Academic literature on the topic 'Bait palatability'

The palatability and efficacy of 2.5% zinc phosphide (ZP) wheat bait that had been in dry storage for about 3.5 years was tested against house mice in canola crops in the central wheatbelt region of Western Australia. Before baiting, mouse numbers in these crops were around 90 mice ha-1. Mouse numbers were reduced by 89% in the crop where the stored bait was applied at 1 kg ha-1 by aerial broadcast. The palatability of the stored bait was also determined in additional crops by comparing the amount taken with that of `fresh' ZP wheat bait. Bait (200 g) was offered in two different types of bait station: (1) in 45-cm lengths of 50-mm-diameter plastic agricultural drainage pipe, and (2) on 40-cm-diameter plastic saucers. Regardless of station type, mice often consumed significantly more of the stored product than the `fresh' bait, particularly on Day 1. This was attributed to the stored product lacking the typical, strong ZP odour that was initially present in the fresh bait. Mouse numbers on the bait station grids (1.28 ha each) were reduced by approximately 65% after 4 days of baiting. The shelf-life and palatability of ZP wheat bait seem to be relatively unaffected by prolonged storage. If any decrease in palatability occurs, then this seems to be transient and did not reduce the overall effectiveness of the stored bait.

Context Bait palatability is a key issue influencing the uptake of toxic baits or non-toxic bait markers. Animals often reject baits with high concentrations of the active compound (whether it is a toxin, vaccine or marker) because of poor palatability, thus reducing the efficacy of baiting. Foraging theory predicts that palatability will be affected not only by the taste of active ingredients in bait but also by an animal’s ability to access alternative foods. Yet few studies of bait palatability are measured in the context of an animal’s need to search and forage for other food types. Aims The present study examined whether the palatability of Rhodamine B (RB) baits for black rats (Rattus rattus) was affected when foraging constraints were placed on access to alternative food compared with when alternative food was freely accessible. Rhodamine B is a bait marker and was used as a surrogate for other active ingredients likely to be used in pest control management. Methods Each day, RB bait at one of four concentrations was provided to an individual rat along with an alternative food that was either freely available (spatially clumped with foraging constraints absent) or hidden within a matrix of tubes (spatially scattered, thus with foraging constraints present). Key results Black rats exhibited a gradient in how palatable they found RB and preferred baits that contained the lowest concentrations of RB. Importantly, RB baits were more palatable when access to alternative food was made more difficult by applying a foraging constraint. In particular, a 0.2% RB concentration appeared to represent a threshold in palatability where intake at or above this concentration was significantly affected by a rat’s ability to freely access alternative foods. The ingestion of RB dye (mg kg–1) was highest in rats that consumed the highest concentrations, even though food intake was reduced. Conclusions The consumption of baits at high RB concentrations was greatly affected by the ease of access to other foods. We suggest the willingness of the animal to consume the bait can be influenced by the effort needed to find alternative foods. Implications A higher incidence of marking in the whiskers or hair of target individuals in the field will only be achieved with the use of the most palatable concentrations of RB and environments providing low alternative food access and abundance. A trade-off between reliable marking and palatability of RB at varying concentrations must be achieved if actual bait uptake in the field is to be more accurately represented. A re-evaluation of palatability experiments may be required as access to alternative foods can have profound impacts on bait uptake.

We examined the acceptance and palatability of baits containing different contents of sodium selenite as a rodenticide, in Swiss mice under laboratory conditions. In a no-choice and choice feeding test, the animals were exposed to baits containing 0.1, 0.05, 0.025 and 0.0125% of sodium selenite. The total bait consumption by Swiss mice in the no-choice feeding test was highly negatively correlated, while total sodium selenite intake was medium-positively correlated to the sodium selenite content in the bait. In the same test, daily intakes significantly depended on the content of sodium selenite in the bait, while the exposure and associated interactions of contents of sodium selenite and exposure had no statistically significant impact. Baits with sodium selenite contents of 0.05 and 0.1% had the most lethal effects. The negative impact of the sodium selenite content on bait acceptance and palatability was confirmed in choice feeding tests. Baits containing 0.05 and 0.1% of sodium selenite displayed the biological potential to be used as a rodenticide. It is necessary to improve its insufficient acceptability and palatability by adding adequate additives to the bait. The results of this study should be verified in experiments with wild rodents.

In a free-choice experiment conducted in a series of pen trials, the influence of food preference on caching behaviour by the red fox (Vulpes vulpes) was investigated for three unpoisoned bait types: deep-fried beef liver (DFL), dried deep-fried beef liver (DDFL) and a commercial bait (Foxoff®). Although some variation in individual preferences for the DDFL and Foxoff was observed, all of the foxes in the pen trials preferred the DFL (P < 0.01) and all cached it least often (P < 0.01). Field trials then compared the uptake, consumption and incidence of caching for the most preferred (DFL) and least preferred (Foxoff) bait types. Radio-transmitters were inserted into unpoisoned Foxoff and DFL baits and a free choice of either was provided at bait stations at three independent sites. A clock module recorded the precise time that each bait was taken from the bait station. The fate of each bait (it could either be eaten, cached or remain in situ) was recorded daily and baits were replaced for five consecutive nights. There was no difference in the rate of uptake for the two baits (P > 0.05) and, despite some variation between the sites, DFL was the most often eaten (P < 0.001) and Foxoff the most often cached (P < 0.001). These data strongly suggest that a highly palatable bait will increase the likelihood of rapid consumption of baits and reduce the incidence of caching. This is likely to increase the cost-effectiveness of baiting and limit the potential for nontarget impacts due to the movement of baits. The high degree of concordance between the results of the pen and field trials suggests that pen trials can assist in the development of more effective bait types. However, conclusions about the relative efficacy of bait types drawn from the results of baiting programs that measure only bait uptake are unlikely to be reliable.

The attractiveness of two vertebrate pest-control baits (non-toxic RS5 and Pindone-impregnated AgTech) to captive skinks (Oligosoma maccanni) was assessed with timelapse video and feeding trials in New Zealand. 0. maccanni were attracted to both bait types. When dry, pindone baits were more palatable than RS5 baits. However, when wet the palatability of both baits increased and was similar. Bait size had no significant effect on palatability. Lizards ate an average of 0.01 g of RS5 bait or 0.02 g of Agtech Pindone bait, over two days. On the basis of published susceptibility data, it is unlikely that this level of consumption would expose skinks to lethal doses of these vertebrate pest toxins. Potential sublethal effects of such doses require further study.

As part of assessments of the palatability of different formulations for baits to be used for the control of feral goats, iopanoic acid and iophenoxic acid were compared as bait markers. After goats ingested iopanoic acid (25, 50 and 100 mg/kg), peak plasma iodine concentrations (4.86, 17.25 and 19.11 micro g/ml respectively) were reached after 4 to 8 h, followed by rapid excretion. In contrast, iophenoxic acid (1.5 mg/kg) was more slowly absorbed but remained stable in the plasma at concentrations greater than 2.40 micro g/ml for 3months after ingestion. When goats were fed 10 marked leaves smeared with non-toxic petrolatum containing a total of 50 mg iophenoxic acid, plasma iodine concentrations were proportionally and significantly higher than in animals fed on marked leaf smeared with non-toxic petrolatum (total of 5 mg iophenoxic acid), indicating a potential for quantifying the amount of bait ingested. Iophenoxic acid, therefore, shows the greatest potential as a bait marker for goats, particularly for quantitative use in palatability and acceptance studies.

The aim of our study was to investigate the possibility of application of essential oils as additives in cereal-based rodenticide baits, at rates which prevent mould development and are applicable in humane medicine. Also, the purpose of these oils would be to extend the utility value of baits and reduce the use of antifungal ingredients that usually affect bait acceptance. The effects of essential oils of ten different plant species, applied at rates of one and two ml per kg of plain bait, on bait acceptance and palatability in choice feeding tests for Swiss mice were studied under controlled laboratory conditions. Baits were prepared according to relevant EPPO standards (2004). The effects of essential oils on bait acceptance and palatability for Swiss mice were determined in choice feeding tests using a formula by Johnson and Prescott (1994). There was no significant statistical difference in effects between groups and sexes regarding weight change in the experiment. During the experiment and recovery period, neither change in mice behavior no deaths were observed. Cinnamon and anise essential oils, commonly used as attractants, and clove oil, were most effective because they had no negative effect on bait acceptance and palatability, while fenchel and bergamot oils showed repellent activity that grew as the oil content in baits increased.

Two longlife baits (gel and polymer) were developed by PestTech Ltd and tested on captive ferrets The palatability of both baits was significantly enhanced using natural animal extracts with extract palatability ranked in order of decreasing consumption as rabbitchicken>harerat>fish Final bait formulations (with animal extracts) ranked in order of decreasing consumption were gelpolymer>Pestofftrade; ferret paste The response of ferrets to gel bait containing diphacinone was highly variable with males significantly more susceptible than females Accordingly large doses of diphacinone will be required to kill most ferrets in the field In conclusion both gel and polymer baits were superior to Pestofftrade; ferret paste and have good potential for ferret control

SummaryRat Rattus spp. predation is widely recognised as a major threat to insular seabird populations. Rodent eradication programmes have advanced over the last two decades with purported benefits to ecosystems and seabird conservation. However, the danger of non-target poisoning to seabirds has rarely been examined, despite hundreds of insular eradication efforts. We initiated research to assess the risk of rodenticide bait to nesting Sooty Terns Sterna fuscata on Wake Atoll Complex. Placebo bait with a fluorescing dye was used in a control treatment design to track exposure and ingestion. Camera-based observations and faecal samples, post-mortem inspections and live chick observations suggested that bait exposure and consumption occurred, but that it was infrequent. Results indicated that poison bait eradication should occur outside the chick rearing phase to minimise risks to nesting seabirds. Our study also documents previously unreported environmental fluorescence, which may increase false positive results in pre-eradication assessments of bait palatability, bait uptake rates, and bait application methods that use inactive fluorescing test baits. We recommend that future conservation efforts begin with an evaluation of environmentally-based fluorescence before formal biomarker studies.

Context Introduced house mice (Mus musculus) are a serious predator of seabird chicks at Gough Island, resulting in declining populations of several threatened species. This has prompted the preparation of plans to eradicate mice from Gough and other islands. However, relatively little is known about the palatability and efficacy of rodent baits for house mice, as most studies have focussed on rats (Rattus spp.). Aims The study’s aim was to test the palatability of non-toxic forms of two commercially available rodent pellet bait formulations (Pestoff® 20R and Final®) and a new pellet bait formulated specifically for mouse control (Pestoff® 20M) to house mice on Gough Island. We also tested the efficacy of toxic Pestoff 20R and Final pellets containing 20 and 25 ppm of the anticoagulant toxin brodifacoum. Methods Five trials with 50 mice housed in individual cages and kept at ambient temperature and light cycles, were undertaken during the year. Palatability of bait pellets was measured over five days and compared with a non-toxic control food (standard ‘rodent pellets’ sourced from a pet food supplier). Toxic bait trials were run for 25 days with bait administered at 1, 2 and 10 g for a 24-h period and at 20 g per day for 72 h. Key results All three baits were highly palatable; however, mice showed the greatest preference for Pestoff 20M and 20R, consuming a larger mass of bait. Estimated oral LD50 values of brodifacoum for Gough mice were 0.44 mg kg–1 and the average time to death following exposure was 5.5 days (range 0–16 days). Two mice (~1% of those tested) survived after apparently ingesting doses of brodifacoum estimated to be 5 and 10 times the oral LD50 values, potentially indicating a lower susceptibility to brodifacoum in some individuals, although subsequent exposure at higher doses resulted in mortality. Conclusions The results of this study confirmed that house mice on Gough Island find bait pellets highly palatable and that brodifacoum is an effective toxin with LD50 values and time to death within the same range (0.4 to 0.52 mg kg–1 and 5.2 days) as other studies, indicating no major difference in the susceptibility of Gough mice to this poison. Implications We recommend that bait manufacturers produce formulations designed to be attractive to mice and consider the use of higher concentrations of brodifacoum to increase the likelihood of all mice obtaining a toxic dose when small quantities of bait are consumed, although higher toxin concentrations must be balanced against the increased risks to non-target species. Eradication operations targeting mice should undertake more than one bait drop to ensure any individuals surviving the initial drop have access to sufficient toxic bait to cause mortality upon second or subsequent exposure.

Aerial control using 1080 (sodium monofluoroacetate) baits is widely used in New Zealand for the control of introduced brushtail possums (Trichosurus vulpecula), with the aim of protecting national conservation and agricultural values from these damaging pests. This thesis integrates research, completed over 25 years, that was motivated by growing recognition in the 1970s of the extent of possum impacts and the need to improve the effectiveness and efficiency of the control operation. Field research assessed the palatability of three types of cereal-based pellet baits and carrot baits in different regions, habitat types and seasons. Palatability was assessed by the consumption of the different bait types presented independently of each other on 15-30 plots, with rotation of bait types at plots on successive nights to provide equal exposure to each bait type. There was regional variation in possums' bait preferences, possibly reflecting genotypic differences, whereas seasonal variation was less evident. Carrot bait was preferred or equally preferred to cereal bait in 14 out of 20 field trials. The proportion of possums eating baits was then investigated by, firstly, developing a technique for tracing bait acceptance using rhodamine B, a UV-fluorescent dye. In four field trials, more than 95% of possums accepted three types of dye-marked bait, eliminating bait refusal as a major reason for low kills in winter control operations. In a fifth trial, conducted in summer, only 68% of possums accepted bait suggesting that seasonal availability of favoured foods may influence bait acceptance. Since possums must encounter baits before deciding whether to eat them, field studies were undertaken to assess the coverage achieved in normal aerial baiting operations. Large gaps, up to 400 m in width, were often found between baiting swaths; these could allow some possums to survive. A controlled field experiment, using acceptance of rhodamine-dyed bait as a measure of effectiveness, showed that bait distribution was least accurate where flight paths were not marked. Where gaps of 100 m between flight paths were deliberately created, bait acceptance was slower and less than where coverage was complete. Sowing baits at 3 kg/ha was as effective as at 10 kg/ha, indicating the potential for substantially reducing operational costs by using machinery capable of faultlessly distributing baits at low rates. Navigational guidance systems were evaluated and found to improve the accuracy of bait distribution. During 1993-1997, when a lower sowing rate of 5 kg/ha was adopted operationally by regional managers, control effectiveness was unchanged but annual savings of around $9 million accrued. Because of the lack of suitable sowing machinery, a bucket was developed to permit faultless distribution of baits at lower rates, demonstrating the possibility of yet further cost-savings. The possibility of seasonal food availability affecting bait acceptance was investigated in three different forest habitats. Dyed baits were aerially distributed on 100 ha at each site in each season over two years. In each trial, fat-based condition indices of possums were calculated and the abundance of possum-preferred plant foods described. Bait acceptance was consistently high (85-100%) in the 24 trials, and was not influenced by either condition or availability of preferred foods. It seems likely that seasonal variation in operational effectiveness is caused by either the availability of sharply seasonal, scarce foods that possums may feed on intensively for brief periods, or by warmer temperatures that render 1080 less effective. The influence of 1080 on acceptance of (rhodamine-dyed) baits was investigated in a field trial. Examination of possums for dye-marking showed that 25% of possums refused to eat either a lethal quantity of bait or any bait at all, compared with 98% of possums eating non-toxic bait. This indicated that 1080 is aversive to possums, which is a potential major reason for their surviving control operations. Pen trials were therefore conducted to further examine the problem and to seek solutions. Toxic carrot baits were rejected by 27.5% of possums, equally by smell and taste aversion, whereas toxic cereal pellets were rejected by 34%, mainly by taste aversion. Orange and cinnamon were shown to be among the most preferred of 42 flavours tested and, when applied to toxic baits, 1080 was effectively masked. Bait refusal was reduced to ≤7%, the same as that recorded for possums presented with flavoured non-toxic baits. For long-term control of possum populations, aerial 1080 baiting can be used sequentially with other poisoning methods. However, the compatibility of these methods is dependent on the likelihood of possums developing bait shyness if sublethally dosed. Studies were therefore conducted to characterise and compare the four main toxicants used (1080, cyanide, cholecalciferol and brodifacoum) for induction and mitigation of bait shyness. Shyness was induced in approximately 80% of possums sublethally dosed with cyanide, 60% with 1080, 20% with cholecalciferol, and 0% with brodifacoum. Cyanide and 1080 shyness were found to persist in many possums for at least 12 and 24 months, respectively. Use of alternative bait types, and of baits containing an alternative slow-acting toxin (brodifacoum) were shown to be effective ways of overcoming shyness. This, and other related research, is reviewed to provide operational specifications that maximise the likelihood that all targeted possums will (i) encounter bait, (ii) eat it, and (iii) die. The likely future use of aerial 1080 baiting is described and the technological, economic, environmental and social constraints on its sustainability are discussed. Finally, the uptake of the research by possum managers is considered, and areas identified in the thesis where information is incomplete are summarised as prioritised topics for further research.