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.

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.

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.

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.

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.

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.

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.

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.