Search

The presence or absence of the biting midge Culicoides sonorensis Wirth & Jones (Diptera: Ceratopogonidae), a primary vector of bluetongue viruses (genus Orbivirus, family Reoviridae, BTV) in North America, was assessed on ranches and farms across the Northern Great Plains region of the United States, specifically Nebraska, South Dakota, and North Dakota, as part of a 2-yr regional study of BTV exposure among cattle. Blacklight/suction trap samples totaling 280 2-night intervals were taken at 140 aquatic sites (potential larval habitat for C. sonorensis) on 82 livestock operations (ranches and farms) that span a south-to-north gradient of expected decreasing risk for exposure to BTV. In Nebraska, C. sonorensis populations were common and widespread, present at 15 of 18 operations. Of 32 operations sampled in South Dakota, seven of which were sampled in successive years, 18 were positive for C. sonorensis; 13 of 14 operations located west of the Missouri River were positive, whereas 13 of 18 operations east of the river were negative. Of 32 operations sampled in North Dakota, seven of which were sampled both years, 12 were positive for C. sonorensis. Six of eight operations located west and south of the Missouri River in North Dakota were positive, whereas 18 of 24 operations east and north of the river were negative for C. sonorensis. These data illustrate a well-defined pattern of C. sonorensis spatial distribution, with populations consistently present across Nebraska, western South Dakota, and western North Dakota; western South Dakota, and North Dakota encompass the Northwestern Plains Ecoregion where soils are nonglaciated and evaporation exceeds precipitation. In contrast, C. sonorensis populations were largely absent east of the Missouri River in South Dakota and North Dakota; this area comprises the Northwestern Glaciated Plains Ecoregion and Northern Glaciated Plains Ecoregion where surface soils reflect Wisconsinan glaciation and precipitation exceeds evaporation. In defining a well-demarcated pattern of population presence or absence on a regional scale, the data suggest that biogeographic factors regulate the distribution of C. sonorensis and in turn BTV exposure. These factors, ostensibly climate and soil type as they affect the suitability of larval habitat, may explain the absence of C. sonorensis, hence limited risk for exposure to BTV, across the eastern Northern Plains, upper Midwest, and possibly Northeast, regions of the United States.

The authors developed a monitoring and risk mapping system using normalized difference vegetation index (NDVI) times series data derived from the advanced very high resolution radiometer (AVHRR) instrument on polar orbiting national oceanographic and atmospheric administration (NOAA) satellites to map areas with a potential for a Rift Valley fever (RVF) outbreaks in sub-Saharan Africa. This system is potentially an important tool for local, national and international organisations involved in the prevention and control of animal and human disease, permitting focused and timely implementation of disease control strategies several months before an outbreak. We are currently developing a geographic information system (GIS)-based remotely sensed early warning system for potential RVF vectors in the United States. Forecasts of the potential emergence of mosquito vectors will be disseminated throughout the United States, providing several months' warning in advance of potentially elevated mosquito populations. This would allow timely, targeted implementation of mosquito control, animal quarantine and vaccine strategies to reduce or prevent animal and human disease.

West Nile virus (Flaviviridae: Flavivirus) is a serious infectious disease that recently spread across the North America continent. A spatial analysis tool was developed on the ArcMap 9.x platform to estimate potential West Nile virus activity using a spatially explicit degree-day model. The model identifies when the virus Extrinsic Incubation Period (EIP) is completed within the vector longevity during mid-summer months. The EIP is treated as a threshold indicator of the potential for virus emergence and activity. Comparing the number of West Nile virus cases in Wyoming reported from 2003 to 2005 with model results, actual cases and predicted events of West Nile virus activity match relatively well. The model represents a useful method for estimating potential West Nile virus activity in a large spatial scale.

Potential larval habitats of the mosquito Culex tarsalis (Coquillett), implicated as a primary vector of West Nile virus in Wyoming, were identified using integrated remote sensing and geographic information system (GIS) analyses. The study area is in the Powder River Basin of north central Wyoming, an area that has been undergoing a significant increase in coalbed methane gas extractions since the late 1990s. Large volumes of water are discharged, impounded, and released during the extraction of methane gas, creating aquatic habitats that have the potential to support immature mosquito development. Landsat TM and ETM+ data were initially classified into spectrally distinct water and vegetation classes, which were in turn used to identify suitable larval habitat sites. This initial habitat classification was refined using knowledge-based GIS techniques requiring spatial data layers for topography, streams, and soils to reduce the potential for overestimation of habitat. Accuracy assessment was carried out using field data and high-resolution aerial photography commensurate with one of the Landsat images. The classifier can identify likely habitat for ponds larger than 0.8 ha (2 acres) with generally satisfactory results (72.1%) with a lower detection limit of approximately 0.4 ha (1 acre). Results show a 75% increase in potential larval habitats from 1999 to 2004 in the study area, primarily because of the large increase in small coalbed methane water discharge ponds. These results may facilitate mosquito abatement programs in the Powder River Basin with the potential for application throughout the state and region.

Objective: To evaluate herd-level risk factors for seropositive status of cattle to 1 or more bluetongue viruses., Animals: 110 herds of cattle in Nebraska, North Dakota, and South Dakota., Procedure: Blood samples were collected before and after the vector season. Samples were tested for antibodies against bluetongue virus by use of a commercially available competitive ELISA. Factors evaluated included descriptors of geographic location and management practices. Trapping of insect vectors was conducted to evaluate vector status on a subset of 57 operations. A multivariable logistic regression model was constructed to evaluate associations., Results: For the full data set, altitude and latitude were associated with risk of having seropositive cattle (an increase in altitude was associated with an increase in risk, and a more northerly location was associated with a decrease in risk of a premise having seropositive cattle). Import of cattle from selected states was associated with an increase in risk of having seropositive cattle. From the subset of herds with data on vector trapping, altitude and latitude were associated with risk of having seropositive cattle, similar to that for the full model. However, commingling with cattle from other herds was associated with a decrease in risk of seropositivity., Conclusions and Clinical Relevance: Findings reported here may be useful in generating additional hypotheses regarding the ecologic characteristics of bluetongue viruses and other vector-borne diseases of livestock. Sentinel surveillance programs are useful for documenting regionalization zones for diseases, which can be beneficial when securing international markets for animals and animal products.

Landscape associations of the sand fly, Lutzomyia apache, Young and Perkins, in the southwestern U.S. were investigated by light/suction trap sampling and the development of a GIS-generated distribution map. In the mid-Rio Grande River valley, N.M., female and male L. apache were captured in updraft light/suction traps set in desert shrubland, irrigation levee, and bosque vegetation communities. Small numbers of flies were captured, but the presence of males and females in spatially separate and diverse plant communities at two locations suggest that L. apache are dispersed among available vegetation types. These data, along with 22 previously published collection site records, were used with a suite of physiographic features to characterize the biogeographic conditions suitable for L. apache. Suitable conditions encompass three life zones: the Rocky Mountain steppe province, the Colorado semi-plateau province, and the American semi-desert province, all within the dry domain region of the western U.S. The potential range of L. apache was then estimated based on elevation, mean and max - min temperature, precipitation, wet days, and relative humidity. The estimated range includes large contiguous areas in north-central Colorado, east-central New Mexico and west Texas, the lower mid-Rio Grande River valley, and southern Arizona, along with smaller, patchy, areas in northern Arizona, California, Nevada, Utah, and central Idaho. The spatial relationship between the estimated distribution of L. apache and the location of livestock exposed to vesicular stomatitis virus at the onset of recent outbreaks is presented.

Historical surveillance for bluetongue virus (BTV) exposure in the United States of America (USA) has relied on periodical serological surveillance using samples collected from cattle at slaughter. Most of this surveillance has been focused on the north-eastern portion of the USA due to the lack of competent vectors of BTV in this region. For most of the states tested in this region, the prevalence of seropositive animals has been less than 2%. Recently, a study was conducted in north-central USA using sentinel cattle herds. Results of serological testing showed an increasing gradient of exposure from north to south. In addition, detection of Culicoides sonorensis showed a similar gradient with detection in the northern areas being relatively rare. The results of these studies indicate that cattle herds in the northern and north-eastern areas of the USA are likely to be free of BTV.

Environmental factors profoundly affect vectorial capacity, governing dynamics and intensity of vector-vertebrate contact in time and space (e.g. seasonal vector population densities, biting rates, and feeding frequencies). Temperature influences vector developmental rates and life history parameters, and may modify vector competence. Studies should move iteratively from field to laboratory, as attempts are made to understand complex epidemiological patterns. Simulation models can be extremely helpful in identifying and predicting geographic and seasonal trends in virus occurrence. Field and laboratory data from the Culicoides sonorensis-bluetongue virus system in North America are incorporated into preliminary estimates of virus prevalence and geographic occurrence along a latitudinal (and temperature) gradient. Geographic information systems technology is likely to be helpful in understanding vector and virus occurrence on a broader scale, especially in temperate latitudes that typify sporadic or emerging transmission zones, areas of particular concern for animal movement.

Differences in midgut microbial communities inhabiting Culicoides spp., insect vectors of virus pathogens, may affect the variation observed in the ability of these biting midges to propagate arthropod-borne viruses. As a first step toward addressing this hypothesis, midgut bacterial communities were compared between Culicoides species expected to be efficient and inefficient vectors of virus pathogens. We used 16S rDNA sequence and restriction fragment information to provisionally identify 36 bacterial genera from guts of wild adult female biting midges, Culicoides sonorensis Wirth and Jones and Culicoides variipennis (Coquillet), from two geographical locations. Bacterial identification was made by sequence analysis of 16S rDNA fragments and by terminal restriction fragment length polymorphism analysis of polymerase chain reaction-amplified 16S rDNA fragments from adult guts. Of 36 bacterial genera identified, 12 had been previously identified in other insects: Comomonas, Enterobacter, Klebsiella, Acinetobacter, Pseudomonas, Stenotrophomonas, Staphylococcus, Chryseobacterium, Moraxella, Acholeplasma, Flavobacterium, and Rickettsia, Significant differences in bacterial community composition were found between all three groups of wild adult females analyzed: live-trapped C. sonorensis, laboratory-emerged C. sonorensis, and laboratory-emerged C. variipennis.

Adult mosquitoes were collected by drop traps to compare bloodfeeding rates between cattle treated with 2 Python ear tags (10% zeta-cypermethrin and 20% piperonyl butoxide) per animal and animals that were untreated. Mosquitoes were collected both 2 and 4 wk after application of the ear tags. Bloodfeeding by Ochlerotatus dorsalis was reduced by 79 and 77%, respectively, and bloodfeeding by Ochlerotatus melanimon was reduced by 84 and 81%, respectively, at 2 and 4 wk. Based on chi-square analysis, differences in bloodfeeding rates due to treatment were significant. The effect of the treatment appeared to be repellency, because no mosquito mortality was observed at the time of collection and no mortality was observed among bloodfed mosquitoes that were collected and held for 24 h.

The possible presence of sand flies (Diptera: Psychodidae) among colonies of Gunnison's prairie dogs, Cynomys gunnisoni Baird, was investigated on or near ranches with histories of vesicular stomatitis (VS) in domestic livestock in the mid-Rio Grande River Valley, NM, and west-slope region of Colorado. Sampling was conducted at six locations, three in each region, using three methods: standard down-draft suction/light traps, up-draft suction/light traps (both supplemented with CO2), and burrow-emergence traps. Two male and four female sand flies, Lutzomyia apache, Young and Perkins were recovered from prairie dog colony and sand-sagebrush association habitats on a cattle ranch in Socorro County, NM. Sand flies were captured only in up-draft suction/light traps. This record is of interest for the following reasons: (1) sand flies have not been reported from the Rio Grande River Valley of New Mexico, (2) sand flies are biological vectors of VS viruses in other areas, (3) the mid-Rio Grande River Valley has been a focus of VS virus activity in domestic livestock during recent outbreaks, and (4) the source of vesicular stomatitis viruses that infect livestock in the western United States is unknown, but may involve introductions of virus from Mexico or an endemic cycle maintained by vector insects.

The blood feeding of mosquitoes and black flies from Hereford cattle and ponies treated with commercial formulations of permethrin was evaluated using an animal enclosure trap sample system that allowed comparison of insect blood-feeding levels between treated and nontreated animals. Blood feeding of both Aedes dorsalis Meigen and A. melanimon Dyar from heifers treated with pour-on concentrate and whole body spray treatments was reduced significantly by 79-88% at 4 d posttreatment, with apparent but not significant reductions of 61-68% at 11 d posttreatment. Simulium bivittatum Malloch and S. griseum Coquillett blood feeding was reduced significantly by 96% to >99% at 4 d posttreatment, but apparent reductions of 30-87% at 11 d posttreatment were not significant. Blood feeding of S. bivittatum from ponies treated with a permethrin fly wipe was reduced significantly by 98 and 87% at 1 and 7 d posttreatment, respectively. No evidence of treatment-induced mortality was observed for recently blood-fed female mosquitoes or black flies captured from treated animals and held for 24 h. The potential benefit of using permethrin to protect livestock from insect-transmitted pathogens was estimated with a model based on level of host attack, pathogen infection rate in the vector, and suppression of blood feeding. Suppression of blood feeding by 90% is predicted to prevent the exposure of a host to a pathogen for up tolO d at 1,000 insect feedings per d when the vector population infection rate is one insect per 1,000. If insect feedings are lower (100/d) and the insect infection rate remains at one per 1,000, protection is predicted for 100 d. In contrast, a 90% suppression of blood feeding is predicted to provide protection for less than 1 d at 1,000 feeding per day and a vector infection rate of one insect per 100.

We report sympatry among larval populations of the Culicoides variipennis complex in widespread and diverse aquatic habitats throughout the United States. Six sites in California, Nevada, New Mexico, and Texas were co-inhabited by C. v. occidentalis and C. v. sonorensis, whereas 8 sites in Florida, Georgia, Louisiana, Maryland, and Texas were co-occupied by C. v. sonorensis and C. v. variipennis. No intermediate forms were identified either electrophoretically or morphologically in adults reared from field-collected larvae and pupae. The absence of intergrades in zones of sympatry represents sufficient evidence to confirm species status for Culicoides variipennis (Coquillett) and Culicoides occidentalis Wirth & Jones, and to elevate Culicoides sonorensis to species rank (NEW STATUS). Culicoides v. albertensis Wirth & Jones is a synonym of C. sonorensis (NEW SYNONYMY); C. v. australis Wirth & Jones also is confirmed as a synonym of C. sonorensis. We also demonstrated a correlation between population taxonomic status as determined by electrophoresis and adult morphology.

Aquatic habitats with immature populations of the Culicoides variipennis (Coquillett) complex were sampled across the United States and tested for soil chemistry parameters. Indicators of organic loading, phosphate, percentage of organic matter, and nitrate were high for C. variipennis and C. sonorensis, reflecting the common occurrence of larvae in sediments contaminated with livestock waste; these factors were low in western playa lake habitats with immature C. occidentalis. Levels of salt-forming ions and indicators of salinity, notably sodium, chloride, magnesium, sulfate, boron, and conductivity, were elevated in substrates supporting all 3 species, with values that declined from very high to high across the arid west to moderate east of the Mississippi river, and differed significantly among species. Concentrations of boron differed most strongly among habitats of the respective species, ranging from exceptionally high values in playa lake substrates with C. occidentalis, to high and moderate levels in western and southeastern sites with C. sonorensis, to moderate levels for substrates in the east with C. variipennis. The presence of C. sonorensis in dairy wastewater lagoons and saline springs in geographic regions that are otherwise inhabited by C. variipennis may reflect salinity factors that regulate the distribution of the C. variipennis complex.

Entomologic and epizootic data are reviewed concerning the potential for transmission of vesicular stomatitis (VS) virus by insects, including field data from case-positive premises in New Mexico and Colorado during the 1995 outbreak of the New Jersey serotype (VSNJ). As with previous outbreaks of VSNJ in the western United States, the 1995 epizootic illustrated that risk of exposure is seasonal, increasing during warm weather and decreasing with onset of cool weather; virus activity spread from south to north along river valleys of the southwestern and Rocky Mountain states; clinical disease was detected most commonly in horses, but also occurred in cattle and 1 llama; and most infections were subclinical. Overall, 367 case-positive premises were identified during the 1995 outbreak, with foci of virus activity along the Rio Grande River south of Albuquerque, NM, in southwestern Colorado, and along the Colorado River near Grand Junction, CO. The establishment of a 16-km (10-mile) radius zone of restricted animal movement around confirmed positive premises, along with imposition of state and international embargoes, created economic hardship for livestock owners and producers. The importance of defining the role of blood-feeding insects as biological vectors of VSNJ virus relative to risk factors that promote high levels of insect transmission, such as the presence of livestock along western river valleys, blood feeding activity, and frequent transport of animals for recreational purposes, is emphasized as a basis for developing effective disease management.

Immature Culicoides variipennis (Coquillett) were sampled from aquatic habitats throughout Virginia, reared to adults, and examined by isozyme electrophoresis to assess their taxonomic status. Data from 22 counties showed that C. v. variipennis is widespread and common, the predominant taxon throughout Virginia, and genetically similar to C. v. variipennis in Maryland. Because C. v. variipennis is considered an inefficient vector of the bluetongue viruses, this observation is consistent with the low seroprevalence of bluetongue in indigenous livestock of the mid-Atlantic region. Culicoides v. sonorensis Wirth & Jones, considered to be the primary North American vector of the bluetongue viruses, was recovered in large numbers only from a wastewater lagoon at a dairy in southeastern Virginia, but also was detected at low levels in 6 other counties. Comparison of genetic distances and patterns of discriminating alleles among Virginia populations of C. v. variipennis and C. v. sonorensis showed that respective subspecies are genetically distinct and show no evidence of introgression, irrespective of geographic- and habitat-level sympatry. The persistence of a pure C. v. sonorensis population in a dairy wastewater lagoon may reflect physico-chemical factors that influence the distribution of immature C. variipennis complex populations. A better understanding of the distribution of the C. variipennis complex will benefit regionalization of U.S. exports of livestock and livestock germplasm to bluetongue-free countries.

The spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Benner is transmitted by Ixodes scapularis Say, a vector of Lyme disease. As a 1st step into investigating the possibility of biocontrol of the tick, we identified the microbiota associated with the ticks. We collected, identified, and determined the sex of ticks from foliage and deer. Seventy-three initial bacterial isolates were recovered from 43 ticks (27 adults and 16 nymphs). The bacteria isolated from nymphs were qualitatively different (mainly gram-negative cocci) from the bacteria isolated from adult ticks (gram-negative and gram-positive rods). To determine long-term viability, these isolates were stored for 6 mo under laboratory conditions. After storage, 63 surviving bacterial isolates were characterized using the Biology System of identification by substrate utilization. Forty-four isolates were identified to the species level. Our characterization efforts focused on the 40 spore-forming bacteria, which could prove useful in the biocontrol of ticks. Eleven species of Bacillus were identified. Bacillus thuringiensis-B. cereus was the predominant species group isolated. Six isolates from this group formed crystals.

As a measure of the risk for exposure to Lyme disease, we estimated the distribution of host-seeking adults of the blacklegged tick, Ixodes scapularis Say, on dairy farms in Barron County in northwestern Wisconsin. Vegetation ecotypes that were common to 18 farms that were representative of the county were surveyed by flag sampling. Tick prevalence and abundance, which were similar during fall and spring periods, were very low in farmhouse yards and forage croplands; only a single male was collected from 17 lawns. Sampling of 18 pastures with lactating cows also yielded only a single I. scapularis. In contrast, I. scapularis adults were captured in 9 of 37 samples from 18 pastures with heifers and dry cows; in those pastures, ticks were associated with woods and secondary vegetation or margins of pastures adjacent to woodlands. Blacklegged ticks were most prevalent and numerous in ungrazed woodlands; adults were captured in 27 of 53 samples on 13 of 15 farms, particularly when evidence of white-tailed deer, Odocoileus virginianus (Zimmermann), was apparent. The risk of encountering adult blacklegged ticks on dairy farms in Barron County, Wisconsin is therefore greatest in woodlands habitat. The presence of adult ticks in pastures with heifers and dry cows establishes an ecological basis for the exposure of dairy cattle to adult I. scapularis. Pastures with lactating cows, farmhouse yards, and forage croplands represent negligible risk.

The attachment site pattern of adult Ixodes scapularis Say on white-tailed deer and horses in Maryland was determined by whole-body examinations during fall and spring periods of tick host-seeking activity. On deer in the fall, both female and male I. scapularis attached largely to anterior dorsal body regions, with attachment to the ears (outside), head, neck, and brisket accounting for 87.9% of females and 86.6% of males. The attachment pattern of females differed between bucks and does during fall, but not in spring, and both females and males were more abundant on bucks than does during fall, but not in spring. Neither female nor male attachment patterns on deer differed between fall and spring seasons. In contrast to deer, the ears and neck of horses were largely devoid of blacklegged ticks, and 84% of the females were attached either on the chest, in the axillae of the fore and rear legs, or under the jawbone. The restricted attachment of female blacklegged ticks to ventral body regions of horses may reflect avoidance of light. An understanding of the attachment patterns of adult I. scapularis, an increasingly abundant and economically important species, enhances sampling of feeding ticks, deticking to limit host irritation or exposure to tick-borne pathogens, and identifies body areas that should be targeted for delivery of repellents or acaricides.

Adult blacklegged ticks, Ixodes scapularis Say, were confined to clay islands each surmounted with a vertical glass rod, and tick activities were videotaped continuously for 48 h. Some rods were treated basally or apically with substances rubbed from pelage associated with the tarsal or interdigital glands of white-tailed deer, Odocoileus virginianus (Zimmermann). Except for the activity immediately following their release, tick activity on both days was greatest during the period from 1700 to 2300 hours, which coincided with the onset of scotophase. Ticks were most active when rods had interdigital gland substances applied to their basal 2 cm, whereas they were least active when confined with rods treated with tarsal gland substances on their apical 2 cm. Overall, ticks spent more time on the apical 2 cm of the glass rods during the scotophase than during the photophase. The highest level of apical arrestment among treated and untreated rods occurred when the rod tips were treated with tarsal gland substances, with female ticks on the apical 2 cm of the rods 70-100% of every 3-h period beginning with the period from 2000 to 2300 hours on day 1. In contrast, when tarsal gland substances were applied to the basal 2 cm of the rods, the ticks spent < 40% of every period on day 2 on the rod tips.

Silt fence barriers were set along pasture fencelines and evaluated as a method of restricting the dispersal of blacklegged tick, Ixodes scapularis Say, adults and nymphs from woodlands into adjacent horse pastures. The barriers received no acaricidal treatment for the 1st cohort of adults. Thereafter the woods side of the barriers was sprayed with cyfluthrin at the onset of each season of host seeking activity of nymphs and adults. When high densities of adults were present, the barriers significantly limited the numbers of ticks in pastures. Nymphs, however, were not significantly fewer in numbers in pasture areas associated with the barriers compared with control areas. Marked adult ticks released in woodlands and ecotones were recaptured on mowed verges and pastures, but there was little dispersal from the woods edge into the woods.

Marked nymphal and adult blacklegged ticks, Ixodes scapularis Say, were released in 4 host-exclusion cages and 4 similar control areas, all straddling the woods-pasture interface. Both nymphs and adults were recaptured by flagging at regular intervals outside the cages, having therefore actively dispersed > 4.5 m (i.e., without involvement of vertebrates). Nymphs were recaptured much more often ( > 90%) in the woods than pastures, whereas 62.8% of recaptured adults were taken in pastures. Females were recaptured in equal numbers in pastures and woods, but 75.4% of recaptured males were in pastures. Adults that dispersed into pastures were recaptured an average of 1.6 and 3.7 m from the woods edge in 1992 and 1993, respectively, and as far as 7-8 m from the woods edge. Nymphs dispersed shorter distances than adults with 66% of the recaptured nymphs found 2-3 m from their release points, and > 46% of recaptured adults found > 5 m from their release points. Twice as many nymphs were recaptured from the caged than uncaged sites. The lower numbers of nymphs recaptured from control sites compared with caged sites are probably the result of host acquisition; the absence of this discrepancy with the adults may reflect by their ability to move relatively quickly from the host-exclusion cages and become available for host contact.

In a field test, adult blacklegged ticks, Ixodes scapularis Say, of both sexes exhibited an arrestant response to substances associated with external glands on the legs of white-tailed deer, Odocoileus virginianus (Zimmermann), their principal host. Substances rubbed from the pelage covering tarsal and interdigital glands were applied to artificial vantage points simulating vegetation on which I. scapularis adults wait for host contact. A combination of tarsal substances (applied to the apex of the simulated vantage point) and interdigital gland substances (applied to the horizontal base) elicited a greater response than either treatment alone. A minimal response was observed on untreated vantage points. In laboratory bioassays using glass tubing as vantage points, substances associated with preorbital glands of deer elicited a strong arrestant response among I. scapularis females, whereas samples rubbed from the forehead, back, and a nonglandular area on deer tarsi evoked weak arrestant responses. These results support the hypothesis that the kairomonal properties of host-generated residues, either in conjunction with or in lieu of the effects of carbon dioxide, help account for the prevalence of host-seeking ticks along animal trails.

In a series of 4 trials, dairy calves housed in outdoor hutches were administered technical cyromazine daily at rates of 0, 0.1, 0.5, and 1.0 mg/kg body weight. Cyromazine was excreted primarily in the urine. The 2 highest rates prevented the development of immature stages of both the house fly, Musca domestica L., and the stable fly, Stomoxys calcitrans (L.). Analysis of calf body tissues for cyromazine and its metabolite, melamine, indicated that highest combined residues ( < or = 0.35 ppm) were found in the kidney. Lower levels of residues were found in kidney fat and liver, and occasionally in round muscle.

Unfed adult blacklegged ticks Ixodes scapularis Say, were tested under laboratory conditions for behavioral responses to substances rubbed from external glands on legs of white-tailed deer, Odocoileus virginianus (Zimmermann). In replicated trials, significantly more female ticks became stationary on portions of vertical glass tubing rubbed with the tarsal gland substances of both bucks and does than on nontreated tubing. This behavior, apparently an arrestant response, was infrequent among males. White-tailed deer urinate upon their tarsal glands, and doe urine also produced an arrestant response among female ticks. Metatarsal gland secretions of bucks elicited no arrestant response in either male or female I. scapularis, but doe metatarsal gland secretions elicited low-level positive responses from both sexes. A low-level arrestant response also was exhibited by females to secretions from the interdigital glands of bucks. In a second bioassay, three times as many females came to rest on the terminal ends of vertical glass rods whose bases were treated with secretions from buck interdigital glands than on rods with nontreated bases. This suggests that interdigital gland secretion influences blacklegged tick climbing behavior. Substances produced by or associated with the leg glands of O. virginianus may therefore serve as kairomones for host-seeking adult I. scapularis; interdigital gland secretions on soil or leaf litter may signal active deer trails, and tarsal gland substances may denote portions of vegetation contacted previously by white-tailed deer. In nature, use of these chemical cues by host-seeking adult I. scapularis may increase the probability of acquiring a suitable host.

To clarify the risk of pastured livestock for exposure to Ixodes scapularis Say (Acari: Ixodidae), we estimated the host-seeking activity of nymph and adult blacklegged ticks at the woods-pasture interface on horse farms in Maryland. Parallel linear transects of 100 m length and 1 m width were sampled repeatedly in pastures and adjacent woodland locations during periods of nymph (early summer) and adult (fall and spring) host-seeking activity. Data collected over two successive years indicated that adults were most abundant in ecotonal vegetation at the wood's edge, median values of 6.4 and 2.2 ticks per 100 m2 sample during fall and 1.2 and 0.5 ticks per 100 m2 sample for spring periods. Nymphs were most abundant in the shallow woods location, median values of 4.2 and 35 ticks per 100 m2 sample, followed by the deep woods and wood's edge locations. Host-seeking nymph and adult black-legged ticks also were collected repeatedly in pasture vegetation, median values ranging from 0.2-0.8 ticks per 100 m2 sample, with a progressive decrease in abundance from the fenceline into pasture. Adults and nymphs both were uncommon more than 5 m into pastures, where only two adults and one nymph were captured in 84 (fall and spring) and 24 (summer) 100-m2 samples, respectively. Levels of adult and nymph host-seeking in pasture vegetation were spatially correlated with tick abundance in adjacent woodlands when ticks were numerous; this condition presumably reflects a spillover of ticks from the woodlands-based population. These findings expand knowledge of black-legged tick host-seeking behavior and establish a basis for the exposure of pastured livestock to nymphs and adults.

Six preparations of egg yolk media inoculated with Escherichia coli (Migula) were evaluated as an in vitro growth system for immature house flies, Musca domestica L. Larval development, based on pupation and eclosion success, was normal on all media supplemented with E. coli, but few larvae survived without bacteria (4%). Pupation (72%) and eclosion (63%) were significantly higher on egg yolk media without mannitol than on media with mannitol or on blood agar controls.

We describe a version of the standard tick drag-flag modified for use in close-growing and tangled vegetation, as well as under ornamental shrubbery and fallen branches. Two major features of the sweep are: (1) it allows the user to remain upright with the flag parallel to the ground, thus sampling effectively beneath low and fallen branches and around shrubs, as well as capturing host-seeking ticks in advance of the operator; and (2) the use of a flannel rubberized-laminate fabric (crib sheet) for the flag that is snag-proof and highly durable in dense and thorny vegetation. In simultaneous 100-m samples, the sweep was as effective as the 1-m standard tick drag for capturing nymphs of the deer tick, Ixodes dammini Spielman, Clifford, Piesman & Corwin, where understory vegetation was sparse, but was twice as effective in dense vegetation, capturing significantly more I. dammini nymphs. The sweep also captured nymphs of the American dog tick, Dermacentor variabilis (Say); rabbit tick, Haemaphysalis leporispalustris (Packard); and lone star tick, Amblyomma americanum (L.).

To investigate the relationship between immature (maggot) house flies, Musca domestica, and bacteria, we compared the development of sterile first-instar maggots in each of 10 pure blood agar cultures of bacteria with growth on sterile blood agar (negative control) and on standard house fly rearing medium (positive control). Nine species of bacteria representing gram-negative and gram-positive rods, coccoid, and micrococcoid cell types supported house fly growth on blood agar. One bacterium, a strain of Bacillus cereus, inhibited maggot growth. The percent pupation for maggots that developed in the presence of eight of nine bacteria (range, 41-69%), was significantly greater than in sterile blood agar (0-5%), and did not differ significantly from maggot growth in the rearing medium (50-90%). Average pupal weight for maggots that developed on blood agar with bacteria ranged from 19 to 21 mg, a reflection of favorable growth conditions. Average pupal weight in the presence of three bacteria (19.9, 19.4, and 19.4 mg) was significantly less than respective pupal weights in house fly rearing medium (24.0, 22.3, and 22.1 mg), but there was no difference in average pupal weight with six bacteria and the house fly rearing medium. These findings illustrate that bacteria or their metabolic products are essential as nutrients for house fly maggot growth in blood agar; a wide variety of adventitious bacteria can contribute to the suitability of an organic substrate for maggot growth; and a naturally occurring isolate of B. cereus limits house fly maggot growth in blood agar, a relationship that has not been reported previously.

The identification of apparently fastidious microorganisms is often problematic. DNA from a rickettsia-like agent (called the ELB agent) present in cat fleas could be amplified by PCR with conserved primers derived from rickettsial 17-kDa common protein antigen and citrate synthase genes but not spotted fever group 190-kDa antigen gene. Alu I sites in both the 17-kDa and citrate synthase PCR products obtained with the rickettsia-like agent and Rickettsia typhi were different even though both agents reacted with monoclonal antibodies previously thought specific for R. typhi. The DNA sequence of a portion of the 17-kDa PCR product of the rickettsia-like agent differed significantly from all known rickettsial sequences and resembled the 17-kDa sequences of typhus more than spotted fever group rickettsiae. The rare stable transovarial maintenance of this rickettsia in cat fleas has important implications for the disease potential of cat fleas.

Sand, gravel, sawdust, and pine shavings were used as bedding in outdoor calf hutches and compared with straw relative to the density of immature (maggot) house flies, Musca domestica, and stable flies, Stomoxys calcitrans. In 6-wk field trials, average densities of house and stable fly maggots in concrete mix sand ranged from only .3 to 1.6 and 0 to .1 maggots/L, respectively; pea size gravel bedding also strongly suppressed densities from less than .1 to .3 and less than .1 to .1 maggots/L, respectively. These densities represent reductions of 76 to greater than 99% relative to straw bedding, but both sand and gravel compacted and became soiled with calf feces, which resulted in unacceptable bedding sanitation and foul odors. Densities of house and stable fly maggots in pine shavings did not differ from those in straw bedding. Nevertheless, in sawdust bedding, maggot density was limited to averages of 1.4 to 8.3 house and 9.8 to 11.8 stable fly maggots/L; this represented reductions of 45 to 91% relative to straw. In a follow-up trial, house and stable fly maggot densities in sawdust averaged 11.3 and 43.9 maggots/L, respectively, reductions of 77 and 46%. These findings suggest that bedding calf hutches with sawdust during warm weather can be useful as an ecologically sound approach to controlling muscoid fly populations on dairy farms.

We report the ultrastructure of a rickettsia-like microorganism in a colonized population of the cat flea Ctenocephalides felis (Bouché). The microorganism occurs principally in the cytoplasm of midgut cells, but similar microorganisms were detected in the tracheal matrix, muscle, hypodermis, ovaries, and the epithelial sheath of the testes. The microorganism has a well-defined cell membrane consistent with rickettsia and measures 0.25-0.45 microns in diameter with lengths up to 1.5 microns. It was observed repeatedly in fleas of 1 laboratory colony, including newly emerged non-bloodfed specimens, but not in specimens from several other sources.

The capability of field-collected American dog ticks, Dermacentor variabilis, to infect horses with Ehrlichia risticii, causative agent of Potomac horse fever (PHF), was examined by allowing adult ticks collected from horse farms with a history of PHF to feed on susceptible horses. More than 500 male and female ticks attached and fed on 3 test horses; however, no clinical or serologic evidence of PHF was observed in treated or control horses. All horses were challenge exposed with E risticii-infective blood by inoculation at 60 to 65 days after ticks fed, and all developed clinical PHF with subsequent seroconversion. The data, therefore, indicated that adult D variabilis, a common parasite of horses on Maryland premises where PHF is enzootic, may not serve as a vector of E risticii.

A serological study of antibodies to Ehrlichia risticii was carried out on 10 species of wild and domestic mammals found on or near 21 horse farms in an area of the USA in which Potomac horse fever is endemic. No antibodies were found in 133 peridomestic rodents (Norway rats and house mice), nor in 108 wild rodents (white-footed mice and meadow voles) captured on farms. Three of the six domestic animal species examined, cats, pigs and a goat, showed serological evidence of exposure to E risticii. Seropositive animals were detected on three of the 21 premises. The eight seropositive cats (of 48 cats tested) were on two farms, and the three seropositive pigs (of 14 tested) were all on one farm which lay some 3 km from where the one seropositive goat (of three tested) was found. None of the 79 dogs, 75 cattle and seven sheep tested had antibodies to E risticii. The significance of these findings is discussed in the light of current understanding of the transmission of Potomac horse fever and of the epidemiology of other related ehrlichial diseases.

Studies of interactions between face flies and Holstein cattle show that the frequency and duration of aggregation episodes can be associated with exposure to face flies and that the numbers of flies on cows during aggregation is inversely correlated with cow nearest-neighbor distance, a relationship that remains relatively consistent within herds. Furthermore, aggregation in herds exposed to face flies neither altered herd grazing time nor grazing patterns, which indicates that aggregation behavior is expressed during nongrazing, idling periods. Initial observations show that cow aggregation in small herds does not compromise animal thermoregulation.

One hundred ten white-footed mice (Peromyscus leucopus) were captured on horse farms in south-central Maryland, examined for ticks, and tested for specific antibodies to Ehrlichia risticii, the causative agent of Potomac horse fever. Peromyscus leucopus were consistently infested with immature American dog ticks (Dermacentor variabilis), with monthly prevalences as high as 80%. Sera from all 97 P. leucopus tested for antibodies to E. risticii were negative. This indicates that P. leucopus is not a reservoir of E. risticii, and suggests that immature D. variabilis do not acquire E. risticii in feeding upon white-footed mice.

Experimental bedding materials and a novel delivery method of cyromazine (Larvadex) were evaluated as replicated treatments in outdoor calf hutches for effect on the density of immature Musca domestica L. and Stomoxys calcitrans (L.). In 6-wk trials, overall density of Musca domestica L. and Stomoxys calcitrans (L.) in straw bedding averaged 36.2 and 52.6 maggots/liter, respectively, compared with respective average densities of 9.0 and 16.2 for wood chips and 10.4 and 20.0 for wood chips over a hydraulic fabric filter system. These values represent average reductions of 80 and 69% and 77 and 68%, respectively. Densities of M. domestica and S. calcitrans in ground corncob over the filter system averaged 13.3 and 4.1 maggots/liter in 3.2-mm size corncob particles, and 1.7 and 1.2 for 6.4-mm size corncob particles (average reductions of 62 and 87% and 90 and 96%, respectively) relative to straw bedding. Densities of these two species in sand bedding averaged 2.8 and 0.4 maggots/liter (average reductions of 93 and 99%), but sand became compacted and soiled with calf urine and feces after several weeks. Cyromazine excreted in calf urine limited density of both species in straw to an average of 11.0 and 15.6 maggots/liter, respectively (a 58 and 79% suppression relative to untreated straw). These data confirm that straw bedding promotes muscoid maggot growth and illustrate that alternative calf hutch bedding systems and urine delivery of cyromazine may improve muscoid fly management on dairy farms by limiting the development of muscoid maggots.

To investigate interrelations among factors potentially affecting body temperature, we observed body temperature, activity, and relative aggregation of 3 to 5 dry cows from a herd of 12 to 15 every 20 min. Ambient conditions were noted every 1 h and fly counts every 3 h. Observations during daylight for 5 d with and without shade indicated effects of shade were minimal and were extended to 24 h without shade at six weekly intervals. Cows lie down during the evening, grazed near sunrise and sunset, and alternated standing and grazing during the day. The aggregation index was greatest during periods of standing and least during grazing; however, it remained constant across periods of similar activity. Cows shifted activity from grazing to standing during periods of increased fly activity. Ambient temperatures ranging from 13 to 35 degrees C had little influence on measured variables. Body temperatures showed one to three daily dips (greater than 1 degree C) and a hysteresis pattern. Almost all dips were associated with transitions from lying to grazing. Body temperature was constant in the morning, rose to a higher level in the afternoon, and remained high until the next morning.