Life Sciences Commons^™

Relative Palatability And Efficacy Of Brodifacoum-25d Conservation Rodenticide Pellets For Mouse Eradication On Midway Atoll, Peter J. Kappes, Shane R. Siers, Israel L. Leinbach, Robert T. Sugihara, Wesley J. Jolley, Jonathan H. Plissner, Elizabeth N. Flint, Kelly L. Goodale, Gregg R. Howald

USDA Wildlife Services: Staff Publications

Invasive mice (Mus spp.) can negatively impact island species and ecosystems. Because fewer island rodent eradications have been attempted for mice compared to rats (Rattus spp.), less is known about efficacy and palatability of rodenticide baits for mouse eradications. We performed a series of bait acceptance and efficacy cage trials using a standard formulation of brodifacoum-based rodenticide on wild-caught mice from Sand Island, Midway Atoll, to help inform a proposed eradication there. Mice were offered ad libitum brodifacoum pellets along with various alternative food sources, and a “no choice” treatment group received only bait pellets. Mortality in the no choice …

Factors Leading To Successful Island Rodent Eradications Following Initial Failure, Araceli Samaniego, Peter Kappes, Keith Broome, Steve Cranwell, Richard Griffiths, Grant Harper, Pete Mcclelland, Russell Palmer, Gerard Rocamora, Keith Springer, David Will, Shane Siers

USDA Wildlife Services: Staff Publications

Island rodent eradications are increasingly conducted to eliminate the negative impacts of invasive rodents. The success rate in the tropics has been lower than in temperate regions, triggering research and reviews. Environmental factors unique to the tropics (e.g., land crabs and year-round rodent breeding) have been associated with eradication failure. Operational factors have also been important, but these have not been comprehensively assessed. The environmental and operational factors using global cases where rodent eradication initially failed and subsequent attempts occurred were compared. It was determined whether operational factors explained the initial failures, whether operational improvements explained subsequent successes, and whether …

Evaluation Of A Warfarin Bait For Controlling Invasive Wild Pigs (Sus Scrofa), James C. Beasley, Lindsay M. Clontz, Allison Rakowski, Nathan P. Snow, Kurt C. Vercauteren

USDA Wildlife Services: Staff Publications

BACKGROUND: Wild pigs (Sus scrofa) cause widespread environmental and economic damage, and as a result are subjected to extensive control. Current management strategies have proven insufficient, and there is growing interest in use of toxicants to control invasive populations of this species. In 2017 a low-dose warfarin bait was federally approved for use in controlling wild pigs in the United States. However, no states have allowed use of this bait due to unanswered questions regarding welfare concerns, field efficacy, and non-target impacts.

RESULTS: All captive wild pigs fed 0.005% warfarin baits in no choice feeding trials succumbed in an average …

Relative Acceptance Of Brodifacoum Pellets And Soft Bait Sachets By Polynesian Rats (Rattus Exulans) On Wake Atoll, Peter J. Kappes, Shane R. Siers

USDA Wildlife Services: Staff Publications

Removing invasive rats from island ecosystems using rodenticides has proven conservation benefits and is an important management tool for conserving and restoring island ecosystems. However, rodenticide-based eradications can fail if not all rats consume enough bait to result in lethal toxicosis. A recent post-operational review of a failed attempt to eradicate rats from Wake Atoll suggested that some individuals may not have ingested a lethal dose of rodenticide due to potential dietary and/or sensory preferences developed via regular access to anthropogenic food sources. These food sources may be higher in fats and oils, possessing different sensory properties (e.g., softer, chewier, …

Brodifacoum Residues In Fish Three Years After An Island-Wide Rat Eradication Attempt In The Tropical Pacific, Shane R. Siers, Aaron B. Shiels, Steven F. Volker, Kristen Rex, William C. Pitt

USDA Wildlife Services: Staff Publications

Invasive rats are known to threaten natural resources and human health and safety. Island-wide rat eradication attempts have been increasing in number and scale during the past several decades, as has the frequency of eradication success. The most common method to remove all rats from an island is to broadcast anticoagulant rodenticide bait into every rat’s home range on the island. Broadcast of toxicants can put humans and other nontarget species in marine and terrestrial environments at risk of exposure. The persistence of anticoagulant residues is somewhat unknown, particularly in marine environments. Three years after ~ 18,000 kg of 25 …

A Cage Efficacy Study Of Sodium Nitrite Formulations For Rodent Control, Gary W. Witmer, Rachael Moulton, Celeste Samura

USDA Wildlife Services: Staff Publications

Rodents cause extensive damage to human and natural resources around the world. Rodenticides are heavily relied upon to reduce rodent populations and damage. However, some rodenticides are becoming less effective while others are becoming more restricted in their use. Additionally, there are growing concerns about the non-target effects of rodenticides and the humaneness of some rodenticides. In this study, we tested some formulations containing sodium nitrite, a salt that can be toxic in high enough concentrations. One of our previous studies indicated an LD50 of about 246 mg/kg for various rodent species. It was also determined that rodents could eat …

Cage Efficacy Study Of An Experimental Rodenticide Using Wild-Caught House Mice, Gary W. Witmer, Rachael Moulton, Celeste Samura

USDA Wildlife Services: Staff Publications

The availability and effectiveness of rodenticides in the US and elsewhere has been changing for various reasons. As a result, new rodenticide formulations and active ingredients are being investigated in the US and other countries. We conducted a cage efficacy study of a paste bait containing 4.4% alphachloralose. A commercial product of this nature is manufactured and used in parts of Europe. While the formulation we tested was effective (100%) in a no-choice trial with wild caught house mice, it was not effective in two-choice trials (≤ 35%). We surmise that palatability may be an issue as the mice consumed …

Assessment Of Zinc Phosphide Bait Shyness And Tools For Reducing Flavor Aversions, Katherine Horak, N. M. Hofmann, B. A. Kimball

USDA Wildlife Services: Staff Publications

Prairie voles (Microtus ochrogaster Wagner) cause extensive damage in agricultural, suburban, and urban environments. Control of these animals has historically relied on the use of anticoagulant rodenticides and zinc phosphide. However, shyness to zinc phosphide baits has reduced its efficacy. The aim of this study was to evaluate the factors involved in zinc phosphide bait shyness through preference testing. Baits were made using a rolled oat base and contained various combinations of the components of zinc phosphide baits such as lecithin, magnesium carbonate and known flavor modulators sodium cyclamate and zinc sulfate. Encapsulation of zinc phosphide was also tested …

Grass Is Not Always Greener: Rodenticide Exposure Of A Threatened Species Near Marijuana Growing Operations, Alan B. Franklin, Peter C. Carlson, Angela Rex, Jeremy T. Rockwelt, David Garza, Emily Culhane, Steven F. Volker, Robert J. Dusek, Valerie I. Shearn-Bochsler, Mourad W. Gabriel, Katherine E. Horak

USDA Wildlife Services: Staff Publications

Marijuana (Cannabis spp.) growing operations (MGO) in California have increased substantially since the mid-1990s. One environmental side-effect of MGOs is the extensive use of anticoagulant rodenticides (AR) to prevent damage to marijuana plants caused by wild rodents. In association with a long-term demographic study, we report on an observation of brodifacoum AR exposure in a threatened species, the northern spotted owl (Strix occidentalis caurina), found freshly dead within 669–1347 m of at least seven active MGOs.

Identifying Possible Alternative Rodenticide Baits To Replace Strychnine Baits For Pocket Gophers In California, Gary W. Witmer, Roger A. Baldwin, Rachael S. Moulton

USDA Wildlife Services: Staff Publications

Rodents cause substantial damage to crops in California and rodenticides have been major tools for reducing that damage. While strychnine has been heavily relied upon to control pocket gophers in California, its future availability is in question because of increased import costs. We conducted efficacy trials with captive, wild-caught Botta's pocket gophers to identify potential alternative rodenticides to strychnine. The rodenticide baits tested included three categories: acute rodenticides, first generation anticoagulant rodenticides, and combination rodenticides (containing an acute toxicant and an anticoagulant). There was a wide range of efficacies (0e100%) with these rodenticides. The first generation anticoagulants performed poorly, while …

Identifying Possible Alternative Rodenticide Baits To Replace Strychnine Baits For Pocket Gophers In California, Gary W. Witmer, Roger A. Baldwin, Rachael S. Moulton

USDA Wildlife Services: Staff Publications

Rodents cause substantial damage to crops in California and rodenticides have been major tools for reducing that damage. While strychnine has been heavily relied upon to control pocket gophers in California, its future availability is in question because of increased import costs. We conducted efficacy trials with captive, wild-caught Botta's pocket gophers to identify potential alternative rodenticides to strychnine. The rodenticide baits tested included three categories: acute rodenticides, first generation anticoagulant rodenticides, and combination rodenticides (containing an acute toxicant and an anticoagulant). There was a wide range of efficacies (0e100%) with these rodenticides. The first generation anticoagulants performed poorly, while …

Design Of A Self-Resetting, Low-Maintenance, Long-Term Bait Station For Rodent Control, Gary W. Witmer, Rachael S. Moulton

USDA Wildlife Services: Staff Publications

A low-maintenance, long-term bait station that resets itself after being triggered would be a very useful tool for controlling Richardson’s ground squirrels, or other problem rodent species, in remote locations. With collaborators, we developed and tested two such devices using lab rats in pen settings. The devices can be left in-situ for long periods of time without servicing, and requires only occasional bait and/or battery replacement. Squirrels would be unable to cache bait due to the integrated time-out mechanism. The devices use capacitive sensor or strain gauge systems for animal identification, making it very unlikely that smaller non-target species would …

Improving Invasive House Mice Control And Eradication Strategies Via More Effective Rodenticides, Gary W. Witmer, Rachael S. Moulton

USDA Wildlife Services: Staff Publications

In many cases, the control or eradication of invasive house mice has been problematic using rodenticide products that are currently registered. Our investigations using 12 commercial formulations confirmed that premise. In contrast, 11 of 12 of those commercial formulations were effective against Norway rats. Hence, we investigated 7 new rodenticide formulations to identity more effective alternative rodenticides (different formulation and/or different active ingredients). Several of the new formulations of rodenticides and new active ingredients were found to be relatively efficacious (>70% mortality) and may warrant further investigation as potential control methods for invasive house mice. Additionally, a 2-active ingredient …

An Efficacy Test Of Cholecalciferol Plus Diphacinone Rodenticide Baits For California Voles (Microtus Californicus Peale) To Replace Ineffective Chlorophacinone Baits, Gary W. Witmer, Rachael S. Moulton, Roger A. Baldwin

USDA Wildlife Services: Staff Publications

California voles cause damage to pastures and rangelands, orchards and nurseries, and a wide variety of field crops, including artichokes. The anticoagulant rodenticides (chlorophacinone and diphacinone) typically used for voles are becoming less effective in controlling their populations. Consequently, there is a need to identify new rodenticides that will have a high efficacy on California voles so that agricultural production losses to rodents can be substantially reduced. We tested a new formulation containing two active ingredients (cholecalciferol and diphacinone) as a control method for California voles. Both a pelleted bait and an oil-coated artichoke bract bait were very palatable and …

The Effects Of Vitamin K1-Rich Plant Foods On The Efficacy Of The Anticoagulant Rodenticides Chlorophacinone And Diphacinone, Used Against Montane Voles (Microtus Montanus), Gary W. Witmer, Nathan P. Snow, Rachael S. Moulton

USDA Wildlife Services: Staff Publications

Voles can cause significant losses to agriculture and wood fibre production. California growers typically rely on baits containing chlorophacinone and diphacinone to reduce vole population densities, but the efficacy of those rodenticides has been decreasing. One hypothesis suggests that voles are consuming high levels of an antidote (vitamin K1) to the anticoagulants, contained within green leafy plants. We tested that hypothesis by first feeding Montane Voles (Microtus montanus) diets that were high in vitamin K1, and then providing the animals with either: (1) chlorophacinone-containing bait, (2) diphacinone-containing bait, or (3) a control diet. We found that the chlorophacinone-containing …

Chlorophacinone Baiting For Belding’S Ground Squirrels, Craig A. Ramey, George H. Matschke, Richard M. Engeman

USDA Wildlife Services: Staff Publications

The efficacy of using 0.01% chlorophacinone on steam-rolled oat (SRO) groats applied in CA alfalfa by spot-baiting/hand baiting around burrow entrances (~11.5 g) to control free-ranging Belding's ground squirrels (Spermophilus beldingi) were compared in 6 randomly assigned square treatment units (TUs). Four TUs were given the rodenticide and 2 treated with placebo bait. Each TU was a 0.4 ha square surrounded by a similarly treated 5.5 ha square buffer zone. Baits were applied on May 13 and re-applied, on May 20 and May 22, after 7 days of un-forecasted cool wet weather greatly reduced their above ground activity. Pesticide (EPA …