Diphacinone and cholecaliciferol (D+C) as a potent low-residue rodenticide

Rodenticides such as brodifacoum are more potent than first-generation anticoagulants. However, their field, farm, and outdoor use in urban settings have been linked to bioaccumulation and non-target impacts for more than three decades. Product development strategies focused on baits that yield good control of pests without residue risks to wildlife are few. To fill this gap, a bait containing a combination of diphacinone at 0.005% and cholecalciferol at 0.06% (D+C bait) has been developed as a multispecies bait for NZ use, that is effective at killing rodents and also possums (Trichosurus vulpecula), which are resistant to the toxin effects of first-generation anticoagulants. This bait was approved by the NZ Environmental Protection Agency and the product registered by the NZ Ministry of Primary Industries in 2019. A new bait is being considered with a lower dose of cholecalciferol. A bait containing half or a quarter of the loading concentration of cholecalciferol would have an even better safety profile for rodent control alone. Cage trials indicate that cholecalciferol at 0.03% with diphacinone 0.005% is as effective as brodifacoum as a single exposure bait. Amounts of cholecalciferol as low as 0.015% significantly improve the effectiveness of diphacinone

Toxicology and ecotoxicology of para-aminopropiophenone (PAPP) – a new predator control tool for stoats and feral cats in New Zealand

Para-aminopropiophenone (PAPP) paste was approved as a stoat control agent in New Zealand by the Environmental Protection Authority in August 2011 and for feral cat control in November 2011. PAPP was originally researched in Europe and the USA as treatment for cyanide and radiation poisoning. Over the last 10 years, our research has focused on several factors, including determining its toxicity to predators, field effectiveness for controlling stoats and feral cats, animal welfare profile, toxicology, ecotoxicology, and understanding and reducing non-target risks. PAPP has been developed specifically for the control of stoats and feral cats because of the special sensitivity displayed by these species. Its toxicity is mediated by the induction of methaemoglobinaemia (the ferric state of haemoglobin). Normally, methaemoglobin levels in the blood are below 1%. Levels of methaemoglobin in the blood above 70% are usually fatal, creating a lethal deficit of oxygen in cardiac muscle and the brain. In stoats and feral cats, death after a lethal dose usually occurs within 2 h after eating bait, with clinical signs first appearing in 10 to 20 min for stoats and at around 35 min for cats. Animals become lethargic and sleepy before they die, hence PAPP is relatively humane. A simple antidote exists, namely methylene blue. Further, birds display a lack of toxicity to PAPP when compared with other vertebrate pesticides. A paste containing 40% PAPP has been developed for use in meat baits in New Zealand. A toxic dose for stoats and feral cats is achieved when pea-sized amounts of paste are delivered in 10–20 g meat baits. When meat baits containing PAPP are applied in bait stations in field settings, stoat and feral cat numbers can be rapidly reduced. However, there has been limited practical experience with PAPP to date, especially when compared with alternative tools such as traps or sodium monofluoroacetate (1080) baits. Additional practical experience should enable the effective use of PAPP as a tool to help protect native species from introduced predators. In the future, PAPP will be developed in long-life bait and in a resetting toxin delivery system

Continuing field efficacy of norbormide against both Rattus rattus (ship rats) and Rattus norvegicus (Norway rats)

Norbormide is a uniquely selective rat toxicant for Rattus species, with rats being 100- to 150-fold more sensitive to norbormide toxicity than most other mammals and birds. Previously we reported that on completion of a 10-year program of targeted fundamental and applied synthetic chemistry and toxicology, taste aversion associated with this compound had been overcome. In 2020-2022, trials have been successfully completed on poultry farms with Norway rats and larger scale field trials were undertaken targeting ship rats using 1% norbormide paste baits. Firstly, the efficacy of norbormide-containing paste baits targeting rat infestations on poultry farms was proven with a 100% reduction of Norway rat populations on three different farms. Secondly, 100% reduction in ship rat abundance was achieved at two large field test sites; and no reduction was achieved at the untreated control site. These larger field trials are described in depth in this publication. Plans are progressing to complete product development and registration

Developing a new resetting tool for controlling rats

A resetting toxin device (the “Spitfire”) has been designed that delivers a toxic paste to a rat’s ventral surface when it passes through a tunnel. The rat grooms off the paste and ingests the toxin. The system was assessed in cage trials and one field trial. The purpose of the cage trials was to investigate whether a range of toxins can be delivered by the Spitfire to rats (Rattus rattus and R. norvegicus), namely 0.55% sodium fluoroacetate (1080), 0.2% brodifacoum, 15% cholecalciferol, and 12.5% zinc phosphide. The trials with 1080, brodifacoum, and zinc phosphide were successful with > 85% of rats ingesting lethal doses. The trials with cholecalciferol were less successful with only 58% of rats dying. A one-month pilot field trial was undertaken using 1080 in the Spitfires. There was a knockdown in rat (and stoat Mustela erminea) abundance, establishing proof of concept for the Spitfire delivery system with this toxin. The long-term, effective control of introduced rats will require a range of toxins with different modes of action. The Spitfire could be a useful additional control tool for rats and is currently being re-engineered to be made more reliable

Diphacinone and coumatetralyl persistence in deer and implications for wildlife management

Eason, C.T., Murphy, E., Ross, J.G., Hix, S., Arthur, D., MacMorran, D., Broome, K., Fairweather, A

Integrating ecology and technology to create innovative pest control devices

Blackie, H., MacMorran, D., Shapiro, L., Woodhead, I., Diegel, O., Murphy, E., Eason, C.T

Retrieving and retaining older and advancing novel rodenticides-as alternatives to anticoagulants

Eason, C.T., Henderson, R., Murphy, E., Shapiro, L., MacMorran, D., Blackie, H., Brimble, M., Conole, D., Rennison, D., Gibson, T.J., Gregory N.G

Encapsulated sodium nitrite as a new toxicant for possum control in New Zealand

Sodium nitrite (NaNO₂), a commonly used food preservative, has been researched in New Zealand for the control of brushtail possums (Trichosurus vulpecula). In sufficiently high doses, NaNO₂ is toxic because it disrupts circulatory transport of oxygen. As NaNO₂ is very bitter, encapsulation and mixing it through a highly palatable bait formulation is necessary to effectively deliver it to target pest species. In no-choice cage trials, 12/12 possums consumed a lethal dose of toxic paste bait and died on average after 95.6 minutes (±4.9 SE). In two-choice cage trials 7/8 possums consumed a lethal dose of toxic paste bait and died on average after 96.7 minutes (±11.4 SE). Two field trials targeting possums using this toxic paste in bait stations reduced their abundance by 81.2% (± 2.5% SE) and 72.7% (± 1.6% SE) respectively. NaNO₂ paste, known as BaitRite, has been registered in New Zealand as a vertebrate toxic agent for controlling possums

The development of a light-weight, long-life diphacinone rodent bait

Ross, J.G., Eason, C.T., Sam, S., Shapiro, L., Blackie, H., MacMorran, D., Aylett, P., Tucker, N., Razzaq, H

Control and eradication of feral cats: field trials of a new toxin

Feral cats (Felis catus) have caused the decline and extinction of threatened species on islands worldwide. The eradication or long-term control of cats is therefore an essential part of restoring native communities on these islands. In most situations, a combination of lethal techniques is required to remove feral cats, including trapping, hunting and poisoning. Para-aminopropiophenone (PAPP) is being developed as a new, humane poison for feral cats. Mammalian carnivore species appear more susceptible to PAPP than birds, so it potentially has higher target selectivity than other available toxins. A proprietary formulation of PAPP (PredaSTOP) developed by Connovation NZ Ltd. has been shown to kill cats humanely when delivered in a meat bait in pen trials. Two field trials of the formulation were undertaken with radio-collared cats. Toxic baiting was carried out by placing meat baits containing 80 mg PAPP in bait stations. Five of eight radio-collared cats in the South Island study and 13 of 16 radio-collared cats in the North Island study were poisoned. In the latter study, an additional three cats without collars that were monitored using infra-red cameras were also poisoned. Our results indicate that PAPP is an effective toxin for cats in the field, with potential application for their eradication or control on islands