showed a peak during the dry season (October-March); no significant variation between seasons was observed for Boophilus immatures. A significantly higher infestation of cattle by Rhipicephalus spp. was found in Dabola and Kouroussa prefectures, located in the southern part of the study area, with similar climatic, vegetation and rainfall characteristics. Possible options for the control of ticks in the study area are briefly discussed.     

An experimental investigation into the effects of flooding on the ixodid tick Boophilus microplus (Canestrini)

Summary The effect of water immersion on the non-parasitic stages of Boophilus microplus were investigated both under laboratory and field conditions. Survival of engorged female ticks was influenced by their age and the temperature of the water. Eggs and larvae were more resistant to submerison than were engorged females and their survival was increased at low temperatures and in water with high oxygen content. The persistence of this tick in areas prone to flooding was attributed to the survival of parasitic stages and to larvae on the pasture. Heavy rains produce favourable pasture conditions for tick reproduction so that a large increase in population size may be expected to follow such rain.     

A survey of ticks (Acari: Ixodidae) on dairy cattle on the island of Menorca in Spain

A survey of ticks affecting dairy cattle under extensive management on Menorca island (off the Spanish Mediterranean coast) was performed through 1999-2000 on seven farms. The species collected were Rhipicephalus bursa, R. turanicus, Hyalomma m. marginatum, H. lusitanicum and Boophilus annulatus. The most abundant species were R. bursa and H. m. marginatum, with peaks of 10.7 (in summer) and 7.5 (in spring) ticks/cow, respectively. R. turanicus was scarcely encountered, while B. annulatus and H. lusitanicum were abundant only in a few localities. The mild climate and adequate vegetation on the island provide satisfactory habitat for extended periods of tick activity, as compared with other regions where these ticks have been collected. The competence of the ticks as vectors for pathogens and the difficulty of using acaricide treatments in the region are discussed.     

Natural occurrence of lethal aspergillosis in the cattle tick Rhipicephalus (Boophilus) microplus (Acari:Ixodidae)

The purpose of this study was to describe an unreported entomopathogenic fungus that naturally infects the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae). Engorged female ticks, showed symptoms of fungal infection after controlled tick infestation of cattle. Infected ticks developed a distinctive dark colour, a pale mould grew over the cuticle and the ticks eventually died covered with fungal conidiophores. The responsible fungus was isolated and cultured on mycological medium and submitted to microscopic morphology, biochemical phenotyping and 18S rRNA ribotyping analyses, which identified it as aflatoxin-producing Aspergillus flavus. Spores from the cultured fungus were experimentally sprayed over healthy engorged female ticks, obtaining an 80% prevalence of experimental infection of healthy ticks and their egg masses, the larval progeny after incubation under laboratory conditions was also infected. These results demonstrate that A. flavus is the causative agent of the natural fungal disease of the cattle tick R. microplus described here.     

The Susceptibility of Boophilus annulatus (Ixodidae) Ticks to Entomopathogenic Fungi

The pathogenicity of five species of entomopathogenic fungi (Deuteromycetes, species: Beauveria bassiana, Metarhizium anisopliae, Metarhizium flavoviride, Paecilomyces fumosoroseus and Verticillium lecanii ) to the various developmental stages of Boophilus annulatus ticks was compared under laboratory conditions. M. anisopliae and B. bassiana strains were most virulent to engorged females and caused 85-100% mortality within 7-10 days post-inoculation (PI). The highest mortality of engorged females caused by other fungi reached only 25-60%. All tested fungi prevented or reduced the egg laying capability of the ticks several days before their death. Females surviving after treatment with the most virulent M. anisopliae strain (Ma-7) reached only 7-8% of their egg laying capacity as compared with the control. Other fungi caused a reduction of the weight of laid eggs by 35.4-80.8% as compared with untreated females. Only M. anisopliae and B. bassiana strains caused 70-98% mortality of the treated eggs. Unfed larvae of Boophilus annulatus were sensitive to M. anisopliae and M. flavoviride strains. The Ma-7 strain was most virulent to unfed larvae, with a mortality rate of 80.4% at a concentration of 1 ×107 spores ml -1 and 100% mortality at a concentration of 1 ×108 spores ml -1 .     

Therapeutic and persistent efficacy of a single injection treatment of ivermectin and moxidectin against Boophilus microplus (Acari: Ixodidae) on infested cattle

The effectiveness of a single treatment with either ivermectin or moxidectin was determined by administering a single subcutaneous injection of each endectocide at 200 g per kg body weight to cattle infested with all parasitic developmental stages (adults, nymphs, and larvae) of Boophilus microplus (Canestrini). The percentage reduction in the number of females that reached repletion following treatment (outright kill) was 94.8 and 91.1% for ivermectin and moxidectin, respectively. In addition, the reproductive capacity of the females that did survive to repletion was reduced by >99%, regardless of the endectocide. Based on these two factors, the therapeutic level of control obtained against ticks on the cattle at the time of treatment was 99.0 and 99.1% for ivermectin and moxidectin, respectively. Engorged females recovered from either group of treated cattle weighed 3-times less than untreated females, and the egg masses produced by treated females weighed 5–8-times less than egg masses produced by untreated females. Partitioning of data into three separate 7-d post-treatment intervals allowed for an estimation of the efficacy of each endectocide against each individual parasitic development stage (adult, nymph, and larva). Results indicated that both endectocides were 99.7% effective against ticks that were in either the adult or nymphal stage at the time of treatment. However, the level of control against ticks in the larval stage of development at treatment was significantly lower at 97.9 and 98.4% for ivermectin and moxidectin, respectively. Analysis of the persistent (residual) activity of the two endectocides indicated that neither material provided total protection against larval re-infestation for even 1-wk following treatment. Against larvae infested 1–4 wk following treatment, the level of control with moxidectin ranged from 92.4% (1 wk) to 19.5% (4 wk). These control levels were higher at each weekly interval than for ivermectin, which ranged from 82.4% (1 wk) to 0.0% (4 wk). The potential for the use of these injectable endectocide formulations in the US Boophilus Eradication Program is discussed.This paper reports the results of research only. Mention of a commercial or proprietary product in this paper does not constitute an endorsement by the U.S. Department of Agriculture. In conducting the research described in this report, the investigators adhered to protocol approved by the USDA-ARS Animal Welfare Committee. The protocol is on file at the USDA-ARS, Knipling-Bushland U.S. Livestock Insects Laboratory, Tick Research Unit, Kerrville, TX. The U.S. Governments right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.This revised version was published online in May 2005 with a corrected cover date.     

Staphylococcus saprophyticus is a pathogen of the cattle tick Rhipicephalus (Boophilus) microplus

During experimental Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) infestation on cattle, approximately 5% of engorged female ticks showed symptoms of bacterial infection. The affected ticks were unable to oviposit, secreted a distinctive yellow exudate through the genital orifice and eventually died. Microscopic analysis of tick exudate showed abundant clusters of Gram-positive cocci bacteria that were isolated and cultured on bacteriological medium. Biochemical phenotyping and 16S rRNA ribotyping analysis on cultured bacteria identified it as Staphylococcus saprophyticus. This species was also isolated from healthy tick larvae, indicating that S. saprophyticus is commonly found in ticks during different developmental stages. However, conspicuous symptoms are only found on fully engorged females. Cultured S. saprophyticus induced identical pathological symptoms when the bacteria were experimentally inoculated into healthy ticks, demonstrating it to be the causative agent of the R. microplus infectious lethal disease described in this work.     

Efficacy of coumaphos applied as a dip for control of an organophosphorus-resistant strain of Boophilus microplus (Acari: Ixodidae) on cattle

The efficacy of coumaphos, an organophosphorus acaricide, was tested on a strain of Boophilus microplus (Canestrini) that was 9.5 times more resistant to the chemical than a susceptible strain. Cattle infested with larval, nymphal, and adult ticks were dipped into a vat charged at concentrations of 0.031, 0.083, 0.160, and 0.279% (AI). Assessment of efficacy was based on surviving tick numbers, female weight, egg mass weight, egg hatchability, and index of reproduction. At 0.031% (AI), the level of control was lower than the other coumaphos treatments, and the weight, fecundity, and fertility of surviving females was similar to untreated females, indicating only minimal adverse effects on the ticks. At 0.160 and 0.279% (AI), no differences in control, female weight, egg mass weight, or percentage egg hatch were observed, but effects were greater than that of untreated ticks or ticks treated at 0.031% (AI). At 0.083% (AI), most biological parameters were intermediate, but there was no difference in control compared with the 2 higher concentrations. Thus, even with the increase in concentration of more than 3 times between treatments of 0.083 and 0.279% (AI), there was no substantial increase in control. The residual efficacy of all 4 treatments showed that none provided complete protection against larval reinfestation for even 1 wk after treatment. Therefore, the presence of organophosphorus-resistant ticks at U.S. ports-of-entry could jeopardize the success of the Boophilus eradication program.     

Ecology and phenology of cattle ticks in Zambia: Development and survival of free-living stages

A study on development and survival of free-living stages of three important cattle ticks in Zambia,Amblyomma variegatum Fabricus,Boophilus decoloratus Koch, andRhipicephalus appendiculatus Neumann, was carried out to complement studies on seasonal dynamics of parasitic stages.Different instars of engorged ticks were exposed under quasi-natural conditions according to the season in which they occur naturally. Generally, development rates of all stages of the three species were related to temperature, whilst the duration of survival was influenced mainly by rainfall and consequent relative humidity.Observations on the effect of age and climate on the behaviour of ticks on pastures were also made. BothA. variegatum andR. appendiculatus completed only one generation per year. InA. variegatum, engorged females detaching early in the adult season (August to October) undergo morphogenetic diapause. Adults ofR. appendiculatus emerging between August and October enter a period of behavioural diapause before becoming active in December. These mechanisms effectively synchronize the life-cycles of these two univoltine species. The one-host tick,B. decoloratus, is able to complete three to five generations each year with no indication of seasonal synchronization.     

Ticks infesting domestic animals in northern Greece

The tick species infesting grazing animals in the countryside of 11 prefectures in Northern Greece were investigated during April-July and September-December of consecutive years 2003-2006. A total of 3,249 (1,952 males, 1,297 females) adult ticks were collected from goats, sheep, cattle and dogs. Ticks were identified as Ixodes ricinus (44.57%), Ixodes gibbosus (4.09%), Rhipicephalus bursa (19.14%), Rhipicephalus sanguineus, Rhipicephalus turanicus (5.79%), Hyalomma marginatum marginatum (12.40%), Dermacentor marginatus (0.31%) and Boophilus annulatus (4.43%). Rhipicephalus spp. and Hyalomma spp. were abundant in all prefectures, Ixodes spp. were present in 9/11 prefectures, Boophilus spp. in 4/11, while Dermacentor spp. were found only in one. Results of this study give an insight into the ecology of ticks and their potential of tick-borne diseases in the country.     

Mortality rate of adult ticks due to infection by entomopathogenic nematodes

The mortality of Boophilus annulatus, Hyalomma excavatum, Rhipicephalus bursa, and Rhipicephalus sanguineus adult ticks was recorded after their exposure in petri dishes to 5 entomopathogenic nematode strains. The strains used were DT and Mexican of Steinernema carpocapsae, Hb HP88 of Heterorhabditis bacteriophora, and IS-3 and IS-5 of Heterorhabditis sp. The most rapid killing rates (LT50 and LT90) were observed for B. annulatus ticks (0.8-5.0 days). Most unfed males died 0.3-2.8 days after the unfed females, whereas even more time (0.8-8.0 days) passed before engorged females died. In most bioassays, the IS-3 and IS-5 strains of Heterorhabditis sp. nematodes appear to be the most pathogenic for ticks and, in most cases, killed ticks several days before the other 3 nematode strains. Unfed adult ticks exposed to nematodes died within less time than it takes for adults to complete their prefeeding period after molting.     

Control of lone star ticks (Acari: Ixodidae) on Spanish goats and white-tailed deer with orally administered ivermectin

Ivermectin administered orally to Spanish goats, Capra hircus (L.), or to white-tailed deer, Odocoileus virginianus (Zimmerman), was highly effective against lone star ticks, Amblyomma americanum (L.). For Spanish goats, daily oral doses of 20 micrograms/kg resulted in greater than or equal to 2 ppb ivermectin in the blood. This level was sufficient to cause greater than 95% reduction of estimated larvae from feeding ticks. A bioassay with horn flies, Haematobia irritans (L.), was developed to estimate oral intake of ivermectin. Probit analysis of dose-mortality data indicated that a 50% reduction in adult horn fly emergence can be expected when the manure from goats treated orally with ivermectin at 10, 20, 35, and 50 micrograms/kg/d was mixed with untreated cow manure at a rate of 0.345, 0.110, 0.100, and 0.092%, respectively. In studies with white-tailed deer, daily oral doses of 35 and 50 micrograms/kg/d provided 100% control of adult and about 90% control of nymphs that were placed on treated fawns. A single oral dose of 50 micrograms/kg gave greater than 90% control of adult and nymphal ticks attached to treated fawns at the time of drug administration and 70% control of ticks placed on treated deer three days thereafter. When ticks were placed on fawns treated with a single dose of ivermectin (50 micrograms/kg) the engorgement period was longer, ticks were lighter in weight, and females laid fewer eggs than ticks detaching from control fawns. A single oral dose of ivermectin at 20 micrograms/kg prevented about 60% of the adult and nymphal ticks attached at the time of drug administration from engorging, but did not affect other ticks placed on the animals after treatment.