Developing fertility control for rodents: a framework for researchers and practitioners

Abstract

Fertility control is often heralded as a humane and effective technique for management of overabundant wildlife, including rodents. The intention is to reduce the use of lethal and inhumane methods, increase farm productivity and food security as well as reduce disease transmission, particularly of zoonoses. We developed a framework to guide researchers and stakeholders planning to assess the effectiveness of a potential contraceptive agent for a particular species. Our guidelines describe the overarching research questions which must be sequentially addressed to ensure adequate data are collected so that a contraceptive can be registered for use in broad‐scale rodent management. The framework indicates that studies should be undertaken iteratively and, at times, in parallel, with initial research being conducted on (1) laboratory‐based captive assessments of contraceptive effects in individuals; (2) simulation of contraceptive delivery using bait markers and/or surgical sterilization of different proportions of a field‐based or enclosure population to determine how population dynamics are affected; (3) development of mathematical models which predict the outcomes of different fertility control scenarios; and (4) implementation of large‐scale, replicated trials to validate contraceptive efficacy under various management‐scale field situations. In some circumstances, fertility control may be most effective when integrated with other methods (e.g. some culling). Assessment of non‐target effects, direct and indirect, and the environmental fate of the contraceptive must also be determined. Developing fertility control for a species is a resource‐intensive commitment but will likely be less costly than the ongoing environmental and economic impacts by rodents and rodenticides in many contexts.

Rodent biology and ecologically based rodent management (EBRM)—25 years of progress through promoting multidisciplinary research

“…2022; Massei et al. 2023). Sidhu and Singla (2023) showed that the consumption of quinestrol alone for 10 days by male lesser bandicoot rats, Bandicota bengalensis , in the laboratory reduced their fertility for more than 30 days, with partial reversibility by 60 days.…”

“…From the outset, a strong understanding of the pathway to potential success is essential-the selection of the fertility control agent is simply the beginning of a long, resource-intensive, and iterative program of laboratory, enclosure, and multi-year field studies. In parallel, regulatory and governance issues as well as public acceptance must be a consistent part of the conversation (Massei et al 2023). Two papers focused more specifically on recent results assessing the effects of synthetic steroids, either a combination of synthetic estrogen (quinestrol) and progesterone (EP-1), or quinestrol alone.…”

“…In this volume, Liu et al (2023a) showed that the effects of EP-1 on the Pacific rat, Rattus exulans, were greatest in males, but that the dose and palatability of food baits containing the steroids require further development before field studies on islands would be feasible. Liu J. et al's results reflect the need to directly assess the response of a species to a control agent that has been tested in several other species (Jacoblinnert et al 2022;Massei et al 2023). Sidhu and Singla (2023) showed that the consumption of quinestrol alone for 10 days by male lesser bandicoot rats, Bandicota bengalensis, in the laboratory reduced their fertility for more than 30 days, with partial reversibility by 60 days.…”

“…In parallel, regulatory and governance issues as well as public acceptance must be a consistent part of the conversation (Massei et al. 2023). Two papers focused more specifically on recent results assessing the effects of synthetic steroids, either a combination of synthetic estrogen (quinestrol) and progesterone (EP‐1), or quinestrol alone.…”

“…The conference had eight plenary presentations, and all were of excellent quality. Five of the papers in this special issue are associated with these plenaries: Bujnoch et al 2023, Innes et al 2023, Massei et al 2023, Schramm et al 2023, and Taylor et al 2023. We will come back to these papers.…”