Publications: Research reports and publications

Trends in Vertebrate Pesticide Use and the Importance of a Research Pipeline for Mammalian Pest Control in New Zealand

7 December, 2015
Cawthron Report 2754. Prepared for Envirolink, MBIE on behalf of Northland Regional Council.


Vertebrate pesticides remain central to mammalian pest control. However, rodenticide and other vertebrate pesticide registrations have declined worldwide over the last 30 years. In New Zealand we have deliberately bucked this trend in the field of mammalian pest control with a research strategy aimed at retaining essential toxins. In parallel, a broader three-pronged strategy has evolved, accelerating the provision of improved control tools delivered in a research and development pipeline alongside methodologies and strategies for mammalian pest control. This has included seeking toxins with better safety profiles and targeted delivery systems, as well as research on biocontrol, improved traps, lures, monitoring and species recognition technology. In the field of toxins for mammalian pest control in New Zealand, two types are needed alongside traps for integrated pest management, namely acute or fast-acting poisons, and slower-acting toxins. Comparatively fast-acting compounds include sodium fluoroacetate (1080) which remains controversial and, as a result, has been extensively researched in New Zealand to enable its re-registration and has received recent favourable reviews by the New Zealand Parliamentary Commissioner for the Environment. Brodifacoum is the most widely used slow-acting rodenticide worldwide and is highly effective for controlling rodents and possums. Its tendency to bioaccumulate and cause secondary poisoning has advantages in some situations, but not when repeated control is required or where there are concerns regarding residues and food safety. Regardless of real or perceived deficiencies, these two toxins are essential for the foreseeable future for use in both ground and aerial baiting strategies, alongside research to refine their use and minimise non-target impacts.

Looking to the immediate future, as well as continuing to improve the use of existing tools, there are opportunities for further advances in wireless technology for species recognition and aiding trapping programmes, self-resetting traps and toxin delivery systems. The efficacy of these new systems will be enhanced with advanced lures and coupled with new toxins which increasingly combine ‘low-residue' characteristics with selectivity and humaneness. More selective baiting and delivery systems are needed to better enable more targeted control of possums, wallabies, mustelids, rodents, feral cats, and rabbits. Experience gained in the 1990s with the introduction of an encapsulated cyanide pellet, which kills possums swiftly without secondary poisoning, underpinned the extension in 2009 of this registration to include wallabies. Zinc phosphide has recently been researched and registered for possum control, as it carries low risk of secondary poisoning of dogs and is being registered in target-specific resetting toxin delivery systems. This should be further developed. Two red blood cell toxicants, para-aminopropiophenone (PAPP) and sodium nitrite, with a humane mode of action have been registered. PAPP is used for stoat and feral cat control; research plans include increased familiarity with its use in fresh meat baits and the development of a solid bait for ground and aerial control. Sodium nitrite was registered in 2013 for control of feral pigs and possums and its use in paste bait should suffice. Norbormide is a development showing considerable promise. It is a truly species-specific rodenticide and should be accelerated. Both norbormide and PAPP meet requirements for humaneness and specificity. Sodium nitrite meets requirements for humaneness. Diphacinone with cholecalciferol as an additive is the best option as an alternative to brodifacoum where bioaccumulation of residues and non-target effects are a concern. The use of new toxins with advantages in specific settings should be complemented by improvements in resetting trap technology, barrier approaches and novel biocontrol and genetic concepts such as Trojan females and continuing improvements in 1080 baiting and the use of brodifacoum. Resetting traps are evolving and recent innovations include improving the design of standard kill traps coupled with wireless technology to make monitoring and control along exclusion barriers without fences far more effective. This multipronged approach will facilitate the development and delivery of increasingly humane, species-targeted, low residue pesticides and alternatives to better protect endangered species and reduce disease transmission by mammalian pests.

As illustrated above, a pipeline approach for existing and new technologies has evolved, through the multidisciplinary efforts of many practitioners and research groups from several institutions in New Zealand and overseas. Skills and disciplines that have converged in the last decade include formulation, synthetic and analytical chemistry, design, mechanical and electrical engineering, toxicology, molecular biology, reproductive physiology and animal ecology, indigenous knowledge, social science and conservation and wildlife management focused on the control of small mammal pests in New Zealand. Technologies are advancing: some are new ideas at early stages, some technologies are close to proof of concept (POC), and some tools are through to registration and close to uptake by pest control professionals and community groups. Refinements in the use of 1080, conventional traps and brodifacoum have been achieved in parallel. Emergence from the new technologies research pipeline is illustrated by the example of three toxins cited above that have been through fundamental and applied research steps and registered through the Environmental Protection Agency (EPA) and Ministry for Primary Industries (MPI) for field use, namely PAPP for stoats and feral cats, microencapsulated zinc phosphide (MZP) for possums and encapsulated sodium nitrite (ESN) for both possums and feral pigs. The development of red blood cell toxins (PAPP and ESN), which are humane and lack persistence, are the first new vertebrate toxins registered for field control of mammalian pests anywhere in the world for over 30 years, and the first designed with humaneness front of mind. However, field experience and research to maximise the utility of these new tools are still lacking.

New resetting delivery systems that are under development allow for multiple pest animals, namely possums, stoats and rats (c. 200) to be killed with a single device whilst incorporating responsible toxin delivery techniques (i.e. low risk to non-targets), and these have shown promise in early pen and field trials. Further field research to complete their development and understand how best to use these resetting devices is also needed. There are still research and engineering challenges in the development of innovative features, including a ’mesh network’ to transmit data and remotely record pest interactions and new technologies identifying animal species that can be attached to toxin delivery systems to improve their safety. New ideas requiring fundamental research enter the pipeline as proven technologies emerge for uptake in control and eradication programmes or further field experience and research to optimise their utility.

Maori, and stakeholders including, regional councils, MPI, Department of Conservation and TB Free NZ have influenced research to focus on: (a) new lures and toxins that are safer, more humane, not persistent, targeted, effective and reliable, (b) better delivery methods which cost-effectively suppress pest populations or eradicate pests in perpetuity, (c) improved species identification and detection systems, (d) use of cutting-edge science to develop novel and cost-effective technology platforms for target specificity (i.e. no potential for non-target effects), non-lethal and non-GMO (genetically modified organism) control of vertebrate pests and (e) engagement to enable broad stakeholder acceptance of the tools and strategies employed.

Continued fundamental and applied research is essential to achieve endangered species protection through optimum use of existing tools and the development and uptake of promising new and improved technologies for the control of rats, stoats, feral cats and possums at this time. Anything less will cause significant delay in the application of new control and wildlife monitoring technologies and their adoption. A momentum exists with aspirations to reverse the decline of kiwi and other native species and establish predator-free status across large areas of New Zealand. This momentum needs to be accompanied by a continued focus on maintaining and improving pest control tools and strategies including new rodenticides and other exciting developments with national and global conservation export potential.

We should learn from what has happened overseas and in other fields of biosecurity activity in New Zealand where essential tools, capabilities and capacity to make advances have been lost. In summary, 1080 and other important tools have been retained; we have the ingredients for transformational change and new tools are emerging from a research and development pipeline. It is important for New Zealand’s biodiversity that this focused research continues.

Keywords: strategy, mammalian pests, control tools, research pipeline, environmental safety, native species, investment, New Zealand.