Search

As part of the Northeast Area-wide Tick Control Project (NEATCP), meta-analyses were performed using pooled data on the extent of tick-vector control achieved through seven concurrent studies, conducted within five states, using U.S. Department of Agriculture "4-Poster" devices to deliver targeted-acaricide to white-tailed deer. Although reductions in the abundance of all life-stages of Ixodes scapularis were the measured outcomes, this study focused on metrics associated with I. scapularis nymphal tick densities as this measure has consistently proven to directly correlate with human risk of acquiring Lyme disease. Since independent tick sampling schemes were undertaken at each of the five environmentally distinct study locations, a meta-analytic approach permitted estimation of a single true control-effect size for each treatment year of the NEATCP. The control-effect is expressed as the annual percent I. scapularis nymphal control most consistent with meta-analysis data for each treatment year. Our meta-analyses indicate that by the sixth treatment year, the NEATCP effectively reduced the relative density of I. scapularis nymphs by 71% on the 5.14 km(2) treatment sites, corresponding to a 71% lower relative entomologic risk index for acquiring Lyme disease.

Amitraz, a formamidine acaricide, plays an important role in the control of the southern cattle tick, Boophilus microplus (Canestrini), and other tick species that infest cattle, dogs, and wild animals. Although resistance to amitraz in B. microplus was previously reported in several countries, the actual measurement of the level of amitraz resistance in ticks has been difficult to determine due to the lack of a proper bioassay technique. We conducted a survey, by using a newly reported technique that was a modification of the standard Food and Agriculture Organization larval packet test, to measure the levels of resistance to amitraz in 15 strains of B. microplus from four major cattle-producing states in Mexico. Low-order resistance (1.68- to 4.58-fold) was detected in 11 of those strains. Our laboratory selection using amitraz on larvae of the Santa Luiza strain, which originated from Brazil, achieved a resistance ratio of 153.93 at F6, indicating the potential for high resistance to this acaricide in B. microplus. Both triphenylphosphate and piperonyl butoxide significantly synergized amitraz toxicity in both resistant and susceptible tick strains. Diethyl maleate synergized amitraz toxicity in one resistant strain but had no effect on the susceptible strain and had minor antagonistic effects on two other resistant strains. Target site insensitivity, instead of metabolic detoxification mechanisms, might be responsible for amitraz resistance observed in the Santa Luiza strain and possibly in other amitraz resistant B. microplus ticks from Mexico. The Santa Luiza strain also demonstrated high resistance to pyrethroids and moderate resistance to organophosphates. Multiple resistance shown in this strain and other B. microplus strains from Mexico poses a significant challenge to the management of B. microplus resistance to acaricides in Mexico.

Toward the end of the nineteenth century a complex of problems related to ticks and tick-borne diseases of cattle created a demand for methods to control ticks and reduce losses of cattle. The discovery and use of arsenical solutions in dipping vats for treating cattle to protect them against ticks revolutionized tick and tick-borne disease control programmes. Arsenic dips for cattle were used for about 40 years before the evolution of resistance of ticks to the chemical, and the development and marketing of synthetic organic acaricides after World War II provided superior alternative products. Most of the major groups of organic pesticides are represented on the list of chemicals used to control ticks on cattle. Unfortunately, the successive evolution of resistance of ticks to acaricides in each chemical group with the concomitant reduction in the usefulness of a group of acaricides is a major reason for the diversity of acaricides. Whether a producer chooses a traditional method for treating cattle with an acaricide or uses a new method, he must recognize the benefits, limitations and potential problems with each application method and product. Simulation models and research were the basis of recommendations for tick control strategies advocating approaches that reduced reliance on acaricides. These recommendations for controlling ticks on cattle are in harmony with recommendations for reducing the rate of selection for acaricide resistance. There is a need to transfer knowledge about tick control and resistance mitigation strategies to cattle producers.

Objective: To evaluate the efficacy of coumaphos, an organophosphate (OP) acaricide, at concentrations up to 2 times higher than the highest concentration required by the US Eradication Program against all stages of an OP-resistant strain of Boophilus microplus in experimentally infested cattle., Animals: 16 tick-naïve 200-kg female Hereford calves., Procedure: Four groups of cattle (4 calves/group) were all infested with Boophilus ticks 3 times before treatment. Each group was treated with coumaphos as follows: group 1, at 0.165% active ingredient (AI); group 2, at 0.299% AI; group 3, at 0.566% AI; and group 4, not treated. Following treatment, ticks were collected for 21 days. Ticks collected 1 to 7, 8 to 14, and 15 to 21 days after treatment were considered adults, nymphs, and larvae, respectively, at time of treatment., Results: Overall control at 0.165, 0.299, and 0.566% AI was 52.9, 75.8, and 89.7%, respectively. Control of adults ranged from 4.3% at 0.165% AI to 73.5% at 0.566% AI. Control of nymphs ranged from 60.6% at 0.165% AI to 97.3% at 0.566% AI. Control of larvae was > 98% at all coumaphos concentrations., Conclusions and Clinical Relevance: All coumaphos concentrations failed to provide acceptable control for use in the US Eradication Program against OP-resistant ticks. Treatment was least effective against adults and most effective against larvae. Even at 0.566% AI (2 times higher than required by the US Eradication Program), ticks were not eradicated, placing the United States at risk from dispersing cattle harboring viable ticks to uninfested areas.

Exotic tick species and tick-borne diseases are serious threats to live-stock, companion animals, and wildlife in the United States. Recurring introductions of exotic tick species into the United States are a significant indicator of the degree of risk. Successful tick-eradication campaigns, such as the national program that eradicated Boophilus annulatus and B. microplus from the United States, the Cattle Fever Tick Eradication Program of the US Department of Agriculture's Veterinary Services that protects against the re-entry and dissemination of Boophilus ticks from Mexico back into their former haunts in the southern states, and the eradication action that eliminated Rhipicephalus evertsi from a game park in Florida, are sources of useful information that aid in elucidating essential elements of successful eradication programs. Examples of failed eradication programs in places such as Puerto Rico and St. Croix also have heuristic value. Among the varieties of tick species and related infectious agents that threaten the United States, Boophilus ticks and bovine babesiosis, Amblyomma species (especially the tropical bont tick) and heartwater, and equine babesiosis, for which endemic vectors exist, are of special concern. Risk assessments to accumulate, evaluate, and synthesize information needed to appraise risks, consequences, and preparedness are necessary not just to inform federal, state, and local officials, as well as producers and stakeholders, but also to facilitate the creation of emergency response plans.

The efficacy of pour-on formulations of three macrocyclic lactone endectocides (moxidectin, ivermectin, and eprinomectin) was evaluated on cattle against Boophilus microplus (Canestrini) using two different treatment regimes. A single application treatment regime with each endectocide showed that fewer ticks per calf were recovered from all treated calves than from untreated cattle, but the level of control among the three treatments was similar (range; 78.7-87.7%) against all stages of ticks on the calves at the time of treatment. The engorged female and egg mass weights of all treated ticks were less than that of untreated ticks. Among the treated groups, the ivermectin and eprinomectin-treated females weighed less and produced lower weight egg masses than those from moxidectin-treated cattle. In a double application treatment regime with a 4-d interval between treatments, there were fewer ticks per calf recovered from the treated cattle than from untreated cattle. In addition, all treated females weighed less and produced lower weight egg masses than those from untreated cattle. Control with moxidectin (90.3%) was lower than with either ivermectin (98.9%) or eprinomectin (99.7%). The mean female and egg mass weight of the ivermectin and eprinomectin-treated groups was also less than that of the moxidectin treatment. A single application treatment against either 18- or 20-d-old adult ticks indicated that both moxidectin and ivermectin were less effective against 20-d-old ticks that were nearer to completing their parasitic development on the animal. In contrast, eprinomectin was the only endectocide tested that was equally effective against both 18- and 20-d-old ticks.

We utilized RNA Northern blot analysis and ribonuclease protection assays (RPA) to study the mRNA expression level of a putative carboxylesterase-encoding gene from several strains of Boophilus microplus (Canestrini). Both the Northern analysis and RPAs indicated that an esterase transcript was more abundant in the pyrethroid resistant strain, Coatzacoalcos (Cz), compared to a susceptible control strain and a resistant strain whose pyrethroid resistance is mediated through a target site insensitivity mechanism. A PCR-based assay was designed to identify the presence of a previously reported point mutation in this B. microplus esterase gene. The reported G-->A substitution at nucleotide 1120 creates an EcoR I site in the mutant allele which can be detected by EcoR I digestion of the amplification products. The PCR assays showed that the frequency of the mutant allele was highest in the Cz-resistant strain, which has been shown to have an esterase-mediated resistance mechanism. The PCR assay can be performed either on individual tick larvae or hemolymph from adults.

Rhipicephalus sanguineus (Latreille) were collected from the Corozal Army Veterinary Quarantine Center in Panama and characterized for resistance to five classes of acaricides. These ticks were highly resistant to permethrin, DDT, and coumaphos; moderately resistant to amitraz; and not resistant to fipronil when compared with susceptible strains. Resistance to both permethrin and DDT may result from a mutation of the sodium channel. However, synergist studies indicate that enzyme activity is involved. The LC50 estimate for permethrin was lowered further in the Panamanian strain then in susceptible strains with the addition of triphenylphosphate (TPP), but not with the addition ofpiperonyl butoxide (PBO). This suggests that esterases and not oxidases are responsible for at least some pyrethroid resistance. Elevated esterase activity and its inhibition by TPP were confirmed by native gel electrophoresis. The LC50 estimate obtained for coumaphos in the Panamanian strain was not lowered further than what was observed for susceptible strains by the addition of TPP or PBO. This indicates that enzyme activity might not be involved in coumaphos resistance. Resistance to amitraz was measured through a modification of the Food and Agriculture Organization Larval Packet Test. All tick strains were found to be susceptible to fipronil.

White-tailed deer treated themselves with a commercial pour-on acaricide formulation containing 2% amitraz as they fed from an ARS-patented '4-poster' topical treatment device. Whole kernel corn attracted deer to a single device placed in each of two deer-fenced pastures. In the treatment pasture, the rollers of the treatment device were charged with the acaricide, whereas the rollers of the device in the other pasture remained untreated. Deer were allowed to use the '4-posters' during periods of tick activity beginning in early to midspring and lasting through late summer to early fall for three consecutive years. Pretreatment sampling of adults and nymphs with dry-ice traps and larval masses with flip cloths showed no significant differences in population indices between the two pastures; however, after the third year of treatment, control of nymphal and adult ticks in the treated pasture was 91.9 and 93.7%, respectively, when compared with the untreated pasture. Control of larval masses increased from 68.4% in year 1 to 96.4% in year 2, but declined to 88.0% in year 3, probably because of the presence of feral hogs. This study demonstrated that application of amitraz to white-tailed deer through free-choice interaction with a '4-poster' device significantly reduced the abundance of free-living lone star ticks in a deer-fenced experimental pasture. Moreover, the yearly pattern of incremental increases in control and the final percentage control values for all three parasitic life stages in this topical application study were similar in magnitude to that observed in a previously conducted study in which the systemic acaricide ivermectin was used to reduce populations of free-living ticks by controlling ticks on deer.

Two esterase cDNA sequences were obtained from susceptible and organophosphorus resistant strains of Boophilus microplus. Both sequences have a high degree of homology to carboxylesterase B. One gene has identical sequences in both strains and the other showed two point mutations. One mutation produces an amino acid substitution when the amino acid sequence is deduced, this mutation was detected in six different populations susceptible and resistant to insecticides, but a pyrethroid resistant strain was the only one that showed only the mutant allele. Identification of this mutation and the strong signal detected in southern blot with this strain, suggest that esterases are contributing to detoxification of pyrethroid compounds, as a resistant mechanism in Mexican strains of the southern cattle tick.

A '4-poster' device that attracts white-tailed deer to a bait source, and as they feed, allows a self-application of a pesticide to the head, ears, and neck to control ticks was designed, constructed, and tested. The device consists of a central bin containing bait to attract deer and two feeding and application stations. These stations each have one bait port and two vertical pesticide-impregnated applicator rollers. This design allows unrestricted vertical retraction of the head to minimize injury to the deer or damage to the posts supporting the pesticide application rollers. Observations using deer demonstrated ready acceptance and repeated use by both antlered and antlerless deer. Results of an initial trial indicate that control values for lone star ticks, Amblyomma americanum (L.), exceeded 92-97% on deer that used the device regularly.

Arsenic dips were the first effective method for controlling ticks and tick-borne diseases, and were used in many parts of the world for over 50 years before resistance to the chemical became a problem. Until organochlorine products became available about 1946 as alternatives to arsenic, significant losses occurred in cattle herds exposed to arsenic-resistant tick strains. Since the discovery of organochlorines, virtually every chemical group of pesticides developed for the control of arthropods is represented among the list of products employed for the control of ticks on cattle. The evolution of tick resistance to acaricides has been a major determinant of the need for new products. The variety of procedures for treating animals with acaricides ranges from dipping cattle to injecting systemic acaricides, but regardless of the treatment method used, producers need to know and follow proper application procedures to derive maximum benefits. The possibility of stocking with cattle breeds that acquire pronounced resistance to ticks or using recombinant antigen antitick vaccines are the most promising alternatives to acaricides. Most ranchers depend completely on acaricides to control ticks, but do not have access to guidelines on how to make a profit from their tick control program or how to detect and resolve problems with resistance to acaricides. Extension programs are needed to help ranchers manage animal health problems, including how to control ticks and tick-borne diseases.

Using a strategy based on degenerate primers derived from acetylcholinesterase (AChE) from other species, we cloned and sequenced a putative AChE cDNA from the southern cattle tick, Boophilus microplus (Canestrini). The sequence has a high degree of homology to sequences of AChE from other species reported in the GenBank. The open reading frame of 1,689 bp, corresponding to a deduced sequence of 563 amino acids, has conserved regions and features shared by the AChE family, necessary for its catalytic activity. No differences were found in the putative cDNA sequences from organophosphorus acaricide (OP) resistant and susceptible strains. The results suggest that this putative AChE gene is not involved in resistance to OP compounds as a mutated gene in the resistant strain studied. However, differences were detected, with a probe derived from this cDNA, in DNA fragments after digestion of genomic DNA from different strains with restriction nucleases. This indicates polymorphism in this gene in B. microplus.

Using reverse transcription polymerase chain reaction and degenerate oligonucleotide primers, a partial para-homologous sodium channel cDNA was obtained from the southern cattle tick, Boophilus microplus (Canestrini). The cDNA sequence encoded the region in which knockdown resistance (kdr)-type mutations have been identified in numerous insect species. Comparison of deduced amino acids from the cDNA sequence showed high similarity with sodium channels from other species, particularly in highly conserved repeat domains of the sodium channel. Analysis of the kdr-homologous region of the genomic DNA sequences from several susceptible and pyrethroid-resistant tick strains did not detect mutations. The result suggests novel mutations in the sodium channel gene or metabolic detoxification may be involved in the resistance to pyrethroids in this tick.

Two patterns of pyrethroid resistance were characterized from Boophilus microplus (Canestrini) collected in Mexico. One was characteristic of a kdr mutation and the other involved esterase and cytochrome P450 enzyme systems. Very high resistance to permethrin, cypermethrin, and flumethrin, not synergized by TPP and PBO and high resistance to DDT, characterized the kdr-like pattern found in the Corrales and San Felipe strains. Esterase and cytochrome P450-dependent resistance was found in the Coatzacoalcos strain. It was characterized by resistance to permethrin, cypermethrin, and flumethrin, synergized by TPP and PBO, but no resistance to DDT. The Coatzacoalcos strain also showed 3.6-fold resistance to the organophosphate coumaphos. This factor appeared to be independent of pyrethroid resistance. Pyrethroid resistance patterns found in Mexico were similar to those found earlier in Australia. The significance of pyrethroid and coumaphos resistance to the U.S. cattle fever tick quarantine is discussed.

To investigate the molecular mechanism of resistance to pyrethroids in the southern cattle tick, Boophilus microplus, we have obtained and sequenced a partial para-homologous sodium channel cDNA from susceptible and pyrethroid-resistant tick strains. A point mutation that results in an amino acid change from Phe to Ile was identified in the highly conserved domain IIIS6 of the homologous sodium channel from ticks that are highly resistant to pyrethroid acaricides. This mutation is at a location different from those reported in the same gene in pyrethroid-resistant insects., (Copyright 1999 Academic Press.)

A glutathione S-transferase (GST) was purified from the larval cattle tick, Boophilus microplus (Acari: Ixodidae), by glutathione-affinity chromatography. The purified enzyme appeared as a single band on SDS-PAGE and has a molecular mass of 25.8 kDa determined by mass spectrometry. The N-terminus of the purified enzyme was sequenced. The full-length cDNA of the enzyme was isolated by RT-PCR using degenerate oligonucleotides derived from the N-terminal amino acid sequence. The cDNA contains an open reading frame encoding a 223-amino-acid protein with the N-terminus identical to the purified GST. Comparison of the deduced amino acid sequence with GSTs from other species revealed that the enzyme is closely related to the mammalian mu class GST.

A strain of Boophilus microplus (Canestrini) was selected fro resistance to permethrin by pressuring larvae with increasing doses (range, 0.05-0.35% [AI]) through successive generations (generations F2-F7). At the beginning of the selection process (F2), the pyrethroid resistant (PR) strain was 5.4 times more resistant to permethrin than the pyrethroid susceptible (PS) strain, and the level of resistance increased in each successive generation of the PR strain, reaching a resistance factor (resistance factor) of 20.9 in the F7 generation. Thus, in only 5 generations the level of resistance in the PR strain was increased by 4-fold. The efficacy of permethrin was evaluated by dipping cattle infested with the PS strain and cattle infested with the F7 generation of the PR strain in a vat at 0.057% (AI) (Coopers Animal Health, Mundelein, IL; recommended concentration). Evaluation of the PS strain showed that untreated cattle produced significantly (P < 0.05) more females with a higher index of reproduction than treated cattle. Additionally, biological factors (female weight, egg mass weight, and percent egg hatch) associated with the untreated females were all significantly (P < 0.05) greater than treated females. Conversely, results obtained from the PR strain showed that tick numbers, index of reproduction value, and biological parameters of females in the untreated group were not significantly different (P > 0.05) from those of the treated group. The overall control achieved in the PS strain (99.2%) was significantly higher (P < 0.05) than that of the PR strain (35.7%). The results of the study as they relate to the United States Boophilus Eradication Program are discussed.

The conventional method of identifying acaricide resistance in a suspect tick population by the United Nations Food and Agriculture Organization packet assay is a laborious and time-consuming process. DNA probes have been demonstrated as rapid and accurate tools for detecting pesticide resistance in insect species. Random-amplified polymorphic DNA (RAPD) has been used by other groups to differentiate species of mosquitoes and populations within a mosquito species. By using different arbitrary oligonucleotides as primers with RAPD, we have demonstrated that various strains of Boophilus microplus (Canestrini) show different patterns of DNA fragments on agarose gel electrophoresis. The unique DNA fragments may be useful for developing probes that can detect acaricide resistance in field pest populations.

A bimodal, diurnal rhythm of detachment was observed for engorged female Boophilus annulatus fed on Hereford heifers confined in individual stalls in an open-sided barn and exposed to ambient climate and light. In 3 experiments during which hosts were fed each morning and evening, a morning period of increased detachment activity occurred during a 6-h period centered around the 2-h collecting interval in which sunrise occurred. A 2nd peak of activity occurred during the 2-h interval that began 6-8 h later. Seventy-four to 84% of the total detachment occurred during these two 6-h intervals and most of the detachment (44-62%) occurred during the afternoon period. These experiments were done in July, September, and January when daylengths were 13 h, 27 min; 12 h, 22 min; and 10 h, 37 min, respectively. In a 4th experiment in which groups of hosts were fed at different times of the day, maximal percentages of 41.5 and 38.3 of the total detachment from morning-fed or both morning and evening-fed heifers, respectively, occurred during the 2-h interval in which the sun rose instead of during the evening. During the evening peak period, the number of engorged females that detached from these 2 groups of heifers was approximately 1/3-1/4 the number that detached during the peak period in the morning. In contrast, 43.6% of the engorged females in the evening-fed group detached during an 8-h morning period of increased detachment activity that began in the interval between 0200 and 0400 hours. About the same percentage of the ticks (38.5) detached during a 6-h period that began at 1400 hours. The less precisely delimited pattern of detachment of engorged females from cattle fed only in the evening, as contrasted with the rhythm observed for ticks that detached from heifers fed in the morning or both morning and evening, indicates that the nutritional or physiological state of the host may influence the rhythm exogenously. Whether the morning or evening peak of detachment activity is dominant is a question that remains unresolved.

Cattle infested with all parasitic life-stages of Boophilus microplus (Canestrini) were treated once with a pour-on formulation of fipronil at 0.25, 0.5, or 1.0% active ingredient (AI) to determine the therapeutic efficacy. Additionally, cattle were infested at weekly intervals for 13 consecutive weeks after treatment to determine the persistent effectiveness of the three concentrations. Results of therapeutic efficacy of fipronil showed that with each increase in concentration there was a corresponding and often significant (P < 0.05) decrease in the numbers, fecundity and fertility of engorged females. The overall control of the Index of Reproduction (IR) achieved at 0.25 and 0.5% AI was 86.2 and 94.3%, respectively, while the control of the IR at the 1.0% AI concentration was 99.7%. The persistent efficacy of fipronil, like the therapeutic efficacy, was also dose related. The 0.25% AI treatment failed to provide complete protection (100%) against larval reinfestation, although control of the IR remained high (> 95%) for the first 6 weeks after treatment. In contrast, at 0.5% AI the control of the IR remained at 100% for the first 4 weeks after treatment, and was > 90% for an additional 2 weeks (6 weeks posttreatment). The 1.0% AI concentration afforded the longest residual activity, providing virtually 100% protection against larval reinfestation for 8 weeks after treatment was applied. Based on the results, neither the 0.25 or 0.5% AI concentration completely eliminated the immature stages of the tick (nymphs and larvae) on the host at the time of treatment (therapeutic efficacy), and the residual activity (persistent efficacy) did not prevent reinfestation by larvae for long periods after treatment. While the 1.0% AI concentration provided both therapeutic and residual efficacy that would be suitable for use in the eradication program, caution is still warranted because a few engorged females detached for up to 25 days after treatment, although none reproduced after the 6th day.

Selection of lone star ticks, Amblyomma americanum (L.), that were reared in the laboratory under short-day photoperiods of 10:14 (L:D) h resulted in third generation (F3) diapause versus F3 nondiapause strain replete nymphs having significantly different mean molting times (days from detachment to ecdysis) of 100.9 versus 54.7 d, respectively; whereas, the F7 unselected laboratory control strain had an even smaller, significantly different mean molting time of 49.5 d. Two hybrid crosses of F2 nondiapause male with F2 diapause female ticks and F2 nondiapause female with F2 diapause male ticks yielded intermediate replete nymphal mean molting times of 62.0 and 68.9 d, respectively. All strains retained the ability to develop rapidly under long-day photoperiodic conditions of 14:10 (L:D) h, although F3 nondiapause strain ticks also exhibited reduced fitness, especially when exposed to the long-day stimuli. Analyses of molting times used as phenotypic values indicate that this diapause trait is incompletely dominant, and these and other observations indicate that inheritance of photoperiodically induced prolonged replete nymphal molting times is polygenic in this species.

Offspring of Amblyomma americanum (L.) reared for four generations in a 12:12 (L:D) photoperiod in the laboratory were held in 10:14 (L:D) conditions and bred to select for developmental diapause (DIA) or nondiapause (NON) characteristics for two additional generations. Sequential generations of fed DIA nymphs had mean molting times (days from detachment to ecdysis) that were 8.0% (DIA1) and 35.7% (DIA2) greater than parental ticks, and maximal development time was extended by 20% in DIA2 ticks over that of parentals. Selection in NON strains resulted in a significant decrease of detachment to ecdysis times in NON1 ticks, but the detachment to ecdysis times in NON2 ticks increased and was not different from parental ticks. Breeding for DIA and NON extremes did not affect the ability of either strain to develop rapidly if held in long-light (14:10 [L:D]) conditions. Selection for DIA resulted in extension of the period from detachment of fed nymphs to preapolysial posturing rather than from posturing to ecdysis of adults.

When Boophilus microplus and Type-II hybrids (B. microplus females X B. annulatus males) were released simultaneously onto bovine hosts, mating between the two forms appeared not to be at random. There were more contypic and fewer intertypic matings than predicted under an assumption of panmixia. An examination of the patterns of matings revealed that more of the matings on the first two days of detachment were between the two sexes of B. microplus. Engorged females dropping on the last four days of maximum female detachment were predominantly hybrids mated to both B. microplus and hybrid males. The non-random mating pattern does not appear to be caused by assortative mating between B. microplus and Type-II hybrids, but because the B. microplus were competent to mate two days before the hybrids and the B. microplus males compete for males of both types better than the Type-II males.

Progeny of Dermacentor andersoni Stiles adults collected from one "montane" and two "prairie" sites in southern Alberta, Canada, were exposed to combinations of 9:15, 11:13 and 13:11 (L:D) daily photoperiods during various stages of their life cycle. Time required for developmental and reproductive events was recorded. Significant differences in mean molting times of fed larvae were observed, yet the differences were small, and mean times were not attributed to photoperiodic regime. Fed nymphal "prairie" ticks had significantly longer developmental rates under decreasing light regimes than in constant or increasing regimes, while "montane" ticks showed no differential response to any of these regimes. Engorged "montane" females in all regimes weighed significantly more than those in either "prairie" strain, and "prairie" strain females in increasing and constant short-day regimes were significantly heavier than those in decreasing and constant long-day regimes. Photoperiod is unimportant in the regulation of fed-larval development, and the magnitude of female engorgement may be nominally favored by short-day and increasing regimes. The differential phenotypic expression of photoperiodic regulation of fed nymphal development in this tick may have resulted from selective pressures involving differences in host availability and moisture conditions in the two geographic regions.

Four natural populations and 4 laboratory colonies of Boophilus microplus (Canestrini) and a laboratory colony of Boophilus annulatus (Say) were subjected to electrophoretic analysis to determine levels of genetic similarity and genetic variability. Populations of B. microplus exhibited high genetic similarity (I = 0.984 +/- 0.012) indicating that all populations share a relatively undifferentiated gene pool. Host vagility is proposed as an important mechanism promoting gene flow in ectoparasites. Levels of genetic variability for B. microplus (h = 0.092 +/- 0.008; P = 0.330 +/- 0.050) were within levels reported for other arthropods. The average genetic identity of 0.716 +/- 0.013 between B. microplus and B. annulatus is of a level characteristic of sibling species. Diagnostic isozymes between laboratory colonies will facilitate identification of these morphologically similar species.

The ability of guinea pigs to acquire resistance to Dermacentor andersoni and Amblyomma americanum was determined by repeatedly infesting separate sets of guinea pigs with tick larvae. Resistance was measured in terms of reduced numbers successfully engorging and reduced weight of those ticks that engorged. An 83% reduction in numbers of larvae engorging and a 64.5% reduction in the weight of engorged larvae were seen between the first and second infestations with D. andersoni. Guinea pigs exhibited considerably less resistance to A. americanum the third time they were exposed to this species than did guinea pigs infested twice with D. andersoni. Feeding success was only 30.8% less than the initial percentage that engorged, and the percentage weight reduction was 35. During the challenge infestations, sizable fluid-filled vesicles formed on ears of the guinea pigs used as hosts for D. andersoni or A. americanum. Cross-resistance was evaluated by dividing D. andersoni-resistant animals into groups and challenging them with D. andersoni D. variabilis, A. americanum, or Ixodes scapularis. Appreciable cross-resistance was apparent between the two Dermacentor species. The weights of the A. americanum and I. scapularis were significantly reduced, but not the number that engorged. When A. americanum-resistant guinea pigs were challenged, they were cross-resistant to D. variabilis but not to D. andersoni. Skin tests on guinea pigs in which extracts of tick salivary glands were used as the antigens did not conclusively reflect the same patterns of cross-reactions noted in the tests of cross-resistance.

White-tailed deer (Odocoileus virginianus L.) were evaluated as an alternate host for the cattle fever tick, Boophilus annulatus (Say). The total of adult female ticks recovered and associated reproductive parameters were compared between deer and bovine hosts. Significantly fewer ticks were recovered from deer than from cattle; this was attributed to the grooming behavior of the deer. The mean weight of ticks taken from deer (243.5 mg) was significantly less than that of ticks recovered from cattle (344.5 mg) with about 15% of the ticks from deer prematurely detached. Egg mass weight from the ticks recovered from deer (129.4 mg) was significantly less than that of ticks from cattle (172.1 mg). A significant difference was observed between the percentage hatch of the eggs of ticks from deer (63.1%) and ticks from cattle (76.7%). The index of reproduction was about 20 times greater for the ticks from the cattle than for the ticks from the deer. When the larval progeny of the ticks recovered from deer were reared on cattle, significantly fewer adult females were recovered than when larvae of ticks recovered from cattle were reared on cattle. This indicates a possible reduction in viability. All other parameters were comparable between the two groups. Thus, deer are biologically suitable hosts for B. annulatus, but significantly fewer ticks complete engorgement and those that complete engorgement have reduced fecundity.

A new arbovirus was isolated from Texas, U.S.A., populations of the Cliff Swallow parasits Argas (Argas) cooleyi Kohls and Hoogstraal, 1960. The virus, named Sunday Canyon, is serological urelated to any of 185 arbovirus strains or 20 other viral agents with which it was compared. Morphologically it resembles Bunyamwera viruses and, in common with them, is sensitive to lipid solvents and acid pH, and apparently possesses RNA. Although considerably resistant to a temperature of 41.5 degrees C, it rapidly loses infectivity when incubated at 56 degrees C. It is lethal for newborn white mice and infective for the Vero and Antheraea eucalypti cell lines. Sundays Canyon virus is the second tick-associated, Bunyamwera virus-like agent known from North America and the third virus to be reported from A. cooleyi in Texas.

Ovicidal activity of coumaphos, diazinon, dioxathion, chlorpyrifos, and crotoxyphos applied topically at 0.125, 0.25, and 0.5% (AI) to 1-d-old, 10-d-old, and 20-d-old eggs of southern cattle tick, Boophilus microplus (Canestrini), was determined. All acaricides produced some disruption of hatching of eggs in all age classes. Coumaphos, diazinon, dioxathion, and chlorpyrifos were most effective in reducing egg hatch of 1-d-old eggs but had little effect against 10- or 20-d-old eggs. Although crotoxyphos was comparable with other acaricides in reducing hatch in 1-d-old eggs, it caused significantly greater mortality (greater than or equal to 94.6%) in 20-d-old eggs than other compounds tested. Crotoxyphos applied at 0.5% (AI) is the only acaricide tested that provided sufficient ovicidal activity in all three egg age classes (greater than or equal to 85% reduction of hatch).

This paper describes an inexpensive, space-saving, and labor-efficient method for housing and making repeated observations of individual ticks held under specific photoperiodic, temperature, and humidity conditions. Using 96-well assay plates to house ticks, various developmental parameters, sex, survival, etc., of several thousand individual ticks can be recorded routinely in less than 1 hr. This design also permits more than 3,500 individual ticks to be maintained in 1 small (18.9-L) aquarium that serves as a humidity chamber. A small, unilluminated constant temperature incubator was converted inexpensively into a light and temperature programmable unit to contain the aquarium by adding a timing system, light fixture, and a second thermostat.