Relationship Between Weather and Changes in Annual and Seasonal Abundance of Culicoides sonorensis (Diptera: Ceratopogonidae) in Alberta

Factors influencing annual and seasonal abundance of Culicoides sonorensis (Wirth and Jones) (Diptera; Ceratopogonidae) were examined at 10 sites in southern Alberta using negative binomial regression. Annual abundance varied among locations with greatest abundance in a narrow geographic band between -112.17 and -112.64°W longitude and 49.32 and 50.17°N latitude. Sites were grouped depending on whether abundance was continuous and high; discontinuous and low; or sporadic and low without much loss of information. Maximum annual abundance declined with spring precipitation, increased with spring temperature, and was unrelated to spring relative humidity, suggesting that abundance is highest during years with early drought conditions. Seasonal abundance was associated with the same factors but was further influenced by temperature and relative humidity during the sample intervals. Lagged effects were apparent, suggesting abundance increased with warmer temperatures over a six-week period, and increased when relative humidity declined closer to the sampling period. Predicted values were slightly biased and tended to overestimate observed data, but this could be adjusted using calibration curves. The model can also be used to predict presence/absence of C. sonorensis and will be useful for developing risk assessments.

A knowledge, attitudes, and practices study on ticks and tick-borne diseases in cattle among farmers in a selected area of eastern Bhutan

Livestock farming plays an important role in supporting the livelihood of resource-poor subsistence farmers in Bhutan. However, ticks and tick-borne diseases (TBDs) are one of the major constraints to livestock farming due to their negative effect on health and production. To date, no study has been conducted in Bhutan to assess farmers' knowledge, attitude, and practices (KAP) about ticks and TBDs in cattle, although such information is essential in ensuring the development and adoption of effective prevention and control measures. Therefore, a KAP survey was conducted among 246 cattle owners in the Samkhar sub-district of eastern Bhutan in June 2019, using a structured questionnaire. Based on our scoring criteria, 52% [95%CI: 45.5-58.4] had adequate knowledge about ticks as potential vectors of diseases. Logistic regression analysis showed that the individuals who practiced a stall-feeding system of cattle rearing were 2.8 times [OR = 2.8 (95%CI: 1.66-4.78)] more likely to have adequate knowledge than others. Sixty-eight percent [95%CI: 62.5-74.4] had a favorable attitude toward tick prevention and control programs. Men were 1.95 times [OR = 1.95 (95%CI: 1.09-3.55)] more likely to have a favorable attitude than women, and the individuals who practiced a stall-feeding system were 2.59 times [OR = 2.59 95%CI: 1.45-4.78)] more likely to have a favorable attitude than others, after adjusting for the effect of other variables in the model. Overall, only 38% [95%CI 32.5-45] of the respondents reported tick infestation as one of the most important animal health problems, but 100% reported using acaricides to control ticks in cattle. Despite a high level of acaricide usage, the level of knowledge was low among the farmers interviewed. Findings from this study underline the importance of considering identified knowledge gaps and initiating education efforts to improve the adoption of effective tick prevention and control measures among farmers.

Identification, Distribution, and Habitat Suitability Models of Ixodid Tick Species in Cattle in Eastern Bhutan

Tick infestation is the most reported parasitological problem in cattle in Bhutan. In May and June 2019, we collected ticks from 240 cattle in two districts of Eastern Bhutan. Tick presence, diversity, and infestation prevalence were examined by morphological identification of 3600 live adult ticks. The relationships between cattle, geographic factors, and infestation prevalence were assessed using logistic regression analyses. Habitat suitability for the tick species identified was determined using MaxEnt. Four genera and six species of ticks were found. These were Rhipicephalus microplus (Canestrini) (70.2% (95% confidence interval (CI): 68.7-71.7)), Rhipicephalus haemaphysaloides Supino (18.8% (95% CI: 17.5-20.1)), Haemaphysalis bispinosa Neumann (8.2% (95% CI: 7.3-9.1)), Haemaphysalis spinigera Neumann (2.5% (95% CI: 2-3)), Amblyomma testudinarium Koch (0.19% (95% CI: 0.07-0.4)), and a single unidentified Ixodes sp. Logistic regression indicated that the variables associated with infestation were: longitude and cattle age for R. microplus; latitude for R. haemaphysaloides; and altitude and cattle breed for H. bispinosa and H. spinigera. MaxEnt models showed land cover to be an important predictor for the occurrence of all tick species examined. These findings provide information that can be used to initiate and plan enhanced tick surveillance and subsequent prevention and control programs for ticks and tick-borne diseases in cattle in Bhutan.

Comparison of Habitat Suitability Models for Haemaphysalis longicornis Neumann in North America to Determine Its Potential Geographic Range

Haemaphysalis longicornis Neumann, 1901 is a vector of many pathogens of public and veterinary health importance in its native range in East Asia and introduced range in Oceania. In North America, this tick was first detected in New Jersey in 2017. Currently, this tick has been reported from 15 states of the United States. In this study, we modeled the habitat suitability of H. longicornis using the MaxEnt modeling approach. We separated occurrence records from the published literature from four different geographical regions in the world and developed MaxEnt models using relevant environmental variables to describe the potential habitat suitability of this tick in North America. The predictive accuracy of the models was assessed using the U.S. county locations where this tick species has been reported. Our best model predicted that the most suitable North American areas for geographic expansion of H. longicornis are from Arkansas–South Carolina to the south of Quebec–Nova Scotia in the east, and from California to the coast of British Columbia in the west. Enhanced surveillance and further investigation are required to gain a better understanding of the role that this tick might play in the transmission of diseases to humans and animals in North America.

Sampling Considerations for Adult and Immature Culicoides (Diptera: Ceratopogonidae)

Developing sampling programs for Culicoides can be challenging due to variation in ecology and behavior of the numerous species as well as their broad distributions and habitats. In this paper, we emphasize the need to clearly define research goals to select appropriate sampling methods. This includes not just the choice of sampling device, but also choice of attractant, site, number of traps per site, the duration and frequency of sampling, and the number of traps per unit area. Animal-baited trapping using enclosure traps and direct animal aspiration is more labor-intensive but yields information on species attracted to specific hosts as well as their biting rates. Sampling immatures is discussed with respect to choosing collection sites in semiaquatic mud, soil, and rich organic habitats. Sorting and extracting larvae using emergence traps, flotation, and Berlese funnels is also discussed.

Evaluating the Addition of CO2 to Black Light Traps for Sampling Culicoides (Diptera: Ceratopogonidae) in Alberta

We examined the effect of augmenting black light trap with CO2 at two release rates for monitoring and surveillance of Culicoides at northern latitudes. Species composition was highly correlated among black light (BL) traps with no CO2 (BL0 traps) and traps augmented with 300 and 1000 ml/min CO2 (BL300 and BL1000 traps, respectively); however, traps augmented with CO2 captured one to three more rare species than BL0 traps and can detect rare species that might be missed if BL0 traps were used. Addition of CO2 increased the number of individuals captured from 1.4 to 38.5-fold for BL300 traps and from 1.5 to 153.5-fold for BL1000 traps. This advantage may be lost in areas with low abundance as might be expected at the limits of species. The daily probability of detecting a species was greater for traps augmented with CO2, but this can be compensated for by operating BL0 traps for sufficient time. The association between numbers captured by BL0 and BL300 and BL1000 traps also suggests that BL0 traps may provide useful measures of relative abundance for Culicoides sonorensis, Culicoides davisi, and Culicoides riethi, again providing the BL0 traps are left to operate for some period. Measurements of diel activity were influenced by trap type only for a single species and were primarily determined by solar radiation, temperature, and windspeed. Overall, the use of BL0 only traps for widescale surveys is supported, especially given their convenience.

Can Subclinical Infestation by Paralyzing Dermacentor andersoni (Acari: Ixodidae) Induce Immunity to Tick Paralysis in Sheep?

Cattle and sheep can develop immunity to paralysis caused by Dermacentor andersoni Stiles; however, this has been reported only in animals that were initially challenged with a high dose of ticks and exhibited clear symptoms of paralysis. Paralysis in sheep occurs in a dose-dependent fashion, with no paralysis occurring in sheep exposed to <0.2 ticks per kilogram sheep weight, and 100% paralysis in sheep exposed to >0.8 ticks per kilogram. This experiment was conducted to determine if sheep exposed to a low dose of ticks would also develop immunity to paralysis. Sheep were exposed to either a low (0.2 ticks per kilogram) or high dose of ticks (0.8 ticks per kilogram), then re-exposed to a second challenge of a paralyzing dose of ticks. All naïve sheep (eight of the eight) were paralyzed, while paralysis occurred in only four of the eight sheep previously exposed to a low dose, and one of the eight sheep previously exposed to a high dose. Results indicate that immunity can develop when sheep are exposed to a subclinical dose of paralyzing ticks, but in a smaller percentage of animals than those exposed to a high dose of ticks. Vaccine development perhaps remains the best option for nonacaricidal control of tick paralysis.

Embryo Development and Morphology of the Rocky Mountain Wood Tick (Acari: Ixodidae)

Dermacentor andersoni Stiles embryogenesis was observed using fluorescent and scanning electron microscopy for eggs held under laboratory conditions (25°C and at 93% relative humidity). Early embryonic cell divisions appeared to be synchronous and holoblastic, giving rise to a uniform blastoderm surrounding the yolk. The cells of the blastoderm became concentrated on one side of the embryo, forming the segmented germ band. Distinct opisthosomal and prosomal segment morphologies, which are characteristic of chelicerate embryos, were observed during germ band elongation. Mouth and leg appendages grew from the prosomal segments. As development progressed, the segments were fused into the idiosoma and capitulum of the free-living larval form. An embryo staging system was established based on embryo developmental morphology and the timing of morphogenetic events. The staging system will serve as a basis for future studies directed at understanding morphogenetic mechanisms or for observing the impact of abiotic factors, such as temperature or humidity, on tick development.

Influence of temperature on oviposition by Dermacentor andersoni (Acari: Ixodidae)

The effects of temperature on oviposition by Dermacentor andersoni (Stiles) was examined using replete females ranging in weight from 30 to 1,198 mg. Survivorship was >96% during the preoviposition periods and declined during oviposition period. Egg production peaked earlier and at greater levels as temperature increased. Longevity, preoviposition period, and oviposition period declined as temperature increased. Replete weight had minor effects on measures of time, but smaller females tended to have greater longevity and preoviposition periods, and shorter oviposition periods. Temperature and replete weight both had large effects on measures of oviposition success such as the amount of eggs laid, the conversion efficiency index, and daily egg production. Lower temperatures and replete weight resulted in greater oviposition failure, and reduced egg production and conversion efficiency. Oviposition was greatly inhibited at 10 degrees C, suggesting this is near the lower temperature limit for development. However, egg production was reduced at temperatures < 20 degrees C, suggesting that the northern edge of the distribution may be influenced by the effects of temperature on oviposition.

Distribution of Culicoides sonorensis (Diptera: Ceratopogonidae) in Alberta, Canada

The distribution of Culicoides sonorensis Wirth and Jones was examined in Alberta, Canada. Sampling was conducted weekly using blacklight traps at eight locations in 2009, and 10 locations during 2010-2012. Nine supplemental sites were sampled twice annually during both 2011 and 2012. Abundance of C. sonorensis was consistently greatest at a site near the U.S. border, and declined in a northerly direction. Mean annual abundance at this site ranged from 6.4- to > 1,000-fold greater across positive sites. Data from a less extensive survey conducted during 2002-2006 were included in the remaining analyses. C. sonorensis was distributed below a diagonal spanning 49 degrees 30' N, 113 degrees 0' W to 51 degrees 21' N, 110 degrees 40' W. The relationship between the proportion of weekly samples positive and mean annual abundance at a site was determined and indicated that the proportion of positive samples could be used as a surrogate measure of abundance to overcome issues associated with the extreme variation in abundance. A series of logistic regression models were developed and evaluated to determine the effects of spatial (latitude and longitude), climatic (historic temperature and precipitation during the warmest quarter), and weather (temperature during the sample interval and spring precipitation) on abundance as measured by the proportion of positive samples. Spatial and climatic variables set the overall level of abundance, while weather variables added seasonal fluctuations within years, and also fluctuations between years. These data will be useful for long-term monitoring of C. sonorensis and as a baseline for detecting shifts in abundance that might occur because of climate change.

Movement of male Dermacentor andersoni (Acari: Ixodidae) among cattle

Movement of male Dermacentor andersoni (Stiles) was examined among 54 pairs of artificially infested donor and recipient cattle during a 3-yr period. The number of males declined at a rate independent of the initial level of infestation, while the rate of decline of females on the donor animals tended to increase with initial infestation level. Male tick movement to recipient cattle was observed in 26 of 54 (48%) of the animal pairs, but varied among years and trials. Movement tended to be greater during April compared with May and June. The daily probability of movement averaged (SD) 0.067 (0.082), and the number of males moving per day averaged (SD) 0.083 (0.228). Logistic and Poisson regression models were developed and indicated that movement was determined by interactions between the number of males on the donor animals, differences in the number of females on the donor and recipient cattle, temperature, and female age. These models can be used to incorporate movement into tick population models.

Mortality of adult Stomoxys calcitrans fed isolates of Bacillus thuringiensis

We examined the ability of five isolates of Bacillus thuringiensis Berliner to cause mortality in adult stable flies, Stomoxys calcitrans (L.). Isolates Bacillus thuringiensis tolworthi 4L3 (serotype 9), Bacillus thuringiensis darmstadiensis 4M1 (serotype 10a10b), Bacillus thuringiensis thompsoni 401 (serotype 12), Bacillus thuringiensis thuringiensis HD2 (serotype 1), and Bacillus thuringiensis kurstaki HD945 (serotype 3a3b3c) were administered to adult flies in diets containing blood only, sugar only, and both sugar and blood combined. B. t. tolworthi 4L3 had no effect on adult mortality regardless of the feeding substrate. The remaining isolates tended to cause the greatest mortality when administered in blood alone. B. t. thompsoni 401 was the only isolate that consistently caused adult mortality when fed in blood at concentrations ranging from 0.21 to 50.0 microg of protein per ml of blood. This isolate also caused mortality when applied topically. The time to 50% mortality declined with dose and reached a lower asymptote at approximately equal to 1.3 d at an oral dose of 8.75 microg/ml and at a topical dose of 0.14 microg per fly.

Effects of temperature on mortality of larval stable fly (Diptera: Muscidae) caused by five isolates of Bacillus thuringiensis

We examined the effects of temperature on mortality of larval stable fly [Stomoxys calcitrans (L.)] caused by Bacillus thuringiensis tolworthi 4L3, B. t. darmastedensis 4M1, B. t. thompsoni 401, B. t. thuringiensis HD2, and B. t. kurstaki HD945. At moderate doses, mortality caused by all isolates ranged from 87 to 99% at 15 degrees C and declined to 29-63% as temperature increased to 30 degrees C. A similar pattern was seen when a higher dose was used, except that the reduction in mortality at warmer temperatures was not as great as was seen with the moderate doses. Insecticidal activity of each isolate against first-instar larvae was reduced by only 5-15% after 5 d in the medium. Mortality of second- and third-instar larvae ranged from 2 to 21%, suggesting the isolates were less effective against larger larvae.

Arthropod Surveillance Programs: Basic Components, Strategies, and Analysis

Effective entomological surveillance planning stresses a careful consideration of methodology, trapping technologies, and analysis techniques. Herein, the basic principles and technological components of arthropod surveillance plans are described, as promoted in the symposium "Advancements in arthropod monitoring technology, techniques, and analysis" presented at the 58th annual meeting of the Entomological Society of America in San Diego, CA. Interdisciplinary examples of arthropod monitoring for urban, medical, and veterinary applications are reviewed. Arthropod surveillance consists of the three components: 1) sampling method, 2) trap technology, and 3) analysis technique. A sampling method consists of selecting the best device or collection technique for a specific location and sampling at the proper spatial distribution, optimal duration, and frequency to achieve the surveillance objective. Optimized sampling methods are discussed for several mosquito species (Diptera: Culicidae) and ticks (Acari: Ixodidae). The advantages and limitations of novel terrestrial and aerial insect traps, artificial pheromones and kairomones are presented for the capture of red flour beetle (Coleoptera: Tenebrionidae), small hive beetle (Coleoptera: Nitidulidae), bed bugs (Hemiptera: Cimicidae), and Culicoides (Diptera: Ceratopogonidae) respectively. After sampling, extrapolating real world population numbers from trap capture data are possible with the appropriate analysis techniques. Examples of this extrapolation and action thresholds are given for termites (Isoptera: Rhinotermitidae) and red flour beetles.

Dispersion and sampling of adult Dermacentor andersoni in rangeland in Western North America

A fixed precision sampling plan was developed for off-host populations of adult Rocky Mountain wood tick, Dermacentor andersoni (Stiles) based on data collected by dragging at 13 locations in Alberta, Canada; Washington; and Oregon. In total, 222 site-date combinations were sampled. Each site-date combination was considered a sample, and each sample ranged in size from 86 to 250 10 m2 quadrats. Analysis of simulated quadrats ranging in size from 10 to 50 m2 indicated that the most precise sample unit was the 10 m2 quadrat. Samples taken when abundance < 0.04 ticks per 10 m2 were more likely to not depart significantly from statistical randomness than samples taken when abundance was greater. Data were grouped into ten abundance classes and assessed for fit to the Poisson and negative binomial distributions. The Poisson distribution fit only data in abundance classes < 0.02 ticks per 10 m2, while the negative binomial distribution fit data from all abundance classes. A negative binomial distribution with common k = 0.3742 fit data in eight of the 10 abundance classes. Both the Taylor and Iwao mean-variance relationships were fit and used to predict sample sizes for a fixed level of precision. Sample sizes predicted using the Taylor model tended to underestimate actual sample sizes, while sample sizes estimated using the Iwao model tended to overestimate actual sample sizes. Using a negative binomial with common k provided estimates of required sample sizes closest to empirically calculated sample sizes.

Activity of Bacillus thuringiensis isolates against immature horn fly and stable fly (Diptera: Muscidae)

We screened 85 isolates of Bacillus thuringiensis (Berliner), making up 57 different subspecies, and two isolates of Bacillus sphaericus (Meyer and Neide) for activity against immature horn flies, Haematobia irritans (L.), and stable flies, Stomoxys calcitrans (L.). The majority of B. thuringiensis and the B. sphaericus isolates had little or no activity against horn fly and stable fly. Approximately 87% of the isolates caused < 50% mortality of horn fly larvae and 64% caused < 25% mortality. For stable fly, 95% of the isolates caused < 50% mortality, and 93% caused < 25% mortality. Five isolates were highly toxic to horn fly and stable fly immatures. These isolates were B. t. tolworthi 4L3, B. t. darmstadiensis 4M1, B. t. thompsoni 401, B. t. thuringiensis HD2, and B. t. kurstaki HD945. The LD50 values ranged from 2.2 to 7.9 x 10(6) spores per g manure for horn fly and from 6.3 to 35 x 10(6) spores per g media for stable fly. These were consistently more toxic compared with the B. t. israelensis isolates examined. All had DNA that hybridized with cry1Aa, cry1Ab, and cry1Ac toxin probes, three hybridized with a cry1B probe, and two hybridized with a cry2A probe. These may have potential for use in integrated management of pest flies.

Effect of grazing mixtures of alfalfa and orchardgrass grown in strips on the incidence of bloat in cattle

Steers were grazed on pastures with alfalfa and orchardgrass grown in monoculture strips with alfalfa covering 100, 75 or 50% of the ground area. The forages were maintained at an early stage of growth during the trial. The incidence of frothy bloat in cattle was reduced by 70 to 90% when grass was a component of the pasture. Given unconstrained free choice, the legume was preferred over the grass by steers. Key words: Steers, frothy bloat, Medicago sativa L., Dactylis glomerata L., mixed pastures, grazing

Tick paralysis caused by Dermacentor andersoni (Acari: Ixodidae) is a heritable trait

The heritability of the ability to cause paralysis was examined in crosses of virulent and avirulent Dermacentor andersoni (Stiles) (Acari: Ixodidae). Virulence was assessed using hamster bioassay. Paralysis was caused by the virulent parental strain but not by the avirulent parental strain. Four crosses were made: Avirulent female x Avirulent male (AA cross), Virulent female x Virulent male (VV cross), Avirulent female x Virulent male (AV cross), and Virulent female x Avirulent male (VA cross). The proportion of females that produced fertile egg masses was similar among the crosses; however, VV females produced fewer fertile eggs. This was attributed to the long-term laboratory colonization of the virulent strain. All crosses had similar levels of larval and nymphal engorgement and adult eclosion. The ability to cause paralysis was detected in progeny of all crosses except the AA cross. Both heterogeneous crosses caused paralysis, but the virulence was slightly less than for the VV cross. Virulence was similar among the AV and VA crosses, indicating that virulent males were as likely as females to pass the trait to progeny. Time to paralysis was faster for the VV cross compared with the heterogeneous crosses.

Species abundance and seasonal activity of mosquitoes on cattle facilities in southern Alberta, Canada

Seventeen mosquito species were collected at eight cattle facilities in southern Alberta, Canada, during 2002-2004. Five species, Culiseta inornata (Williston), Aedes dorsalis (Meigen), Culex tarsalis (Coquillett), Aedes vexans (Meigen), and Aedes campestris Dyar & Knab accounted for 93.6% of the mosquitoes collected. Culiseta inornata, Ae. dorsalis, and Ae. campestris were trapped earliest in the year. Cs. inornata was active latest in the year and had the longest period of activity. Ae. dorsalis finished activity in late September and had the second longest period of activity. Ae. campestris was the first to complete its activity, resulting in a moderate period of activity. Cu. tarsalis and Ae. vexans appeared later in the season, disappeared by late September, and had the briefest periods of activity. Logistic regression was used to estimate relationships between the proportions of traps positive and mean weekly abundance for each species. Fifty percent of the traps were positive when abundance averaged 0.19-0.30 females per trap night. Logistic regression was used to determine the timing of the onset of activity and temperature thresholds for flight. Relationships between the proportion of positive traps and mean weekly temperature indicated that Cs. inornata had the lowest temperature threshold, Cx. tarsalis the greatest, and the remaining species had intermediate thresholds. Logistic regression indicated that mosquito presence was primarily affected by temperature and accumulated degree-days, with only Ae. vexans exhibiting a positive response to precipitation. The models can be used to predict the onset of activity as defined by when populations exceed a particular threshold.

Species abundance and seasonal activity of mosquitoes on cattle facilities in southern Alberta, Canada

Seventeen mosquito species were collected at eight cattle facilities in southern Alberta, Canada, during 2002-2004. Five species, Culiseta inornata (Williston), Aedes dorsalis (Meigen), Culex tarsalis (Coquillett), Aedes vexans (Meigen), and Aedes campestris Dyar & Knab accounted for 93.6% of the mosquitoes collected. Culiseta inornata, Ae. dorsalis, and Ae. campestris were trapped earliest in the year. Cs. inornata was active latest in the year and had the longest period of activity. Ae. dorsalis finished activity in late September and had the second longest period of activity. Ae. campestris was the first to complete its activity, resulting in a moderate period of activity. Cu. tarsalis and Ae. vexans appeared later in the season, disappeared by late September, and had the briefest periods of activity. Logistic regression was used to estimate relationships between the proportions of traps positive and mean weekly abundance for each species. Fifty percent of the traps were positive when abundance averaged 0.19-0.30 females per trap night. Logistic regression was used to determine the timing of the onset of activity and temperature thresholds for flight. Relationships between the proportion of positive traps and mean weekly temperature indicated that Cs. inornata had the lowest temperature threshold, Cx. tarsalis the greatest, and the remaining species had intermediate thresholds. Logistic regression indicated that mosquito presence was primarily affected by temperature and accumulated degree-days, with only Ae. vexans exhibiting a positive response to precipitation. The models can be used to predict the onset of activity as defined by when populations exceed a particular threshold.

Inducing active and passive immunity in sheep to paralysis caused by Dermacentor andersoni

Arcott sheep were evaluated as a model for studying active and passive immunity to tick paralysis caused by Dermacentor andersoni (Stiles). The incidence of tick paralysis in sheep increased from 0 at doses < or = 0.33 ticks per kg to 100% at > or = 0.8 ticks per kg. The dose required for 50% paralysis was 0.42 ticks per kg. Expressing dose as a ratio of initial ticks per unit body weight removed differences in response due to sheep weight. The interval from infestation to paralysis decreased from >12 d at 0.4 ticks per kg to <8 d at 1.3 ticks per kg. After exposure to a paralyzing doses of ticks, the incidence of paralysis varied among sheep that were naive (six of six, 100% paralysis), previously paralyzed (zero of six, 0% paralysis), and passively immunized with an intravenous treatment of 300 ml of serum from immune cattle (two of six, 33% paralysis). Sheep that were actively immunized by previous exposure had antibodies to a greater number of tick salivary antigens compared with those that were not immune. Antibodies to a 43.3-kDa antigen had 72% agreement with immunity to paralysis, and a sensitivity and specificity of 0.60 and 0.88, respectively. In conclusion, previously paralyzed sheep had developed antibodies against D. andersoni and were not susceptible to subsequent paralysis, whereas passive immunization conferred protection against paralysis in only some sheep.

Cattle can develop immunity to paralysis caused by Dermacentor andersoni

Cattle exposed to a paralyzing strain of Dermacentor andersoni (Stiles) were all paralyzed during an initial exposure, but the incidence of paralysis decreased to 17 and 0% after two subsequent exposures to virulent flat ticks. Cattle with a single exposure to paralyzing ticks became paralyzed when challenged with ticks that had been prefed on cattle. Western blots indicated that cattle developed antibody responses to 13 antigens in paralyzing tick saliva. The likelihood of paralysis was inversely related to the number of saliva proteins that cattle developed antibody responses to. Cattle challenged with prefed ticks developed antibody response to fewer saliva antigens than cattle challenged with flat ticks. Variation in tick dose did not influence the expression of paralysis. Daily survival of ticks was similar on all groups of cattle, and tick weight was not reduced on previously challenged cattle, indicating immunity developed to the paralysis toxin rather than tick feeding. Four saliva antigens (molecular weights ranging from 36.9 to 42.2 kDa) were associated with the development of immunity to paralysis.

Reproductive compatibility of prairie and montane populations of Dermacentor andersoni

Genetic analysis of prairie and montane populations of Dermacentor andersoni (Stiles) originating from Alberta (AB) and British Columbia (BC), Canada, respectively, indicated limited gene flow (Nm <1) and a large amount of genetic differentiation (Fst = 0.49) between the populations. The prairie population also had a greater level of genetic diversity. Mating experiments indicated that females of geographically heterogeneous crosses had similar engorgement and oviposition failure as homogenous crosses in the parental generation but that egg mass sterility was greatest for the ABfemale x BCmale cross, intermediate for the homogenous crosses, and lowest for the BCfemale x ABmale cross. The progeny of all crosses produced fertile eggs, and the only significant effect in the progeny generation was increased oviposition failure of the pure AB cross. Covariate analysis indicated that egg mass sterility was associated with BC males in the parental generation and that oviposition failure was associated with AB males and AB females in the progeny generation. The hazard of cumulative reproductive failure was increased with AB females in both generations, reduced for AB males in the parental generation, and increased with AB males in the progeny generation. Overall, heterogenous crosses had the greatest and least reproductive failure in the parental generation, but they were intermediate to the homogenous crosses in the progeny generation. The limited gene flow between the populations seems to have been sufficient to maintain reproductive compatibility.

Reproductive compatibility of prairie and montane populations of Dermacentor andersoni

Genetic analysis of prairie and montane populations of Dermacentor andersoni (Stiles) originating from Alberta (AB) and British Columbia (BC), Canada, respectively, indicated limited gene flow (Nm <1) and a large amount of genetic differentiation (Fst = 0.49) between the populations. The prairie population also had a greater level of genetic diversity. Mating experiments indicated that females of geographically heterogeneous crosses had similar engorgement and oviposition failure as homogenous crosses in the parental generation but that egg mass sterility was greatest for the ABfemale x BCmale cross, intermediate for the homogenous crosses, and lowest for the BCfemale x ABmale cross. The progeny of all crosses produced fertile eggs, and the only significant effect in the progeny generation was increased oviposition failure of the pure AB cross. Covariate analysis indicated that egg mass sterility was associated with BC males in the parental generation and that oviposition failure was associated with AB males and AB females in the progeny generation. The hazard of cumulative reproductive failure was increased with AB females in both generations, reduced for AB males in the parental generation, and increased with AB males in the progeny generation. Overall, heterogenous crosses had the greatest and least reproductive failure in the parental generation, but they were intermediate to the homogenous crosses in the progeny generation. The limited gene flow between the populations seems to have been sufficient to maintain reproductive compatibility.

Effects of ambient temperature and cattle skin temperature on engorgement of Dermacentor andersoni

Experiments were conducted to determine whether changes in skin temperature of cattle held at ambient temperatures ranging from 10 degrees C to 30 degrees C influenced engorgement of female Dermacentor andersoni (Stiles). Average skin temperature of Angus cattle increased from 29 degrees C to 34 degrees C, whereas skin temperature of Holstein cattle increased from 32 degrees C to 35 degrees C over the range of ambient temperatures. Changes in skin and ambient temperature strongly influenced the proportion of ticks that successfully engorged, the time required for engorgement, and weight of engorged ticks, and they had a weaker influence on the proportion of dead ticks. The relationships between the tick engorgement parameters and ambient temperature differed between the experiments using either Angus or Holstein cattle. The differences between experiments were reduced when expressed in relation to skin temperature, suggesting that the thermal environment of the breeds is an important characteristic determining engorgement success. Results indicate that ticks respond to changes in the thermal environment of the host, and these changes may be important to engorging ticks exposed to fluctuating spring weather.

Seasonal abundance, parity, and survival of adult Culicoides sonorensis (Diptera: Ceratopogonidae) in southern Alberta, Canada

Culicoides sonorensis (Wirth & Jones) (Diptera: Ceratopogonidae) adults were active from May through October during 2002-2006 in southern Alberta, Canada. Adults were first captured in May, and populations peaked in early June, late July, and late August. The first population peak occurred when mean weekly temperatures exceeded 16 degrees C, resulting in a variable amount of time for spring emergence. This asynchrony in spring emergence accounted for much of the annual variation in timing of subsequent population peaks. Peaks were separated by an average of 6-7 wk. C. sonorensis seems to have one overwintering generation and two generations during the summer. Abundance was correlated among sites located up to 90 km apart. Abundance at a rangeland site increased more rapidly with mean weekly temperatures than at feedlot sites. The proportion female ranged from 0.68 to 0.83 but showed no consistent differences between rangeland and feedlot sites. The proportion female declined with distance from a developmental area at the rangeland site. Proportion parous was similar among rangeland and feedlot sites, and it also declined with distance from a developmental area at the rangeland site. The proportion parous increased early in the season, fluctuated throughout the mid-season, and increased with cooler temperatures in the fall. The proportion parous tended to increase when temperatures decreased. Estimates of adult daily survival were generally >0.8. Survival declined with temperature, was lowest in midsummer, and increased during the fall.

Effect of temperature on life history parameters of adult Culicoides sonorensis (Diptera: Ceratopogonidae) in relation to geographic origin and vectorial capacity for bluetongue virus

The effect of temperature on survival, oviposition, gonotrophic development, and a life history factor of vectorial capacity were examined in adult Culicoides sonorensis (Wirth & Jones) (Diptera: Ceratopogonidae) that originated from two geographic locations. Flies originating from the United States (Colorado) had slightly reduced survival after a bloodmeal compared with wild flies collected in southern Alberta (AB), Canada. Survival of AB flies declined in a curvilinear manner with temperature, whereas survival of U.S. flies showed a linear response to temperature. The survivorship curve of the AB flies more closely followed a Weibull distribution than an exponential, indicating survival was age-dependent. Survivorship of the U.S. flies followed an exponential distribution. Females from both sources laid similar numbers of eggs throughout their life. The first eggs were laid by females from both sources at 31.9 degree-day (DD)9.3. Dissections of blood-fed flies reared at various temperatures indicated that flies from both sources were 90% gravid at 32 DD9.3. Relationships among temperature and life history components of vectorial capacity were similar among flies from the two sources and indicated that vectorial capacity would be approximately 1.8-2.6-fold greater in a southern U.S. climate compared with southwestern Canada due solely to the effects of temperature on the life history of C. sonorensis. Using life history estimates derived from Weibull model had little effect on estimating vectorial capacity, whereas using estimates derived from the exponential model slightly overestimated vectorial capacity.

Abundance and species composition of Culicoides (Diptera: Ceratopogonidae) at cattle facilities in southern Alberta, Canada

Culicoides fauna was examined at seven feedlots and one rangeland site (Warner) in southern Alberta, Canada, during a 3-yr period. Eight species and species groups accounted for > 99% of the Culicoides (Diptera: Ceratopogonidae) captured. The most abundant species or groups were Culicoides gigas Root and Hoffman, Culicoides sonorensis (Wirth and Jones), Culicoides (Selfia) group, and Culicoides palmerae group. These accounted for 78-88% of the Culicoides captured, with the balance being members of the Culicoides cockerellii section, Culicoides crepuscularis Malloch, Culicoides wisconsinensis Jones, and Culicoides yukonensis Hoffman. Univariate and multivariate analyses indicated that the rangeland site was characterized by greater abundance of C. sonorensis and C. palmerae and lower abundance of C. (Selfia) compared with the feedlot sites. The Culicoides fauna was more dissimilar among sites as geographic distance between sites increased. Species of Culicoides captured in this study showed three broad patterns of seasonal abundance. The C. palmerae group had the earliest seasonal activity, with an increase in June, peak in July, and greatly reduced abundance thereafter. C. crepuscularis, C. (Selfia), C. wisconsinensis, and C. gigas had later periods of activity, with peak abundance in July, but moderate abundance in June and August. C. cockerellii, C. yukonensis, and C. sonorensis had the latest periods of activity, with populations increasing through June and July, peaking in August, and declining thereafter. C. sonorensis was somewhat unique on that it was the only species with moderate abundance as late as September.

Prefeeding Dermacentor andersoni (Acari: Ixodidae) on cattle with prior tick exposure may inhibit detection of tick paralysis by using hamster bioassay

The effect of prefeeding Dermacentor andersoni Stiles on naive and previously challenged cattle before conducting virulence assays by using hamsters was examined. In an initial observational trial, ticks prefed on a previously challenged heifer did not cause paralysis after transfer to hamsters, whereas ticks from the same lot that were prefed on a naive heifer did cause paralysis. Subsequent paired trails were conducted to simultaneously compare paralysis after feeding on naive and previously challenged heifers. In the first trial, prefeeding ticks on a previously challenged heifer did not result in loss of virulence. In a second trial, ticks fed on a previously challenged heifer had greatly diminished virulence after transfer to hamsters. This also occurred in a third trial after the previously challenged animal had two prior exposures to virulent D. andersoni. Weight gains of ticks that did not cause paralysis after transfer to hamsters were higher after feeding on previously challenged cattle, indicating that loss of virulence was not due to failure of ticks to reattach and feed. Ticks gained little weight on paralyzed hamsters due to the reduced time spent feeding on hamsters when paralysis occurred. Results indicate that assaying ticks for virulence requires prefeeding on naive hosts. If these are not available, rabbits, a resistant host, can be used for prefeeding ticks.

Retention of Escherichia coli by house fly and stable fly (Diptera: Muscidae) during pupal metamorphosis and eclosion

Populations of Escherichia coli obtained by feeding larval house flies, Musca domestica L. and stable flies, Stomoxys calcitrans (L.), persisted through the pupal stage. The abundance of E. coli in house fly pupae increased initially then declined before adult emergence. Abundance of E. coli in stable fly pupae increased through pupal development and remained high. Infected stable fly pupal cases typically contained more E. coli than house fly pupal cases. A greater proportion of emerging adult house flies were infected with E. coli compared with stable flies; however, the abundance of E. coli on infected flies was similar between species. Adult flies contained 0.04-0.19% of the E. coli in the pupal cases. The proportion of infected house fly adults and the amount of E. coli on the infected flies were related to the levels of E. coli in the pupal cases; however, these relationships did not occur with the stable fly. Results suggest that retention of E. coli from larval to adult house flies could play a role in the transmission and spread of E. coli, whereas stable fly adults probably play a minor role in E. coli spread. However, pupae of both species have potential to act as reservoirs for E. coli.

Persistence of Escherichia coli in immature house fly and stable fly (Diptera: Muscidae) in relation to larval growth and survival

The persistence of Escherichia coli in artificially fed larvae was examined for up to 48 h after ingestion by house flies, Musca domestica L., and stable flies, Stomoxys calcitrans (L.). The rate of change in the E. coli load was similar for both species for up to 5 h after ingestion. Up to 48 h after ingestion, abundance of E. coli declined in immature house flies but remained constant in immature stable flies. When different E. coli concentrations were fed to larvae, the abundance of E. coli increased in stable fly larvae regardless of the initial concentration. The E. coli load in house fly larvae increased when larvae were fed a low concentration of bacteria, but it declined when larvae were fed a high concentration of bacteria. Survival of house fly and stable fly larvae averaged 62 and 25%, respectively, when reared on pure E. coli cultures. These observations suggest that house fly larvae digest E. coli and use it as a food source but stable fly larvae do not.

Environmental effects on vector competence and virogenesis of bluetongue virus in Culicoides: interpreting laboratory data in a field context

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.

Effect of aggregation of horn fly populations within cattle herds and consequences for sampling to obtain unbiased estimates of abundance

Reanalysis of counts of horn fly, Hematobia irritans (L.), obtained from a variety of cattle herds indicated that aggregation of the flies within herds decreased as mean fly density increased. Aggregation was also related to the proportion of fly-resistant and fly-susceptible cattle in a herd. Herds were grouped according to their degree of horn fly aggregation. Low aggregation herds included larger framed Angus, Horned Hereford, Polled Hereford, and Red Poll breeds. Moderate aggregation occurred with Brahman, Charolais, small-framed Angus, mixed cows, and Hereford x Charolais cross. High aggregation occurred with Chianina and mixed herds. Relationships between the sample means and variances varied among aggregation groups. A resampling approach was used to determine the influence of random sampling of a herd on the proportion of horn fly population estimates within fixed percentages of the true mean. The proportion of sample means within +/- 5, 10, 15, and 20% of the true means varied with the proportion of the herd sampled, the mean and variance of fly density, and herd size. Recommendations for obtaining sample size to estimate fly density within a fixed percentage of the true mean are given.

Increasing the paralyzing ability of a laboratory colony of Dermacentor andersoni Stiles

Field-collected Rocky Mountain wood ticks Dermacentor andersoni Stiles from British Columbia caused limited paralysis in hamsters at high doses, but not at lower doses, while ticks collected from Alberta failed to cause paralysis. This prompted development of a laboratory strain of ticks with a more consistent ability to cause paralysis. Progeny of ticks that paralyzed a cow near Walhachin, British Columbia were reared and assayed for paralyzing ability. A high-virulence colony was selected for four generations using female ticks that cause paralysis singly on hamsters. A low-virulence colony was concurrently selected using female ticks that failed to cause paralysis at four ticks per hamster. Logistic regression indicated that the paralyzing ability of the high-virulence colony was consistently higher than that of the low-virulence colony, but that the paralyzing ability of both colonies increased through four generations of selection. Ticks required storage at 10 degrees C to terminate behavioral diapause. The effects of prolonged storage at 10 degrees C on the paralyzing ability of ticks was estimated and was small compared with differences between colonies and across generations. Single ticks from the high-virulence colony caused an increasing proportion of paralysis with each generation, but only limited paralysis with no increase across generations for the low-virulence colony. Single ticks from the high-virulence colony that caused paralysis were similar in weight and percent weight gain compared with single ticks that failed to cause paralysis. Engorged weight and egg mass production after four generations of rearing in the laboratory were similar to that measured for field-collected adults. Results indicated that laboratory selection could increase paralysis, but not eliminate it. This was likely a result of an inability to select male ticks.

Novel growth media for rearing larval horn flies, Haematobia irritans (Diptera: Muscidae)

Experiments were conducted to develop an agar-based medium for rearing immature horn flies, Hematobia irritans (L.). Larval survival was determined on sterilized manure inoculated with pure and mixed cultures of Acinetobacter sp., Bacillus pumilus Meyer & Gottheil, Comamonas acidovorans den Dooren de Jong, Pseudomonas mendocina Palleroni, Flavobacterium sp. and Empedobacter breve (Holmes & Owen). Rearing larvae on mixed cultures enhanced pupal weight but not survival. Horn fly larvae failed to survive when reared on standard bacteriological media inoculated with pure and mixed cultures of Acinetobacter sp., P. mendocina, and C. acidovorans. Larvae completed development on a minimal medium supplemented with alfalfa, egg proteins, and vitamins. Medium with low alfalfa content (30 g alfalfa/500 ml minimal medium) had enhanced survival when supplemented with egg yolk protein and vitamins. Medium with high alfalfa content (130 g alfalfa/500 ml minimal medium) had enhanced survival when supplemented with whole egg protein and vitamins. Survival was also favored when media were inoculated with pure cultures of Acinetobacter or Acinetobacter mixed with either Pseudomonas or Comamonas. Individual plates could support larvae developing from up to 40 eggs, and survival was least variable when plates were inoculated with greater numbers of eggs. This rearing system shows promise as a means for conducting standardized bioassays on a meridic diet.

Comparsion of selected growth media for culturing Serratia marcescens, Aeromonas sp., and Pseudomonas aeruginosa as pathogens of adult Stomoxys calcitrans (Diptera: Muscidae)

Stable flies, Stomoxys calcitrans (L.), were orally infected with Aeromonas sp., Pseudomonas aeruginosa (Schroeter), and Serratia marcescens Bizio that were cultured on egg-yolk media, nutrient broth, and fly egg media. Aeromonas and Serratia caused mortality when the bacteria were originally grown on egg-yolk medium. Pseudomonas was equally lethal regardless of the media on which it was cultured. A wild isolate of Aeromonas caused greater death than an isolate that had been passed through host flies and had been reisolated from killed flies. Mortality increased with bacterial dose for all species. Aeromonas and Serratia caused mortality within several days after ingestion, whereas Pseudomonas caused a gradual increase in mortality 3-7 d after ingestion. The pathologic activity of Aeromonas and Serratia required extracellular products produced when cells were grown in egg yolk medium. Aeromonas required both supernatant and cells from egg yolk medium, wereas Serratia required supernatant from egg yolk medium and cells from either nutrient broth or egg yolk medium. Mortality due to ingestion of Aeromonas was correlated with the presence of enzymes that cause alpha- and beta-hemolysis, while mortality following ingestion of Serratia was associated with alpha-hemolysins, elastases, and chitinases.

Growth and survival of immature Heamatobia irritans (Diptera; Muscidae) is influenced by bacterial isolated from cattle manure and conspecific larvae

Twenty species of bacteria were isolated from cattle manure and seven species were isolated from the gut of larval horn fly Hematobia irritans (L.). Bacteria in manure belonged to the Bacillaceae, Pseudomonadaceae, Micrococcaceae, Corynebacteriaceae, Enterobacteriaceae, Microbacteriaceae, and two unassigned genera. Gut bacteria belonged to the Enterobacteriaceae, Bacillaceae, Neisseriaceae, and Pseudomonadaceae. H. irritans larval survival and growth on the various bacterial species were evaluated by rearing larvae in sterilized cattle manure that was inoculated with single bacterial isolates. H. irritans larvae failed to develop in sterilized, uninoculated manure, indicating that bacteria are necessary for larval development. Survival averaged 74% in nonsterilized manure and ranged from 4 to 53% in manure with individual isolates. Survival was highest when larvae were reared on manure inoculated with Pseudomonadaceae, Corynebacteriaceae, Micrococcaceae, and Bacillaceae and was lowest when reared in manure inoculated with Enterobacteriaceae and Microbacteriaceae. Pupal weights were heaviest when reared on the Flavobacteria, followed by the Pseudomonadaceae and Corynebacteriaceae. Pupae averaged 4.9 +/- 0.08 mg when reared on gram-negative isolates, compared with 3.6 +/- 0.09 mg when reared on gram-positive isolates. Pupal weights were not significantly correlated with larval survival, indicating that bacteria that promote growth do not necessarily promote survival. A reproductive index was used as a measure of fitness and was highest for larvae reared in the nonsterile control, followed most closely by Pseudomonadaceae and Corynebacteriaceae. These groups appeared to best meet the nutritional requirements of larvae and may be used in further experiments to define an artificial rearing media for H. irritans.

Comparison of sample units for estimating population abundance and rates of change of adult horn fly (Diptera: Muscidae)

This study compared the reliability of population estimates of adult horn fly, Haematobia irritans (L.), obtained using different sample units. Mean-variance relationships were similar for abundance estimates obtained by counting flies on the sunny sides of cattle, on the upper body, and on the whole animal. Precision varied among the sample units, and was lowest for estimates obtained using the sunny side. Abundance estimates obtained using the sunny side and upper body sample units were related to estimates obtained using the whole body sample unit. However, the proportion of flies in the upper body and sunny side sample units declined with increasing fly density. Seasonal movement toward the belly accounted for this decline. This movement resulted in bias in estimating rates of change based on counting flies on the sunny side and upper body sample units. Rates of change based on sampling the sunny side were more biased than estimates based on the upper body sampling unit. Bias in estimating rates of change was examined using an analytical model compared with field data, and resulted from changes in the proportion of flies occupying the sample unit. Bias also increased with increasing actual rates of change. The implication of these findings for studying horn fly populations are discussed.

Rearing stable fly larvae (Diptera: Muscidae) on an egg yolk medium

The growth and survival of Stomoxys calcitrans (L.) larvae on egg yolk medium inoculated with bacteria isolated from a colony of stable flies was evaluated. Five species of bacteria--Acinetobacter sp., Aeromonas sp., Empedobacter breve (Holmes & Owen), Flavobacterium odoratum Stutzer, and Serratia marcescens Bizio--were identified according to fatty acid profiles using a microbial identification system. Larvae failed to develop on uninoculated plates, confirming that bacteria are required to complete development. Larvae also failed to complete development on plates inoculated with Aeromonas sp. and S. marcescens, and died during the 1st instar. Larvae completed development on the remaining 3 bacterial species as well as on Escherichia coli (Migula). Survival was generally higher when larvae were reared on Acinetobacter sp. and F. odoratum compared with E. coli and E. breve. Egg density did not influence larval survival, although the variability in survival was lowest using 20 and 40 eggs per plate. Larval survival in mixed cultures of Acinetobacter and Flavobacterium averaged 22.7% lower than survival in the pure cultures, and averaged 21.6% higher in mixed cultures of Empedobacter and Flavobacterium compared with pure cultures. Larval survival in mixed cultures did not differ significantly from mean survival in pure cultures for combinations of Acinetobacter and E. coli, Acinetobacter and Empedobacter, E. coli and Empedobacter, and E. coli and Flavobacterium. Larval developmental time was faster on all mixed bacterial cultures compared with developmental time on pure bacterial cultures. Optimal sample sizes and egg numbers are presented for detecting specified differences in larval survival. This rearing procedure will be useful for studying insect-microbe interactions and evaluating mortality using bacterial agents.

Relationships between temperature and life-history parameters of Stomoxys calcitrans (Diptera: Muscidae)

Relationships between temperature and life history parameters were determined for the stable fly, Stomoxys calcitrans (L.). Median immature developmental times ranged from > 60 d at 15 degrees C to < 12 d at 30 degrees C, with minimum time at 30.6 degrees C. Egg survival decreased from 0.98 at 15 degrees C to 0.91 at 20 degrees C, then increased to 0.98 at 35 degrees C. Larval survival ranged from 0.83 at 20 degrees C to 0.65 at 35 degrees C, and pupal survival ranged from 0.93 at 20 degrees C to 0.42 at 35 degrees C with maxima at 22.1 degrees C and 19.9 degrees C for larvae and pupae, respectively. Median longevity of females and males were greatest at 17.3 degrees C. Time to 50% survival ranged from > 30 d at 15 degrees C to < 6 d at 35 degrees C. Daily fecundity averaged 1.07, 8.89, 14.88, 26.22, and 7.90 eggs per female per day at 15, 20, 25, 30, and 35 degrees C, respectively. Lifetime fecundity ranged from < 30 eggs per female at 15 and 35 degrees C to > 700 eggs per female at 25 degrees C and was greatest at 25.3 degrees C. Net reproductive rate, and the intrinsic rate of increase had maxima at 25.3 and 27.8 degrees C, and mean generation time was minimum at 33.4 degrees C. Proportional variation in the time of immature development and adult longevity were independent of temperature, but proportional variation in the time of oviposition was related inversely to temperature. Extreme temperatures appeared to lengthen the preoviposition period and reduce the duration of egg production. Relationships were compared with previous studies. Equations developed and presented in this article will be used to develop a temperature-dependent stable fly population model.

Stable fly, Stomoxys calcitrans, mouthpart removal influences stress and anticipatory responses in mice

Biting fly attack induces a variety of stress and anxiety related changes in the physiology and behaviour of the target animals. Significant reductions in pain, or more appropriately, nociceptive sensitivity (latency of a foot-lifting response to an aversive thermal stimulus), are evident in laboratory mice after a 1 h exposure to stable flies, Stomoxys calcitrans. The role of the various components of biting fly attack in the development of this stress-induced reduction in pain sensitivity (analgesia) is, however, unclear. This study demonstrates that fly-naive mice do not exhibit a stress-induced analgesia when exposed to stable flies whose biting mouthparts have been removed. In contrast, mice that have been previously exposed to intact stable flies exhibit significant analgesia when exposed to flies that are incapable of biting. However, the level of analgesia induced is lower than that elicited by exposure to intact stable flies. Exposure to nonbiting house flies, Musca domestica, has no effect on nociceptive sensitivity. It appears that the actual bite of the stable fly is necessary for the induction of analgesia and probably other stress and anxiety associated responses in fly naive mice. However, mice rapidly learn to recognize biting flies and exhibit significant, possibly anticipatory analgesic responses to the mere presence of biting flies.

Influence of parasiticide treatment on kinetics of antigen specific antibody response in cattle infested with Hypoderma lineatum (Diptera:Oestridae)

The effect of parasiticide treatment on dynamics of antigen specific antibody responses to Hypoderma lineatum (De Villers) was investigated in naturally infested calves. Parasiticides were applied to cattle 1 month prior to, 1 week prior to, and coincident with the appearance of warbles in untreated calves from the same source herd. When cattle were treated approximately 1 month before warbles appeared in untreated control animals, antigen specific antibody levels increased for 25-34 days then declined to undetectable levels by approximately 75 days. Antigen specific antibody levels sharply declined in cattle treated 1 week prior to appearance of warbles in untreated controls. Treatment applied coincident with arrival of grubs on the back did not alter the antigen specific antibody profile, but reduced the relative magnitude of antigen specific antibodies present. Persistence of the antigen specific antibody following treatment will permit conduct of serological surveillance programmes.

Antibody responses in cattle infested with Haematobia irritans irritans (Diptera: Muscidae)

Antibody response to feeding by the horn fly, Haematobia irritans irritans (L.), was measured in naturally infested cattle as well as in controlled infestations. Humoral antibody level was not correlated with fly abundance in natural infestations. Correlations between the antibody response and fly abundance were extremely variable among animals. Antibody response to horn fly salivary antigens peaked within 4 wk after fly abundance reached 150 flies per animal. In controlled infestations, antibody response was weak during an initial exposure to 200 flies per animal, but increased after flies were removed from the cattle. Horn fly salivary antigen may have an immunomodulatory effect on the host.

Temperature and population density effects on feeding activity of Stomoxys calcitrans (Diptera: Muscidae) on cattle

The relationship of population density and temperature to feeding activity of stable flies, Stomoxys calcitrans (L.), on cattle was studied by placing cattle in constant temperature chambers with controlled fly density and temperature. The number of flies per front leg declined within hours after release but increased with fly density and temperature. The time flies spent on the host during a 5.5-h exposure period ranged from < 2.5 min at temperature < 16 degrees C to > 34 min when temperature was > 20 degrees C. Estimates of the temperature threshold for flight ranged from 10.7 to 20.1 degrees C and were influenced by density and time after release. Nearly 45% of the feeding flies were on the front legs, and this proportion was unaffected by density, temperature, and time after release. In the field, the number of flies per foreleg also was influenced by density and temperature. Estimated flight threshold was 10.7 degrees C, low enough to allow flight during 41-95% of the daylight hours from May through October in southern Alberta.

Seasonal abundance of stable flies and house flies (Diptera: Muscidae) in dairies in Alberta, Canada

Seasonal abundance of stable flies and house flies was studied at four dairies in southern Alberta, Canada, from May to October in 1989, 1990, and 1991. Stable flies were active from May to October in all years and showed population peaks in August and September. The weekly rate of change of stable fly populations was influenced by temperature and accumulated degree-days above 10 degrees C. The weekly rate of change of stable fly populations showed four peaks which were attributed to the emergence of an initial generation which had overwintered, followed by an additional three generations. Stable fly attacks on dairy cows occurred mainly from July through October, corresponding with the last two generations. House fly population abundance was much lower than stable fly populations and showed peaks in June, July, and September. Weekly changes in house fly abundance were not influenced by temperature and only weakly influenced by accumulated degree-days above 10 degrees C. Peaks in the weekly rate of change were associated with emergence of an initial, overwintering generation followed by four generations produced throughout the summer.