Baiting Strategies Research Articles

Specificity and success of oral-bait delivery to Eurasian wild boar in Mediterranean woodland habitats

Eurasian wild boar (Sus scrofa) is an important reservoir host for pathogens affecting humans and domestic animals. The eradication of these diseases may require the development of control strategies that reduce pathogen transmission between wildlife and domestic animals. Baiting for oral vaccine delivery is often considered for wildlife disease control. The effective and efficient field vaccination of wildlife requires species-specific baits as delivery vehicles for oral vaccines and designing appropriate baiting strategies. The objective of this study was to determine the proportion of young and adult wild boar and non-target animals that consumed baits containing a chemical marker, iophenoxic acid (IPA), in delivery trials conducted in summer in four different sites in the Mediterranean region of Spain where wild boar are abundant. The proportion of wild boar showing IPA markers in serum in autumn ranged from 11.5% to 56.4%. When attending to age classes, 12.6% to 72.7% of young individuals presented IPA. The results evidenced that the percent of wild boar that ingested the baits varied among study sites and age classes. Placing baits inside selective cages (for juveniles) and under heavy pavel stones (for adults) contributed to improve age specificity in bait consumption. We suggest ways for improving the age specificity of bait delivery systems used for young and adult wild boar.

The impacts and management of foxes Vulpes vulpes in Australia

1. The successful introduction of the red fox Vulpes vulpes into Australia in the 1870s has had dramatic and deleterious impacts on both native fauna and agricultural production. Historical accounts detail how the arrival of foxes in many areas coincided with the local demise of native fauna. Recent analyses suggest that native fauna can be successfully reintroduced to their former ranges only if foxes have been controlled, and several replicated removal experiments have confirmed that foxes are the major agents of extirpation of native fauna. Predation is the primary cause of losses, but competition and transmission of disease may be important for some species. 2. In agricultural landscapes, fox predation on lambs can cause losses of 1–30%; variation is due to flock size, health and management, as well as differences in the timing and duration of lambing and the density of foxes. 3. Fox control measures include trapping, shooting, den fumigation and exclusion fencing; baiting using the toxin 1080 is the most commonly employed method. Depending on the baiting strategy, habitat and area covered, baiting can reduce fox activity by 50–97%. We review patterns of baiting in a large sheep-grazing region in central New South Wales, and propose guidelines to increase landholder awareness of baiting strategies, to concentrate and coordinate bait use, and to maximize the cost-effectiveness of baiting programs. 4. The variable reduction in fox density within the baited area, together with the ability of the fox to recolonize rapidly, suggest that current baiting practices in eastern Australia are often ineffective, and that reforms are required. These might include increasing landholder awareness and involvement in group control programs, and the use of more efficient broadscale techniques, such as aerial baiting.

Evaluation of an oral vaccination program to control raccoon rabies in a suburbanized landscape

We evaluated the efficacy of an oral rabies vaccination (ORV) program conducted in Erie County, New York, from July through September, 2002–2005. Ingress of the raccoon (Procyon lotor) rabies variant first occurred along the southern border of Erie County, New York, during 1992 and began to spread northward at a velocity of 31 km/year. Fixed-wing aircraft dropped ORV baits in rural landscapes; helicopters, hand baiting, and bait stations distributed baits in suburban landscapes ( bait densities ranged 59–118 baits/km2). Our study objectives were to quantify rabies case densities, evaluate efficacy of intervention efforts, and determine biological, census, geographical, and weather variables potentially affecting oralrabies vaccination of raccoons in Erie County. Overall, 16% and 9% of the raccoons in Erie County tested positive for virus-neutralizing antibodies (VNA) at the 0.125 and 0.5 international units (IU)/ml levels, respectively. We found no differences between baiting strategies and frequencies of antibody-positive raccoons. However, adult males generally consumed baits most often, and the probability of seropositivity increased with raccoon age. Seroprevalence of VNA differed among raccoon sex and age classes, and vaccination year. A post-hoc kernel density estimation of rabies-positive raccoons and skunks (Mephitis mephitis) from 1992– 2006 (n = 364) revealed clustering in northeastern Erie County. Our results should help ORV managers maximize limited resources.

Effects of Natural Barriers and Habitat on the Western Spread of Raccoon Rabies in Alabama

Abstract: Although domestic animal transmission of rabies has largely been mitigated, the disease remains a concern in both Europe and North America where wildlife transmission has caused epizootics. Raccoon (Procyon lotor) rabies was established in Alabama, USA, in 1975, primarily in the southeastern corner of the state. However, with the exception of isolated events, rabies has not continued to spread westward across the Alabama River. We monitored movements of 100 radiocollared raccoons on 2 sites within hardwood and agriculture habitats in a rabies enzootic area east of the Alabama River, in managed pine habitat area west of the river where rabies sporadically occurs, and in a mixed pine hardwood area outside of the known rabies enzootic area to determine if raccoon movements and habitat use in certain habitat types and the presence of a river may serve as natural barriers preventing the western spread of rabies in Alabama. We also examined raccoon contact rates to determine if they influence disease transmission through static and dynamic interactions. Raccoons in mixed pine‐hardwood forest habitats had smaller home ranges and less overlap of ranges compared to the other 3 habitats. However, static interactions between habitats in the use of overlap areas did not differ (F11,129 = 1.63, P = 0.09). Rabies antibody titers were highest in the managed pine habitat (28%) even prior to oral vaccine bait distributions in spring of 2004 and 2005. Biomarker data from radiocollared and additional raccoons captured after the bait distribution west of the Alabama River demonstrated a low efficacy of the vaccine reaching the small southern raccoons. The combination of the river as a partial barrier, the high percentage of pine forested habitat west of the river, and limited spatial movements of raccoons within these forested habitats appears to have reduced the likelihood of rabies establishing west of the river. Understanding different host‐habitat‐ disease systems is important for successful management of diseases. Based on our results, we recommend that the oral vaccine program continue to use the Alabama River as a partial barrier and baiting be concentrated in the fragmented bottomland hardwood forests and around larger bodies of water where raccoon densities are highest. Success of baiting strategies designed to take advantage of northern raccoon dynamics and habitat use may not be applicable to southern populations.

Comparison of Suburban Vaccine Distribution Strategies to Control Raccoon Rabies

Helicopters and hand baiting are commonly used to distribute vaccine-laden baits to help control raccoon (Procyon lotor) rabies in suburban landscapes, but these techniques may be labor intensive, costly, or unavailable in some areas. We tested conventional baiting strategies against polyvinyl-chloride (PVC) bait stations in Erie County (New York, USA) during July and August 2003-05. Hand, helicopter, and bait station treatments were randomly assigned to six 25-km(2) suburban study sites. To estimate the proportion of raccoons that ingested baits, tooth and blood samples from 954 raccoons were collected and examined for tetracycline biomarker and rabies-neutralizing antibodies, respectively. Overall, 38% (358/954) of the raccoons in Erie County tested positive for tetracycline; 16% (155/954) tested seropositive for rabies virus. Year of study significantly impacted biomarker prevalence; fewer raccoons tested positive for tetracycline in 2004. Probability of seropositivity increased with raccoon age. No statistically significant differences existed between baiting strategies and frequencies of biomarker and antibody-positive raccoons across all years combined. Thus, bait stations could be used as part of an integrated rabies control strategy.

Feasibility of oral rabies vaccination campaigns of young foxes (Vulpes vulpes) against rabies in summer

Oral vaccination of foxes (Vulpes vulpes) against rabies has been shown to be highly effective. Several baiting strategies to increase vaccination coverage of the target population have been developed. For example, to increase the vaccination coverage of the young fox population before dispersal an additional summer vaccination campaign has been suggested. The effectiveness of such a campaign was evaluated using field data on home range size and shape of young foxes and a simulation model for aerial bait distribution. The results indicated that the limited ranging behaviour of the young fox population during the summer months severely reduced bait accessibility and consequently such an additional vaccination campaign would be very cost-ineffective.

Grower Evaluation of California Ground Squirrel (Spermophilus beecheyi) Control using Anticoagulant Baits

Author(s): Kowalski, Victor J.; Long, Rachel; Sullins, Jim; Garcia, Sergio; Salmon, Terrell P. | Abstract: California ground squirrels continue to present a significant problem for many facets of California agriculture. The use of diphacinone- and chlorophacinone-treated baits remains the most frequent control method for ground squirrels in agricultural settings. Research suggests no difference in efficacy between the two bait types or between broadcast and spot baiting strategies or bait stations. However, these studies were limited in scope and were conducted exclusively on rangeland sites where there is limited availability of alternate food sources. Studies also suggest that a reduced baiting strategy may be as effective as current label recommendations, but this has received only limited attention in field research. We utilized a new approach in conducting field evaluations of anticoagulant baiting efficacy in different agricultural settings and locations throughout the state. We solicited agricultural producers as cooperators to participate in a field-based evaluation to determine if the reduced baiting strategies are effective under specific agricultural operating conditions. Cooperators were trained in a simple research design and monitored to ensure consistent data collection. The training program included a comprehensive manual on squirrel biology, behavior, and control, as well as information on toxicants and legal measures regarding endangered species. An informal survey was sent to cooperators at the end of the project to evaluate their opinions on the efficacy of control methods. We found no difference in efficacy between baiting methods or strategies. Differences in efficacy were found between chlorophacinone and diphacinone and efficacy was lower in nut orchards than in other settings. Despite no difference in efficacy between baiting methods, more cooperators indicated they would use bait stations than other methods in future ground squirrel control operations.

Anticoagulant Resistance in Meadow Voles (Microtus californicus)

The California meadow vole, Microtus californicus, is a major vertebrate pest in artichoke fields of Castroville, California. Complaints from growers about the effectiveness of the only available rodenticide, chlorophacinone treated artichoke bracts, led researchers to the test the bait and baiting strategies. When laboratory trials were conducted in 2001, the poor dose-response correlation and apparent low sensitivity to chlorophacinone in some animals suggested the possibility of anticoagulant resistance. The current study was initiated to examine potential resistant of voles from artichoke fields in the Castroville area. Baseline blood coagulation data were obtained from wild, anticoagulant-susceptible voles trapped in Yolo County, California and compared to data from Castroville voles. Results indicate a significant difference in clotting times 24 hours after dosing with anticoagulant between voles from Castroville artichoke fields and voles from the Yolo population. This supports the hypothesis that voles from Castroville artichoke fields are resistant to anticoagulants.

Attractiveness of a novel omnivore bait, PIGOUT®, to feral pigs (Sus scrofa) and assessment of risks of bait uptake by non-target species

Following a bait-preference pilot study on captive feral pigs, a series of field studies assessed the attractiveness and target-specificity of a prototype manufactured feral pig bait (PIGOUT®). Two promising test baits and fresh meat reference baits were biomarked with iophenoxic acid and aerially distributed in 100-km2 blocks of land infested with feral pigs in western Queensland to assess field uptake and target-specificity without prefeeding. Uptake was assessed by measuring blood iodine levels in aerially shot feral pigs. In all, 80% of feral pigs sampled in a non-toxic PIGOUT®-baited area had significantly elevated blood iodine, compared with 52% of sampled feral pigs in a meat-baited area (although slightly different baiting strategies were employed). No age or sex bias was evident in PIGOUT®-consuming feral pigs. No monitored manufactured baits were consumed by non-target species in 500 bait-nights. Attractiveness and target-specificity trials of ground-laid, unfenced PIGOUT® baits compared with reference baits were subsequently undertaken in several regions of eastern Australia. Results showed that PIGOUT® was consumed readily by feral pigs at all sites, and that it offered significant improvement in target specificity when compared with unfenced wheat or meat baits. However, the baits were consumed by small numbers of macropods, birds and possums. Available evidence indicates that the target-specificity of PIGOUT® bait is highest in the rangelands, reducing slightly in temperate areas and subalpine forests, where abundance of small animals is higher.

Probabilistic Model to Optimize Formulation and Baiting Strategies for the Pesticide CPTH (3-chloro-4-methylaniline hydrochloride)

A probabilistic model was validated for estimating avian mortality associated with the application of the avicide CPTH (3-chloro-4-methylaniline hydrochloride) to minimize sprouting rice damage in the southern United States. CPTH exposures for individual birds were predicted by random sampling from species-specific non-parametric distributions of bait seed consumption and CPTH residues detected on individual bait seeds. Mortality was predicted from the species-specific exposure versus mortality relationship. Individual variations in this response were captured in the model by Monte Carlo sampling from species-specific distributions of slopes and median toxicity values (LD 50 ) for each bird. The model was used to evaluate the effects of formulation, bait preparation and application procedures on target and non-target mortalities. The results of these analyses indicate that: 1) decreasing the concentration of CPTH on the treated bait seeds from 400 to 300 µg CPTH/seed will improve bait performance by decreasing non-target mortalities, 2) the current dilution ratio of 1 treated seed to 25 diluent seeds is optimal and 3) preparing a bait seed product in which CPTH is homogeneously distributed throughout the bait seed mixture will significantly increase bait performance by increasing red-winged blackbird (target) mortality and decreasing mortality for savannah sparrows and meadowlarks (non-targets).

Increasing acceptance and efficacy of zinc phosphide rodenticide baits via modification of the carbohydrate profile

Toxicant coated grain-based baits are widely used to control rodent pests throughout the world, but where alternative food sources are available, bait acceptance and efficacy are often less than optimal. In an attempt to develop baiting strategies to increase bait acceptance and efficacy of zinc phosphide-coated baits, a sugar-enhanced rolled oat based zinc phosphide bait was evaluated. With pre-baiting, 100 and 60% mortality was achieved for California and Belding's ground squirrels, respectively. A series of two-choice tests with a variety of potential bait matrices indicated that rolled oats was a desirable base matrix for both species but the lecithin sticker negatively impacted bait acceptance by Belding's ground squirrels.

BAITING RED FOXES IN AN URBAN AREA: A CAMERA TRAP STUDY

Baiting red foxes (Vulpes vulpes) is an established method of vaccinating foxes against rabies in rural environments. Furthermore, anthelmintic baiting has been demonstrated to reduce the prevalence of the zoonotic tapeworm Echinococcus multilocularis in foxes. The recent invasion of foxes into urban areas on continental Europe represents a considerable health risk that calls for the evaluation of baiting strategies adapted to the urban environment. We investigated bait uptake by urban foxes using camera traps in Zurich, Switzerland. Baits with and without the anthelmintic praziquantel were placed in several arrangements (exposed, covered, buried), at different locations (fox dens, compost heaps, fox tracks) and in different seasons (early summer, summer, winter). Ninety-one of 252 baits (36%) disappeared within 3 days. Most of the baits consumed near cameras were consumed by foxes (44 of 91). The remaining baits were consumed by hedgehogs (Erinaceus europaeus), snails (Arion sp.), dogs, rodents (Apodemus sp.), and unidentified animals. Bait uptake by foxes was significantly higher during summer than winter (P = 0.022), and foxes accepted baits most frequently at fox dens during early summer (52.8%). Burying baits reduced bait removal by species other than foxes (P < 0.01). For rabies control in urban areas, avoiding contact of nontarget species with the rabies vaccine is particularly important. Greater selection of the fox population can be achieved by distributing baits in winter, burying baits, and choosing sites that are less accessible to non-target species. However, with anthelmintic treatment, uptake by nontarget species is of lesser importance; hence, the effort to bury the bait is unnecessary.

Oral vaccination against rabies and the behavioural ecology of the red fox (Vulpes vulpes).

As a result of oral vaccination of foxes (Vulpes vulpes) against rabies, this virus disease has almost been completely eradicated from West- and Central Europe. In most countries, vaccine baits were distributed twice a year: during spring (March to May) and autumn (September to October). This strategy has shown to be able to control and eventually eradicate rabies. However, it remains to be clarified if this is the most cost-effective strategy. Astonishingly, the behavioural ecology of the target species, the red fox, did receive only limited attention selecting the periods when baits should be distributed. Considering the behavioural ecology and rabies epidemiology of foxes, territory owners seem to play a key role in the spread and maintenance of rabies. Thus, oral vaccination campaigns should be targeted primarily at these animals. It is suggested that the optimal timing for bait distribution in Europe is late autumn (November) or early winter (December), depending on the prevailing climatic conditions. Additional campaigns, when financially feasible, can be implemented in order to maintain a high vaccination coverage during the remaining year. Furthermore, different baiting strategies can be selected in case of re-infection or persistent residual foci.

Effect of the timing of applications and amount of 0.01% diphacinone consumed on mortality of California ground squirrels ( Spermophilus beecheyi)

Diphacinone, a first-generation anticoagulant rodenticide is used extensively for control of California ground squirrels ( Spermophilus beecheyi). The potential for secondary poisoning hazards, has necessitated development of baiting strategies that minimize the amount of bait applied, while still providing a high level of control. Laboratory studies conducted to determine the effect of the amount of bait, number, and timing of 0.01% diphacinone bait applications on mortality rate of California ground squirrels suggest that only 2 applications with 3–5 d between applications are necessary to achieve control. This is contrary to previous beliefs that there must be no more than 48 h between feedings. Reducing the amount of bait per application by 71% had no significant effect on mortality rate.

Reintroduction of the burrowing bettong Bettongia lesueur (Marsupialia: Potoroidae) to mainland Australia

The burrowing bettong was successfully reintroduced to the Australian mainland in 1992 after an absence of 50 years. The population, derived from 42 individuals translocated from a remnant population on an offshore island, has persisted for over seven years on the Heirisson Prong peninsula at Shark Bay in Western Australia. It has grown to over 260 individuals that are distributed widely through available habitat. The successful management of exotic European foxes and feral cats proved crucial to the outcome of the reintroduction. Factors contributing to the successful management of predators and to a reduction in their impact included: the choice of a narrow peninsula as the site for reintroduction (permitting cost-effective use of predator-proof fencing); effective baiting (fox and cat) and trapping (cat) strategies; the maintenance of an in situ breeding colony (to provide insurance against major loss of free-range animals to predators); choice of high quality habitat (providing reasonable cover and promoting a high and relatively stable rate of increase for bettongs, even during dry years), and choice of a site that was accessible for regular management visits. An abundance of European rabbits at the reintroduction site appeared not to be a limiting factor. The success of this reintroduction has stimulated a range of other reintroductions of endangered mammals to arid and semi-arid sites across Australia, particularly to peninsulas or other sites where exotic predators can be controlled effectively.

Towards ecologically based baiting strategies for rodents in agricultural systems

Rodents are a major pest in Australian agricultural systems where they periodically irrupt (outbreak) and cause serious damage to crops. These irruptions still occur despite extensive baiting campaigns. Most of the economic losses caused by rodents occur in cereal and oilseed crops, although significant damage occurs annually in both sugar cane and macadamia orchards. Currently, attempts to control rodent outbreaks rely heavily upon baiting with rodenticides. As these are normally applied in an emergency situation and without adequate scientific insight or planning, they are usually not cost effective. We present strategies aimed at reducing agricultural losses in the event of an outbreak that take into consideration important population processes such as: (a) the stage of development of the rodent population; (b) the likely course of population trends given prevailing environmental conditions; (c) the spatial relationship between the available habitat types; (d) the role of refuge areas in seeding adjacent areas and sustaining a high population in the absence of a crop habitat type; (e) the likely dispersal strategy of the population given the landscape of the area; (f) the consequences of dispersal into areas that do not yet sustain a high population, and for crops that will be harvested late in the season. A process, presented in the form of a flow diagram, has been developed to tailor rodent control programs to specific outbreak conditions. Initially, the extent of a reported rodent problem and the scope of a control program are determined. Where a control program is required, this is developed for each region individually and is based on results of extensive population and crop surveys. Bait application rates are specifically determined for each rodent outbreak, reducing the probability of under- or over-baiting. Two baiting strategies have been developed for inclusion into the control program, a protection strategy and a control strategy. The former is designed to frustrate responsive dispersal into crops at harvest, whilst the latter will reduce numbers and maintain them at a low level until harvest. The procedure is reiterated for as long as the problem persists allowing control procedures to be modified as population and crop changes occur. Using Australian examples to illustrate the ecological concepts underpinning rodent management in an emergency situation, the control processes outlined will have universal application in the management of rodent outbreaks in agricultural systems.

Reduced risk anticoagulant baiting strategies for California ground squirrels

Author(s): Whisson, Desley A.; Gorenzel, W. Paul; Salmon, Terrell P. | Abstract: The anticoagulants diphacinone and chlorophacinone (0.01% and 0.005% concentrations) are used extensively for control of California ground squirrels (Spermophilus beecheyi). Because of concerns of risks to nontarget wildlife, there is a need to develop baiting strategies that minimize the amount of bait applied, while still providing a high level of control. In 1997 and 1998, we conducted laboratory studies to determine the effect of timing and number of bait applications, and amount of bait given per application on the efficacy of 0.01% diphacinone for California ground squirrels. Results suggest that only two applications with 4 or 5 d between applications are necessary to achieve control. This is in contrast to the label recommendation of three to four applications with 48 h between applications (spot baiting), and two applications with 2 or 3 d between them (mechanical broadcast baiting). Furthermore, in our study, squirrels only required a small amount (less than 4 g of bait) per application to receive a lethal dose. Field studies are underway to test this baiting strategy and various bait application methods in the field.

The effectiveness of a large-scale baiting campaign and an evaluation of a buffer zone strategy for fox control

The effectiveness of a baiting campaign against red foxes (Vulpes vulpes) was investigated in a rangeland area near Carnarvon, Western Australia. An area of 3180 km2 was aerially baited with dried meat baits containing 3 mg 1080 poison (5 baits km–2) in August 1995. All 45 radio-collared foxes monitored in the area were killed by baits. More than half the radio-collared foxes died within 3 days of baits being laid; the last surviving radio-collared fox died 44 days after baits were laid. The overall population reduction was estimated to be &gt;95%. Further implications of this high level of bait uptake are discussed in relation to immunocontraceptive control of foxes, as well as for population reduction or vaccination of foxes to control rabies. Reinvasion of the baited area occurred mainly in autumn, when juvenile foxes were dispersing. The relevance of this result is discussed in relation to developing more effective baiting strategies. As part of another experiment, outer sections of the baited area were periodically re-baited as a buffer zone to reduce immigration by foxes into the central baited area; the buffer baiting proved to be very effective in preventing recolonisation of the entire baited area.

Coprophagy Facilitates Horizontal Transmission of Bait Among Cockroaches (Dictyoptera: Blattellidae)

Baits offer several advantages over other insecticide formulations in the control of populations of the German cockroach, Blattella germanica (L.). However, they may fail to target certain life stages that feed only sparingly. Recently we have demonstrated that 1st instars are significantly more vulnerable to insecticidal baits when adults are present. By preventing adults or nymphs from eating bait we now conclude that adults translocate insecticide bait to the shelter, thus facilitating a horizontal transfer of the insecticide to nymphs. By tracking bait movement with a tracer dye, we show that nymphs take up adult-delivered bait via coprophagy. An alternative hypothesis, that adults delivered novel food odors to nymphs thereby stimulating them to forage and eat bait, was experimentally rejected. Analysis of time-lapse video records showed that 1st instars foraged sparingly compared with 2nd instars and adults, indicating that direct ingestion of a remotely placed bait accounted for little, if any, mortality in 1st instars. The magnitude of coprophagy in 1st instars was related to the proximity of the food to their aggregation site; nymphs ate significantly more adult feces when food was far from the shelter. We conclude that aggregating 1st instars are relatively sedentary, and that they depend on conspecific foragers to deliver widely dispersed food. Innovative baiting strategies should therefore maximize forager-mediated translocation and delivery of slow-acting bait insecticides to inaccessible cockroach aggregations.

Hoop Traps as a Means to Capture Burbot

Abstract From 1985 through 1987, the efficacy of baited, rigid hoop traps for catching burbot Lota lota was tested in several lakes and the Tanana River in central Alaska. Experiments were conducted on the diurnal catchability of burbot, optimal baiting strategies, retention of burbot, optimal duration of soak, condition of captured burbot, size of hoop traps, recruitment to the gear, and capture-induced behavior of burbot. Baiting was needed to capture burbot. Once caught, burbot rarely escaped the gear. Burbot held in hoop traps set in lakes maintained their condition for days; condition of burbot held in rivers deteriorated after the first day of captivity. Rebaiting hoop traps daily improved catches in lakes, but not in the river. For once-baited sets, optimal soaks were 2 d in lakes and 1 d in the river. Hoop traps of different sizes caught burbot of similar sizes in lakes, but large traps caught slightly larger fish in the river. Burbot were fully recruited to hoop traps usually at 450 mm total leng...