Using conditioned taste aversion to reduce human-nonhuman primate conflict: A comparison of four potentially illness-inducing drugs

Abstract

Human-wildlife conflict in the form of crop- and livestock depredation is escalating worldwide and many species of nonhuman primates are considered serious crop pests throughout areas within their ranges that humans inhabit. Animals become habituated to many non-lethal mitigation strategies, which then become ineffective at reducing crop-foraging intensities by nonhuman primates, so people have turned to culling to reduce crop losses. An example of this problem is primate crop depredation in northern India, where rhesus macaques (Macaca mulatta) have been declared vermin. Conditioned Taste Aversion (CTA) develops when humans and nonhuman animals associate the taste and odor of food with post-consumption illness and results in subsequent refusal to consume the food associated with illness. The length of time that the food is avoided indicates the aversion’s strength. CTA can be induced deliberately when food is paired with a drug that causes nausea. Thus, exploiting CTA could be a non-lethal and effective method to control crop damage caused by vertebrate pests. We tested four drugs on 88 rhesus macaques to assess their ability to induce a CTA and determine safe and effective doses. Our results suggest that fenbendazole, an anthelminthic drug with a high margin of safety, is ineffective. A similar drug, levamisole also was ineffective, as the monkeys detected it during the acquisition phase. However, we were able to create aversions using thiabendazole, another anthelminthic, and 17 alpha-ethynyl estradiol (EE). Once a dose appropriate to induce a CTA was determined, EE demonstrated a success rate of 86 %, and thiabendazole 46 %. Both drugs have strengths and weaknesses. Only a small dose of EE (25 mg/kg of body weight) was required to induce a CTA, which can be concealed in a small amount of food. However, it is a synthetic hormone, so access to the drug should be limited, and its distribution in the environment controlled. Thiabendazole required a considerably higher dose (160 mg/kg of body weight) to establish a CTA and may be a greater challenge to conceal. Nonetheless, both drugs appeared to go undetected in these tests and could be used with mild baits, e.g., wheat and corn/maize. We urge continued conditioned taste aversion studies across species to reduce crop damage.