Broadcast application of a placebo rodenticide bait in a native Hawaiian forest

doi:10.1016/S0964-8305(00)00066-4

International Biodeterioration & Biodegradation

Volume 45, Issues 3–4, April–June 2000, Pages 199-208

https://doi.org/10.1016/S0964-8305(00)00066-4 Get rights and content

Abstract

This study consisted of three replicates of controlled field trials using a pelletized placebo (Ramik® Green formulated without diphacinone) bait treated with a biological marker and broadcast at three application rates — 11.25, 22.5 and 33.75 kg/ha. We determined that Polynesian (Rattus exulans) and roof rats (Rattus rattus) consumed this bait when broadcast on the ground and assessed the optimal sowage rate to result in maximum exposure of bait to the rats while minimizing bait usage. All Polynesian rats captured in all application rates had eaten the bait. The percentage of roof rats that had eaten the bait increased with application rate, however, 22.5 kg/ha was clearly the optimal application rate. Bait degradation and invertebrate activity was documented and assessed.

Introduction

Introduced rats (Rattus spp.) have had devastating impacts on insular ecosystems worldwide, including the Hawaiian Islands (Atkinson, 1977, Buckle and Fenn, 1992, Moors et al., 1992, Seto and Conant, 1996). In the Hawaiian Islands, rats have been implicated in the extinction of numerous native species directly through predation and indirectly via competition for habitat and food resources (Atkinson, 1985). The presence of commensal rats in native ecosystems has contributed significantly to declines in endemic Hawaiian flora and fauna (Atkinson, 1977, Baker and Allen, 1976, Scowcroft and Sakai, 1984, Stone, 1985, Scott et al., 1986, Hadfield et al., 1993). Introduced rats spread seeds of invasive alien plants and are (or have been) vectors for human and animal diseases such as leptosporosis and plague in important watershed habitats (Tomich, 1986).

Rodent control, therefore, is considered a high priority for many species and ecosystem restoration plans in Hawaii (Tobin, 1994). Broadcast rodenticides have been used successfully to control introduced rodents for species conservation and habitat restoration in New Zealand (Miller and Anderson, 1992) and could potentially be used in Hawaii. The apparent success of New Zealand rodent control efforts (Innes et al., 1995) prompted the formation of a multi-agency rodenticide working group in Hawaii to seek regulatory approval for the use of similar techniques in this state.

Diphacinone is an anticoagulant, which reduces clotting factors by inhibiting the vitamin K cycle (Hadler and Buckle, 1992). Diphacinone was selected as the rodenticide to pursue for registration because of its effectiveness against rats in Hawaii (Tobin, 1992), relative low risk to non-target species of concern in the natural areas where it will be used — birds (Joerman, 1998, Kaukeinen, 1982), and limited persistence in the environment (Lund, 1988). In 1995, collaborative efforts of the working group culminated in the state registration of Eaton’s All-Weather Bait Blocks rodenticide® (0.005% diphacinone) for use in bait stations to reduce rat depredation in native Hawaiian ecosystems. At present, two formulations of Eaton’s bait (fish-flavored-SLN HI 970007 and peanut butter-molasses flavored-SLN HI-940001) are approved for use in bait stations for conservation purposes in the state of Hawaii. In June 1998, Hacco Inc. also obtained a similar state registration for Ramik® Mini Bars All-Weather Rat and Mouse Killer (SLN HI-980005); a fish flavored compressed cereal grain bait containing 0.005% diphacinone.

Application of rodenticides in bait stations can be an effective technique for reducing rat populations in limited areas (Erickson and Halvorson, 1990) but is extremely labor intensive and impractical for large areas (Nelson et al., in press). There is a critical need to obtain similar registrations for a broadcast use pattern of rodenticides in Hawaiian conservation areas. Since many of the sites where native flora and fauna are threatened by predation are in remote and rugged areas with limited access, the only cost-effective method for rodent control in these sites is the broadcast application of a rodenticide bait (Tobin, 1992, Tobin, 1994). The Eaton’s and Hacco’s fish flavored diphacinone bait formulations currently approved for use in bait stations are being considered for registration for broadcast application in Hawaii.

To obtain registration for broadcast application of diphacinone bait pellets for conservation purposes; the efficacy of the product and technique on rodents in native environments must be determined. For broadcast application of diphacinone bait pellets to be effective, the bait must be applied at a sufficient density so that >80% of rats encounter and ingest a lethal quantity of bait over a successive number of days (Marsh, 1986). A series of laboratory bioassays conducted with a commercially available Ramik® Green pelletized bait containing 0.005% diphacinone (EPA Reg. No. 2393-508) determined the minimum dosage (30–37 g of bait) and exposure time (6–7 days of feeding) needed to achieve control of R. rattus and R. exulans (Swift, 1998). Our field study used these laboratory results as the basis for developing a technique for broad-scale control of rodents in Hawaiian forest ecosystems.

This study consisted of controlled field trials using placebo Ramik® Green pelletized bait (formulated without diphacinone) treated with a biological marker and broadcast at three application rates over three replicates. The objectives were to determine (1) if rodents in native Hawaiian forests consume Ramik® Green rodenticide bait that has been broadcast on the ground and (2) an optimal rate for broadcasting the bait that results in maximum exposure of the bait to the rodents; while minimizing bait usage. Mention of trade names or commercial products is for identification purposes only and does not imply endorsement by the authors or their agencies.

Section snippets

Study sites

The study was conducted in portions of forestry blocks at the Waiakea Forest Reserve near Hilo, on the Island of Hawaii. Nine forestry blocks (8–16 ha) of trees with similar stocking rates, height and crown diameters and with comparable understory and ground vegetation were selected for the installation of study grids. Grids were separated by at least 400 m to minimize movement of rodents among sites. One hectare (100 m × 100 m) grids were established at each of the nine sites, with minimal

Trapping

Sixty-three roof rats and 20 Polynesian rats were captured in the rat snap traps during 3157 trap nights from June to August 1999. Roof rats accounted for 75% of all rat captures, while 25% were Polynesian rats. Mean corrected rat trap success for roof rats was 1.8±0.3 (Table 1) and did not differ significantly between treatments (ANOVA; F=0.20; $df=2, 8$ ; P=0.83). Mean corrected rat trap success for Polynesian rats was 0.6±0.1 (Table 2) and did not differ significantly between treatments (ANOVA; F

Discussion

We recommend an application rate of 22.5 kg/ha (20 lbs/ac) to maximize bait exposure to rats, while minimizing excess bait usage. Ninety-four percent of roof rats trapped were known to have eaten the bait at this application rate. This represents a 23% increase in roof rat bait ingestion over the low application rate (11.25 kg/ha, 10 lbs/ac), with only a 2% decrease when compared to the high application rate (33.75 kg/ha, 30 lbs/ac) plots. All Polynesian rats captured in our study were found to

Acknowledgements

We thank C. Forbes, L. Oberhofer and R. Sugihara as well as numerous volunteers for help in the field. M. Fall, P. Krushelnycky, M. Laut and E. VanGelder provided helpful reviews. Funding was provided by US Fish and Wildlife Section 6 monies through the State of Hawaii’s Division of Forestry and Wildlife and the Secretariat for Conservation Biology, University of Hawaii.

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Moreover, the exposure of insectivorous birds and mammals to ARs was reported (Borst and Counotte, 2002; Dowding et al., 2006; Dowding et al., 2010) and invertebrates, including insects, snails and/or slugs, were suggested as a potential route of contamination (Spurr and Drew, 1999; Elliott et al., 2014). Indeed, a variety of invertebrates, including slugs, were observed on and around baits after the application of ARs in New Zealand, Spain or Hawaiian forests (Morgan et al., 1996; Spurr and Drew, 1999; Dunlevy et al., 2000; Elliott et al., 2014; Hernández-Moreno et al., 2013). The accumulation of ARs in invertebrates, exposed potentially by direct consumption of baits, and/or rodent carcasses and faeces and/or by ingestion of soil-bound residues, was shown in arthropods, earthworms and gastropods, including slugs (Spurr and Drew, 1999; Dunlevy et al., 2000; Craddock, 2003; Eason et al., 2002; Hernández-Moreno et al., 2013; Liu et al., 2015).
Anticoagulant rodenticides (ARs) are used worldwide to control populations of agricultural and urban rodents, but these pesticides may be accumulated in and poisoned non-target species of wildlife. Slugs may feed on rodenticide bait following field applications. Thus, it can be assumed that their predators are exposed to rodenticides through food chain transfer. However, AR exposure in the slugs has not been systematically studied. We investigated the accumulation of three ARs (chlorophacinone, bromadiolone or brodifacoum) in the slug Deroceras reticulatum exposed for a period of 5 days followed by depuration time of 4 days in the laboratory. Moreover, we studied the exposure of slugs to brodifacoum in the field. In the laboratory exposure, the slugs consumed rodenticide baits, but no mortality was observed. After 1 day, their concentrations were stable over the time and no differences were detected between the concentrations of the three ARs. After 5 days of exposure, mean concentrations in slugs were 1.71, 1.91 and 0.44 mg/kg wet weight for chlorophacinone, bromadiolone and brodifacoum respectively. A significant decrease of bromadiolone and brodifacoum in slugs was observed in the post exposure period. In the field study, brodifacoum was detected in > 90% of analyzed slugs after application of brodifacoum baits. Then, based on a toxicity-exposure ratio approach, we found that slug consumption may represent a risk of secondary poisoning for three of their predators under acute, repeated or subchronic exposure scenarios. These results suggest that the slugs are not only the potential subject to primary exposure, but also the source of secondary exposure for their predators following application of rodenticide baits.
Rodenticide incidents of exposure and adverse effects on non-raptor birds
2017, Science of the Total Environment
Interest in the adverse effects of rodenticides on birds has focused primarily on raptors. However, non-raptor birds are also poisoned (rodenticide exposure resulting in adverse effects including mortality) by rodenticides through consumption of the rodenticide bait and contaminated prey. A literature search for rodenticide incidents (evidence of exposure to a rodenticide, adverse effects, or exposure to placebo baits) involving non-raptor birds returned 641 records spanning the years 1931 to 2016. The incidents included 17 orders, 58 families, and 190 non-raptor bird species. Nineteen anticoagulant and non-anticoagulant rodenticide active ingredients were associated with the incidents. The number of incidents and species detected were compared by surveillance method. An incident was considered to have been reported through passive surveillance if it was voluntarily reported to the authorities whereas the report of an incident found through field work that was conducted with the objective of documenting adverse effects on birds was determined to be from active surveillance. More incidents were reported from passive surveillance than with active surveillance but a significantly greater number of species were detected in proportion to the number of incidents found through active surveillance than with passive surveillance (z = 7.61, p < 0.01). Results suggest that reliance on only one surveillance method can underestimate the number of incidents that have occurred and the number of species that are affected. Although rodenticides are used worldwide, incident records were found from only 15 countries. Therefore, awareness of the breadth of species diversity of non-raptor bird poisonings from rodenticides may increase incident reportings and can strengthen the predictions of harm characterized by risk assessments.
The effect of cooking on diphacinone residues related to human consumption of feral pig tissues
2011, Food and Chemical Toxicology
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However, feral pigs (Sus scrofa) range freely and are hunted as sources of food for subsistence and recreation (Giffin, 1973; Anderson and Stone, 1993) in many of the habitats where diphacinone could potentially be applied, raising the question of the potential human health hazards of diphacinone accumulation in the pig meat. Various operational management programs using bait stations continue (unpublished job progress reports, 1999, 2000, Game surveys and inventories, Hawaii Game Management Program, US Department of Agriculture, Wildlife Services, Honolulu) and there is substantial interest in the efficiencies that could be gained by using aerial baiting methods (Dunlevy et al., 2000). Rodenticide bait pellets can be very attractive to feral pigs.
We examined feral pig tissues to determine whether the potential hazard of consuming meat from pigs previously exposed to diphacinone rodenticide baits was reduced by cooking. Residue levels were measured in cooked and uncooked tissues of feral pigs exposed to sub-lethal quantities of the anticoagulant rodenticide. Pigs were provided large amounts of baits or untreated food to consume, then euthanized prior to the onset of symptoms indicative of rodenticide poisoning or sickness. For analysis, we grouped pigs into three levels of mean diphacinone consumption: 0, 3.5, and 7.4 mg/kg. None of the pigs displayed obvious signs of toxicity during the study period. The highest concentrations of diphacinone were found in liver tissue. Cooking had little effect on residual diphacinone concentrations. The hazards to humans and pets from meat from feral pigs that consumed the rodenticide diphacinone are not reduced by cooking; consumption of pig meat obtained from areas with active rodent control programs should be avoided.
Second generation anticoagulant rodenticides in predatory birds: Probabilistic characterisation of toxic liver concentrations and implications for predatory bird populations in Canada
2011, Environment International
Citation Excerpt :
Invertebrates represent another route of exposure, especially in insectivorous avian species (Dowding et al., 2006). Some potential routes of exposure to aerial insectivores include the consumption of invertebrates that previously fed on rodent faeces or carcasses and even the consumption of ground-dwelling earthworms and beetles that ingested residues or actual rodent bait (Spurr and Drew, 1999; Dunlevy et al., 2000). Clearly, given the fact that many ecosystems contain a larger proportion of insectivorous vertebrates relative to higher trophic predators, exposure could even be greater in those taxa (Dowding et al., 2010).
Second-generation anticoagulant rodenticides (SGARs) are widely used to control rodent pests but exposure and poisonings occur in non-target species, such as birds of prey. Liver residues are often analysed to detect exposure in birds found dead but their use to assess toxicity of SGARs is problematic. We analysed published data on hepatic rodenticide residues and associated symptoms of anticoagulant poisoning from 270 birds of prey using logistic regression to estimate the probability of toxicosis associated with different liver SGAR residues. We also evaluated exposure to SGARs on a national level in Canada by analysing 196 livers from great horned owls (Bubo virginianus) and red-tailed hawks (Buteo jamaicensis) found dead at locations across the country. Analysis of a broader sample of raptor species from Quebec also helped define the taxonomic breadth of contamination. Calculated probability curves suggest significant species differences in sensitivity to SGARs and significant likelihood of toxicosis below previously suggested concentrations of concern (< 0.1 mg/kg). Analysis of birds from Quebec showed that a broad range of raptor species are exposed to SGARs, indicating that generalised terrestrial food chains could be contaminated in the vicinity of the sampled areas. Of the two species for which we had samples from across Canada, great horned owls are exposed to SGARs to a greater extent than red-tailed hawks and the liver residue levels were also higher. Using our probability estimates of effect, we estimate that a minimum of 11% of the sampled great horned owl population is at risk of being directly killed by SGARs. This is the first time the potential mortality impact of SGARs on a raptor population has been estimated.
Accumulation of anticoagulant rodenticides in a non-target insectivore, the European hedgehog (Erinaceus europaeus)
2010, Environmental Pollution
Citation Excerpt :
However, invertebrates can be a route of contamination for insectivorous vertebrates (Spurr and Drew, 1999) and, although exposure of insectivorous birds has been reported (Borst and Counotte, 2002; Dowding et al., 2006), exposure of insectivorous mammals has not been studied. Potential routes of uptake by invertebrates include: the consumption of rodent faeces (Laas et al., 1985; Craddock, 2002; Eason et al., 2002); the consumption of rodent carcasses; ingestion of soil-bound residues by e.g. earthworms; and direct consumption of poison baits (Spurr and Drew, 1999; Dunlevy et al., 2000; Craddock, 2002). Given that many ecological communities typically contain larger numbers of insectivorous vertebrates relative to predators, the contamination of invertebrates potentially poses the greater risk of non-target poisoning in terms of species and individuals.
Studies on exposure of non-targets to anticoagulant rodenticides have largely focussed on predatory birds and mammals; insectivores have rarely been studied. We investigated the exposure of 120 European hedgehogs (Erinaceus europaeus) from throughout Britain to first- and second-generation anticoagulant rodenticides (FGARs and SGARs) using high performance liquid chromatography coupled with fluorescence detection (HPLC) and liquid-chromatography mass spectrometry (LCMS). The proportion of hedgehogs with liver SGAR concentrations detected by HPLC was 3–13% per compound, 23% overall. LCMS identified much higher prevalence for difenacoum and bromadiolone, mainly because of greater ability to detect low-level contamination. The overall proportion of hedgehogs with LCMS-detected residues was 57.5% (SGARs alone) and 66.7% (FGARs and SGARs combined); 27 (22.5%) hedgehogs contained >1 rodenticide. Exposure of insectivores and predators to anticoagulant rodenticides appears to be similar. The greater sensitivity of LCMS suggests that hitherto exposure of non-targets is likely to have been under-estimated using HPLC techniques.
Evaluating alternative rodenticides for island conservation: Roof rat eradication from the San Jorge Islands, Mexico
2003, Biological Conservation
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These techniques are powerful tools for preventing extinctions and they have recently been improved with the advent of new rodenticide delivery techniques, such as aerial broadcast. Using these techniques, invasive rats have been removed from over 90 islands worldwide, including most recently islands in North America (Towns and Ballantine, 1993; Donlan et al., 2000; Dunlevy et al., 2000; Taylor et al., 2000; US National Park Service, 2000; Atkinson, 2001). As the science of invasive rat eradication develops, eradication programs are being conducted on increasingly larger and more biologically complex islands (e.g. Campbell Island, New Zealand of 11,300 ha and Anacapa Island, USA of 300 ha with an endemic rodent; P. McClelland, personal communication; US National Park Service, 2000).
Introduced commensal rats (Rattus spp.) are a major contributor to the extinction and endangerment of island plants and animals. The use of the toxin brodifacoum to completely eradicate rats from islands is a powerful conservation tool. However, brodifacoum is toxic to animals other than rats and on some islands its use may not be feasible without prohibitively expensive mitigation. As part of a regional conservation program, we experimentally tested brodifacoum and two less toxic rodenticides, diphacinone and cholecalciferol, in eradicating Rattus rattus from three small islands in the northern Gulf of California, Mexico. All three rodenticides were successful in eradicating rats, suggesting that the less toxic diphacinone and cholecalciferol may be useful alternatives to brodifacoum for some island eradication programs. However, the choice of rodenticide must be balanced between efficacy and the risks to non-target species. Applied field research is needed on less toxic rodenticides, as well as improving palatability of baits. This may prove invaluable in preventing extinctions and in restoring larger and more diverse island ecosystems.

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International Biodeterioration & Biodegradation

Abstract

Introduction

Section snippets

Study sites

Trapping

Discussion

Acknowledgements

References (30)

A reassessment of factors, particularly Rattus L., that influenced the decline of endemic forest birds in Hawaiian Islands

Pac. Sci.

The spread of commensal species of Rattus to oceanic Islands and their effects on island avifauna

Studies on the endemic Hawaiian genus Hibiscadelphus (ha-kuahiwi)

The comparative rodenticidal efficiency of five anticoagulants

J. of Hygiene

Rodent control in the conservation of endangered species

Neophobia and neophilia: new object and new place reactions of three Rattus species

J. Comp. Physiol. Psych.

The decimation of endemic Hawaiian tree snails by alien predators

Am. Zool.

Forty five years of anticoagulant rodenticides — Past present and future trends

Large-scale poisoning of ship rats (Rattus rattus) in indigenous forests of the North Island, New Zealand

New Zealand J. Ecol.

A review of secondary poisoning with rodenticides

OEP/EPPO Bull.

A review of the secondary poisoning hazard potential to wildlife from the use of anticoagulant rodenticides

An evaluation of bait stations for controlling rats in sugarcane

J. Wildlf. Mang’t.

Tests indicate minimal hazard to ‘Io from diphacinone baiting

Hawaii’s Forests and Wildlife

Cited by (25)

Accumulation of anticoagulant rodenticides (chlorophacinone, bromadiolone and brodifacoum) in a non-target invertebrate, the slug, Deroceras reticulatum

Rodenticide incidents of exposure and adverse effects on non-raptor birds

The effect of cooking on diphacinone residues related to human consumption of feral pig tissues

Second generation anticoagulant rodenticides in predatory birds: Probabilistic characterisation of toxic liver concentrations and implications for predatory bird populations in Canada

Accumulation of anticoagulant rodenticides in a non-target insectivore, the European hedgehog (Erinaceus europaeus)

Evaluating alternative rodenticides for island conservation: Roof rat eradication from the San Jorge Islands, Mexico