A California without rodenticides: challenges for commensal rodent management in the future

Rodenticides are an essential tool in the integrated pest management of infestations of commensal rodents (Rattus norvegicus, R. rattus, and Mus musculus). With the introduction of Assembly Bill 1788, the California Ecosystems Protection Act of 2019, California is potentially facing a future with new restrictions on the use of anticoagulant rodenticides to manage commensal rodents in urban areas. Assembly Bill 1788 has been proposed specifically to protect predators from anticoagulant rodenticide poisoning and seeks to restrict the application of second-generation anticoagulant rodenticides (SGARs) for use in many urban and non-urban areas of California, USA. Exclusion and cultural practices, such as landscape management and sanitation (i.e., cleaning of property including but not limited to trash containment and removal, and drain sanitation), remain important and successful tools for managing rodent populations. However, increased exposure of wildlife to anticoagulant rodenticides has been detected California. Several animal species have been documented as having succumbed to rodenticide toxicosis. When rodents are killed by SGARs and consumed by predators, SGAR residues have been detected in the livers of predatory species. However, the effects of chronic, sublethal exposure to predators are not well understood. We discuss the current and proposed changes to rodenticide legislation in California, impacts of rodenticide to wildlife, and the potential effects of restrictions on wildlife. We discuss limitations to rodent management programs that have historically replied on the use of SGARs and the potential impacts of the proposed legislation on communities across California. We also identify research gaps that are impeding the adoption of evidence-based best management strategies for rodent control. To improve the success of commensal rodent control programs in California, more research is needed to develop effective strategies for rodent management.