Bait Acceptance Research Articles

Attractiveness of bait matrices and matrix/toxicant combinations to the citrus pests Iridomyrmex purpureus (F.Smith) and Iridomyrmex rufoniger gp sp. (Hym., Formicidae)

Abstract: Six bait matrices were tested for palatability to the ants Iridomyrmex purpureus and I. rufoniger gp sp., which are important pests of citrus in south-eastern Australia. Granulated citrus pulp and rice bran impregnated with brown sugar were not accepted by either species, but ground dry dog food and ground insects (with or without added sugar) were highly attractive to both ant species. The ground dog food was impregnated with various toxicants at concentrations of up to 1% (w/w) and tested for palatability to both ant species. Technical grade pyriproxyfen, fipronil, and fenoxycarb were incorporated using organic solvents, whereas formulated fenoxycarb (Insegar®) was incorporated as an aqueous suspension prior to drying and granulation. Relative to the blank samples (carrier solvents only), bait acceptance by I. purpureus was not significantly reduced (P > 0.05) by any of the treatments except 1% technical fenoxycarb. Bait acceptance by I. rufoniger gp sp. was significantly suppressed by 0.2% fipronil, but not by higher concentrations. When water was used as the carrier solvent the blank sample was significantly (P < 0.05) less attractive to I. purpureus than the untreated control, suggesting that wetting of dog food-based baits in field situations may irreversibly reduce their attractiveness. Laboratory colonies were used in choice and no-choice tests to assess the efficacy of dog food baits containing fipronil (0.05–0.2% w/w). The corrected mortality for I. purpureus ranged from 88 to 100% and from 90 to 97% in the no-choice and choice tests, respectively. In no-choice tests I. rufoniger gp sp. corrected mortality varied from 52 to 60%, but in choice tests the corrected mortality did not exceed 26%. Ground dog food containing fipronil (0.05–0.2% w/w) has the potential to provide effective control of I. purpureus in citrus orchards, but alternative toxicants or lower fipronil concentrations may be required for control of I. rufoniger gp sp.

Assessment of hazards to non-native mongooses (Herpestes auropunctatus) and feral cats (Felis catus) from the broadcast application of rodenticide bait in native Hawaiian forests

Author(s): Dunlevy, Peter A.; Campbell, Earl W., III | Abstract: Primary non-target hazard assessment can be separated into two basic components: bait acceptance and toxicity. This bait acceptance study investigates the potential primary non-target hazard (direct consumption of bait pellets) that the broadcast application of rodenticide bait may pose to non-native feral cats and mongooses. The study was conducted in 4 different forest habitats in Hawaii using 2 different commercial formulations of placebo bait pellets. We documented vertebrates that came to placebo bait pellets at bait monitoring stations to assess bait acceptance. Bait pellets were monitored at each site using 40 infrared (IR) monitors/data loggers and weatherproof automatic cameras. During the 80 days of the study, cameras operated for 76,800 hours and recorded 21,211 slides of vertebrates at bait stations. Rodents, the target species, were the largest group, documented at stations in 98.98% (n = 20,994) of these photographs. Feral cats were detected in 0.09% (n = 20) and mongooses in 0.46% (n = 97) of the slides of vertebrates at bait pellets. The 117 photos of feral cats and mongooses represent 44 occasions where these predators encountered bait pellets; in 14 of these the bait was eaten. These data suggest that the primary hazard to non-native feral cats and mongooses from the broadcast application of pelletized rodenticides is very low. Thus, this study should support the effort to obtain regulatory approval for the broadcast application of rodenticide bait for conservation purposes in the state of Hawaii.

Rhodamine B as a systemic hair marker for assessment of bait acceptance by stoats (Mustela erminea)

Rhodamine B (RB) is a dye that becomes incorporated into the structure of growing hair of animals that ingest it, appearing as an orange‐red fluorescent band detectable under a fluorescent‐light microscope. This marker was evaluated as a means of assessing bait acceptance by stoats (Mustela erminea L.). Eleven wild‐caught captive stoats were each fed a broken hen egg injected with 25 mg of RB on two occasions, 5 weeks apart. This was equivalent to 62–108 mg kg–1, depending upon stoat weight, on each occasion. At least three facial whiskers were collected from each dosed stoat on each of two sampling dates (giving a total of at least six whiskers from each stoat). The sampling dates varied from 1 to 17 weeks after first dosing. Whiskers were also collected from one of the dosed stoats that died of other causes 19 weeks after first dosing, and from four stoats not dosed with RB. All 11 of the stoats fed RB had at least one fluorescent band in at least one of the sampled whiskers. None of the four stoats not fed RB had fluorescent bands in their whiskers. The marking persisted in all dosed stoats for at least 6 weeks, and in one dosed stoat for at least 19 weeks after dosing. However, only 56% of the 91 whiskers inspected from the dosed stoats had fluorescent bands, and only 9% of the whiskers had two fluorescent bands, representing the two doses of RB. The distance between the two fluorescent bands indicated a mean whisker growth of 0.6 mm day‐1. The distance from the base of the whiskers to the base of the fluorescent bands was broadly related to the time after ingestion of bait containing RB. However, the variation was too great for distance along the whisker to be reliably used as a quantitative measure of time after bait ingestion. The technique can be used to assess bait acceptance in the field provided all stoats are sampled within c. 4–6 weeks of baiting, and at least 6–9 whiskers are sampled from each stoat.

Iophenoxic acid as a systemic blood marker for assessment of bait acceptance by stoats (Mustela erminea) and weasels (Mustela nivalis)

Iophenoxic acid (IA) is a compound that causes an increase in the plasma and serum iodine concentration of animals that ingest it, and was evaluated as a marker for assessing bait acceptance by stoats and weasels. The baseline plasma or serum iodine concentration was measured in 12 captive and 10 wild stoats, and one captive weasel. Iophenoxic acid was mixed into broken hen eggs in amounts of 1, 2, 4, or 5 mg per egg (5 mg equals 0.01% in a 50 g egg), and the eggs were then fed to the captive animals. The mean plasma or serum iodine concentration in the dosed stoats was significantly higher than the mean baseline concentration (3.3 μg/100 ml) after 7 days (309.5 μg/100 ml) and after 14 days (24.0 ng/100 ml), but not after 21 days (6.4 μg/100 ml). The duration of plasma or serum marking in stoats (c. 2 weeks) was not as long as reported in most other studies of eutherian mammals (most more than 8 weeks). Not enough data were collected to determine the duration of marking in weasels.

Carbon disulphide for improving the efficacy of rodenticide baiting and trapping of the house rat, Rattus rattus L.

Rodenticide baiting and trapping are the common methods for the control of the house rat, Rattus rattus, which is a predominant commensal and agricultural pest throughout the tropic and sub-tropic regions of the world. During the present studies, a synthetic form of carbon disulphide (CS 2), which is considered to be an artificial semiochemical involved in mediating socially induced food choices, at its 0.5%, 1% and 2% concentrations in cereal bait (mixture of broken wheat grains, sugar powder and groundnut oil 96 : 2 : 2), attracted both male and female R. rattus in bio-choice feeding tests with individual rats and pen experiments with groups of 10 rats and also in field experiments in poultry house premises. Addition of 1% CS 2 in 2% zinc phosphide, 0.005% bromadiolone and 0.0025% difethialone baits significantly improved bait acceptance by R. rattus. (Corresponding values of per cent acceptance of scented bait over the unscented bait were 77.3, 74.2 and 65.9.) Similarly a greater number of rats were trapped with cereal bait containing 1% CS 2 than without it in pen and field experiments. In poultry houses CS 2-scented bait was effective in improving the trappability of rats during the first 3 days, after which it did not have a significant effect on the residual population.

A baiting system for delivery of an oral plague vaccine to black-tailed prairie dogs.

Laboratory and field studies were conducted between July and October 1999 to identify bait preference, biomarker efficacy, and bait acceptance rates for delivering an oral plague vaccine to black-tailed prairie dogs (Cynomys ludovicianus). Twenty juvenile captive prairie dogs were offered alfalfa baits containing either alfalfa, alfalfa and 5% molasses, or alfalfa, 5% molasses and 4% salt. Based on the results of these trials we selected a bait containing alfalfa, 7% molasses, and 1% salt for field trials to determine bait acceptance rates by free-ranging animals. The biomarkers DuPont Blue dye, iophenoxic acid, and tetracycline hydrochloride were orally administered to captive prairie dogs to determine their efficacy. Only tetracycline proved effective as a biomarker. Two field trials were conducted at separate prairie dog colonies located at the Buffalo Gap National Grassland (Pennington County, South Dakota, USA). In Trial 1, three baits containing tetracycline were distributed around each active burrow entrance and an additional bait was placed inside the burrow (1,276 baits total). In Trial 2, baits were distributed at the same density per burrow as Trial 1, but along transects spaced 10 m apart (1,744 baits total). Trapping began 3 days after bait distribution, and 30 prairie dogs then were captured at each site to determine the percentage of animals marked. In Trial 1, 67% of the prairie dogs captured had tetracycline deposits indicative of bait consumption. In Trial 2, 83% of the prairie dogs had ingested a bait. Approximately 15% of the animals in both trials ate more than one bait. Fleas (Opisocrostis hirsutus) were found on 64 of 70 (91%) of the prairie dogs captured during this study.

Carbon disulfide effects on pre-baited vs. non-pre-baited rats exposed to low dosage zinc phosphide rodenticide bait

Control of rodents with rodenticides is frequently ineffective due to bait-shyness and neophobia. In an initial study, to increase bait acceptance, Wistar-strain laboratory rats were individually tested for attraction to 3 odors (rat urine, preputial gland extract, and carbon disulfide) and for repellence to a fourth odor (coyote urine) in a 2-compartment arena. Three measures of rat preference-amount of bait consumed, elapsed time to feeding, and time in each compartment suggested that carbon disulfide at 10 ppm was an attractant ( p=0.003). The other odors produced inconsistent results. In a second study, rats were offered pre-weighed quantities of USA Environmental Protection Agency (EPA) standard challenge bait containing a low level of 0.20% zinc phosphide (ZP) rodenticide. Two groups of rats ( n=28) were given either 0 or 3 days of pre-baiting prior to ZP bait exposure. Half the animals in each group received deionized water placebo odor and the others received the carbon disulfide odor in the presence of baits. EPA bait with carbon disulfide odor produced elevated consumption ( p=0.0099) with females showing a greater degree of effect ( p=0.046). Pre-baiting produced higher mortality (220%) and higher level ZP dosages (30%) during baiting. Although mortality was 11% higher in rats presented ZP bait with carbon disulfide, dosages were unchanged. Relative to pre-baiting, the attractant had a marginal effect on ZP bait acceptance and produced mortality changes in males only. Further development of controlled release of this attractant for rodenticide baits would be needed before field applications are attempted; implications for using attractants in baits, traps, tracking powders to optimally control both rat genders are discussed.

Field trial with oral vaccination of dogs against rabies in the Philippines

BackgroundThe potential role of oral vaccination of dogs against rabies in the Philippines was investigated in terms of safety and efficacy.MethodsPrior to the vaccination campaign, a house-to-house survey was carried out to collect data on the dog population in the study area, the coastal village of Mindoro. During the vaccination campaign all households were visited again, and all dogs encountered (>2 months old) were, if possible, vaccinated. Furthermore, 14 dogs vaccinated were bled on different occasions.ResultsDuring the survey, a total of 216 dogs were counted, and none of these animals had previously been vaccinated against rabies. Only 17 dogs could be restrained and subsequently vaccinated directly by the vaccinators. Another 126 dogs were offered a local-made boiled intestine bait, containing a capsule filled with 3.0 ml SAD B19 (107.9 FFU/ml). The bait acceptance rate of dogs offered a bait was 96.1%. The vaccination coverage of the dog population (> 2 months old) estimated by the number of animals vaccinated directly and the number of dogs that accepted a bait and subsequently punctured the vaccine container was 76%. Fifteen and 29 days after the vaccination campaign 6 and 10 dogs (n = 14) had rabies virus neutralizing antibody titres of ≥ 0.5 IU/ml, respectively. No unintentional contacts of nontarget species, including humans, with the vaccine virus were reported.ConclusionsThe results of the campaign show that oral vaccination of dogs against rabies is a promising supplementary method in dog rabies control in the Philippines.

Seasonal marking efficacy of Dupont oil blue A dye on steam-rolled oat groat baits for valley pocket gophers

We examined if Valley pocket gophers ( Thomomys bottae) exhibited a seasonal preference for consuming steamed-rolled oat (SRO) groat bait treated with 1.6% Dupont oil blue A (fat-marking dye). Field tests were conducted in California alfalfa fields during winter, summer, and fall, and in walnut orchards during winter and summer. Five treatment units (TUs) were established each with ∼60 burrows for each season and habitat studied during 1997–1999. SRO groat marker bait (4 g) was placed inside each active burrow. All bait sites were re-opened about 96 h later and examined for the presence (all or some) or absence of bait. The average bait site disturbance after 4 days of baiting was 78.2%. Traps were used to capture gophers up to 5 days after baiting. Valley pocket gophers ( n=744) were examined for the presence of blue dye in their cheek pouches, skin/fur, and fat. We expected that if gophers moved the bait, their cheek pouches and fur would be marked; if they consumed bait, their fat would be marked. In alfalfa, 54.2%, 46.8%, and 65.7%, of gophers were marked (trapping on days 5–9) by blue dye in one or more of their cheek pouches, skin, fur, or subcutaneous fat in the winter, summer, or fall, respectively. In orchards, 57.1% of gophers were marked in winter and 53.4% in summer. Of those that were marked, all (100%) had their fat dyed blue, followed by skin/fur (34.4% males : 43.7% females) and cheek pouches (5.7% males : 10.1% females) . ANOVA results indicated no difference in seasonal marking efficacy in either alfalfa or orchards ( F=3.59, P=0.0598 and F=0.12, P=0.7384, respectively). The usefulness of 1.6% Dupont oil blue A dye as a marking agent for Valley pocket gophers was not demonstrated overall or for any season in either habitat. Therefore, a better marker for this gopher is needed. Some factors that may have influenced these results were discussed including: (1) baiting methodology (∼66% of the bait sites were devoid of bait at the end of the study), (2) species specific dye properties, (3) bait acceptance (i.e. aversion to the dye), or (4) availability of alternative foods.

Oral Rabies Immunization of Swine: Use of Vnukovo-32/107 Vaccination Strain

Ondrejka R., A. Ondrejkova, ·. ·vraek, Z. Beni‰ek, J. Suli, J. Zavadova, M. Maiar, J. MojIi‰ova: Oral Rabies Immunization of Swine: Use of Vnukovo-32/107 Vaccination Strain. Acta Vet. Brno 2001, 70: 333–338. The apathogenicity and antigenic activity of the live oral rabies vaccine prepared from the strain Vnukovo-32/107 were evaluated in two experiments carried out on non-target species – swine (domestic swine Sus scrofa domestica and wild boar Sus scrofa). The Vnukovo-32/107 vaccination strain has been used to produce oral rabies vaccine Kamark for immunization of free living carnivores. Wild boars compete with foxes for acceptance of baits distributed in the field. The tested vaccination strain for oral application (including very high doses) proved apathogenic to non-target species – swine. Detection and quantification of rabies antibodies were carried out by an immunoenzymatic assay – ELISA, rapid fluorescence focus inhibition test (RFFIT) and virus neutralization test (VNT) on mice on days 30 and 90 post-immunization. The values obtained were expressed in international units (IU/cm3); the value of 0,5 IU/cm3 was used as a positivity criterium. Antirabic antibodies were detected in more than 50 % of animals in all three groups of two animal sets on day 30 post-immunization. The results obtained show good antigenic activity of the live oral rabies vaccine prepared from the strain Vnukovo-32/107. Rabies, vaccination strain Vnukovo-32/107, apathogenicity; antigenic activity

Evaluation of control measures for black carpenter ant (Hymenoptera: Formicidae).

Current control methods for the black carpenter ant, Camponotus pennsylvanicus (De Geer), include the use of remedial and preventative residual sprays as well as toxic baits. We evaluated the acceptance of three baits (Maxforce, Niban, and Baygon) to field colonies of the black carpenter ant in the spring and fall. Maxforce bait granules were more readily accepted than either Niban or Baygon bait granules in the spring. A change in food preference from protein to sugar by the black carpenter ant appeared to reduce the number of Maxforce bait granules removed in the fall, resulting in no differences in bait acceptability. The longevity of Dursban 50W and Tempo 20WP were evaluated in the summer and fall on painted wood panels. Panels aged outside for 15 d under prevailing weather conditions exhibited increased LT50 values. For each sampling period, panels aged on the south face (in the sun) exhibited less insecticidal activity (i.e., large LT50 values) than panels on the north face (shaded; small LT50 values). At each sampling period, Tempo 20WP provided smaller LT50 values than Dursban 50W. Because of changing dietary preferences, our data highlight the importance of using various bait types for carpenter ant control. Moreover, the application of residual spays should be made to locations protected from direct sunlight.

Use of zinc phosphide for California ground squirrel control

Zinc phosphide (ZnP) is the only acute rodenticide currently registered for control of the California ground squirrel (Spermophilus beecheyi). Research has shown ZnP to give excellent control of sciurid rodents, but operational control programs in California have reported poor and inconsistent control. We examined the literature and conducted 34 field trials between 1996 and 1999 in order to identify factors affecting the field efficacy of ZnP. Important factors identified from the literature include bait acceptance, prebaiting, and timing of control operations in relation to ground squirrel and vegetation phenology. We used ground squirrel counts or active burrow counts to assess the efficacy of ZnP in the field trials. Treatments were either mechanical broadcast or spot baiting of 2% ZnP-treated oat groats. The first field trials in 1996 and 1997 were conducted without bait acceptance tests and prebaiting, and control was inconsistent, ranging from none on one plot, poor on three plots (45% to 63%), to good on two plots (84% to 87%). Field trials in 1998 and 1999 were conducted with bait acceptance tests and pre-baiting. In 1998 control was excellent (88% to 100%) on all plots. However, control was variable in 1999 trials with good control (80% to 90%) on five plots, but poor control (60% to 79%) on two plots, and no control on one plot. In our studies, pre-baiting had little effect on the efficacy of the ZnP for controlling California ground squirrels.

Evaluation of attractants and bait preferences of captive red foxes (Vulpes vulpes)

The development of bait types, additives such as synthetic flavours, and attractants for use in fox control and rabies vaccination programmes is briefly reviewed. A captive colony was used to establish bait preferences for foxes. A variety of bait types and additives were screened for this purpose. The potential of chemical attractants to enhance the discovery of baits by foxes was also examined. Gustatory additives, such as beef flavour and sugar, enhanced bait acceptance, and olfactory attractants such as synthetic fermented egg showed promise. Trials using captive animals allow for observations impossible under field conditions. However, field trials are also needed to determine whether behavioural responses of free-ranging animals are similar to those observed in captive individuals.

Stabilization of the avicide 3-chloro-p-toluidine as the beta-cyclodextrin adduct.

Stabilization of the avicide 3-chloro-p-toluidine (CPTH) on rice baits by pseudo latex polymeric coating and beta-cyclodextin inclusion was investigated. When CPTH-treated rice baits were exposed to sunlight, the CPTH formed colored compounds, which exacerbated problems with bait acceptance and efficacy. Fluidized bed coating with controlled-release polymeric psuedo latexes (RS, RL, NE) reduced CPTH loss but did not eliminate color formation. Enteric pseudo latex coatings (CAP and 4110) gave mixed results. Coating 4110 reduced CPTH loss but still allowed color formation, whereas CAP allowed more CPTH loss than any other coating as well as increased color formation. Inclusion in beta-cyclodextrin (molar ratio 1:1) led to enhanced retention of CPTH and minimal color formation. The CPT/beta-cyclodextrin adduct increased retention of CPTH from 43 to 70% upon simulated weathering. The retention was independent of the adhesives used for attachment.

Pre‐baiting for increased acceptance of zinc phosphide baits by voles: an assessment technique

During a product-performance test of 2% zinc phosphide (Zn3P2) steam-rolled-oat groats (11.2 kg ha−1) to control voles (Microtus spp) in alfalfa (Medicago sativa), randomly located, brushed-dirt plots were used to assess broadcast distribution and removal/acceptance of placebo particles. Results showed that the Spyker® Model-75 Spreaders were calibrated adequately, with placebo baits broadcast uniformly onto plots [x ± SD = 3.5 (±2.7) groats 930 cm−1]. Acceptance of the placebos by voles increased rapidly – 28% and 60% by 24 h and 48 h post-broadcast, respectively. Analyses of variance confirmed the uniformity (non-significance) of particles broadcast among enclosures/plots and the significantly greater removal/acceptance of placebos across days. This technique affords an objective decision-making tool for applicators and researchers applying Zn3P2 baits in field situations – an objective technique of assessing pre-bait acceptance that should improve efficacy of the rodenticide. © 1999 Society of Chemical Industry

Pre-baiting for increased acceptance of zinc phosphide baits by voles: an assessment technique

During a product-performance test of 2% zinc phosphide (Zn 3 P 2 ) steam-rolled-oat groats (11.2 kg ha -1 ) to control voles (Microtus spp) in alfalfa (Medicago sativa), randomly located, brushed-dirt plots were used to assess broadcast distribution and removal/acceptance of placebo particles. Results showed that the Spyker® Model-75 Spreaders were calibrated adequately, with placebo baits broadcast uniformly onto plots [x±SD=3.5 (±2.7) groats 930 cm -1 ]. Acceptance of the placebos by voles increased rapidly - 28% and 60% by 24h and 48h post-broadcast, respectively. Analyses of variance confirmed the uniformity (non-significance) of particles broadcast among enclosures/plots and the significantly greater removal/acceptance of placebos across days. This technique affords an objective decision-making tool for applicators and researchers applying Zn 3 P 2 baits in field situations - an objective technique of assessing pre-bait acceptance that should improve efficacy of the rodenticide.

Pre-baiting for increased acceptance of zinc phosphide baits by voles: An assessment technique

Pre-baiting for increased acceptance of zinc phosphide baits by voles: An assessment technique

Bait uptake by foxes (Vulpes vulpes) in urban Melbourne: the potential of oral vaccination for rabies control

Red foxes (Vulpes vulpes) are widely distributed throughout the Melbourne metropolitan area. Density estimates indicate that fox populations would be capable of maintaining the endemic persistence of rabies. Oral vaccination of foxes by baiting is a technique that has been used successfully overseas to manage rabies epizootics. This study assessed the uptake by foxes of baits containing biomarkers in three urban field sites in winter 1993 and summer 1993/94. Baits were dosed with 200 mg of tetracycline in the winter trial and 5 mg of iophenoxic acid in the summer trial, and distributed at a density of 8 baits ha −1 in open areas within each field site. In the winter trial, 8 of 11 (72.7%) radio-collared foxes known to be in the field sites during the distribution of baits were marked. In the summer trial, 45 of the 49 foxes (92%) recovered from the combined field sites had consumed at least a single bait, resulting in bait acceptance of 80–97% for each field site. No bias existed between plasma iodine levels due to sex, although first-year foxes had a significantly higher level than older age groups combined. There were no significant differences in mean age of foxes collected at the three field sites, yet significant differences existed in mean plasma iodine concentrations between all three sites. These results are discussed with reference to rabies contingency planning. The high rates of bait uptake in this study are encouraging and suggest that oral vaccination may be a viable strategy for rabies containment in urban areas and is worthy of further assessment at reduced baiting densities.

Evaluation of strychnine and zinc phosphide baits to control northern pocket gophers ( Thomomys talpoides) in alfalfa fields in Alberta, Canada

This study compared the effectiveness of Sanex 0.40% strychnine-treated oats, Fairview 0.37% strychnine-treated grains, and United Agri Products 2% zinc phosphide-treated oats to control northern pocket gopher ( Thomomys talpoides) populations in alfalfa fields in Alberta, Canada. The poison baits were tested during three phenological periods corresponding to the reproduction, summer juvenile dispersal, and early fall mound building activities. Overall, less than 17% of the pocket gopher populations were controlled by any poison bait during the reproduction and early fall periods. In summer, there was a significant difference ( P < 0.05) between poison baits as measured by the relative frequency of active and inactive burrow systems. The Sanex poison bait was significantly ( P < 0.05) more effective (36%) in terms of reduced pocket gopher activity than the other baits (≤ 15%). I suggest that the effectiveness of poison baits to control pocket gophers may be greater in mid-summer after hay harvest, when the young of the year disperse to establish their own burrow system. However, because of the overall poor performance of all tested poison baits in alfalfa fields, more research and development work based on animal behaviour should be carried out to improve bait acceptance.

Results of an oral rabies vaccination program for coyotes

Objective To determine effectiveness of large-scale distribution of an oral rabies vaccine contained in a palatable bait for halting expansion of a canine rabies epizootic in coyotes (Canis latrans). Design Prospective study. Animals 98 coyotes during prevaccination surveillance and 449 coyotes and 60 other wild animals during postvaccination surveillance. Procedure A vaccinia recombinant oral rabies vaccine was inserted into an edible bait for coyotes that also contained tetracycline as a biomarker. Vaccine units were then distributed via aircraft, using automated distribution equipment and flight plans developed by incorporating global positioning system equipment. The target area was along the northern edge of an area that had an epizootic of canine rabies. This area was identified through previously conducted epidemiologic surveillance of rabies cases. During postvaccination surveillance, dental specimens were examined for biomarker evidence of bait acceptance, and serum samples were analyzed for rabies neutralizing antibodies. Results Samples from 449 coyotes were obtained during postvaccination surveillance. Seroconversion was detected in 39 of 96 (40.6%) coyotes that had evidence of tetracycline biomarker. Additionally, the number of rabies cases in the target area decreased, and expansion of the epizootic area ceased. Clinical Implications Mass distribution of an oral rabies vaccine in a palatable bait is an effective means to halt expansion of a rabies epizootic involving coyotes. (J Am Vet Med Assoc 1998; 212:498-502)