Evidence of pesticide resistance in medium‐sized mammalian pests: a case study with 1080 poison and Australian rabbits

Abstract

Summary1. Toxicant-resistance is a potential, or very real, problem with many pest-control programmes world-wide. However, apart from rodents, pesticide-resistance has not been well documented in vertebrates. We assessed the potential impact of developing resistance to 1080 in rabbit populations with differing levels of historical exposure to 1080-baiting programmes in south-western Australia. 2. The sensitivity to 1080 of three out of the four populations of rabbits Oryctolagus cuniculus examined had decreased significantly since Australian rabbits were last tested over 25 years ago. The lethal dose 50 (LD 50 ) values for these populations, as determined from formal toxicity trials, ranged from 0·744 to 1·019 mg pure 1080 kg − 1 , and were significantly greater ( P < 0·05) than the previously reported values for Australian rabbits (LD 50 range 0·34-0·46 mg pure 1080 kg). The LD 50 value for the fourth population (0·584 mg pure 1080 kg − 1 ), which has had the least exposure to 1080, did not differ from that reported previously ( P > 0·05). 3. The lethal dose 99 (LD 99 ) values for the four rabbit populations tested ranged from 1·181 to 1·666 mg pure 1080 kg − 1 , and suggested that, theoretically, all rabbits should be killed during routine baiting campaigns provided that there is no loss of active ingredient from the bait. In reality, the efficacy of 1080 poison bait laid in trails for controlling free-ranging rabbits was reduced in those populations where rabbits had decreased sensitivity to 1080. Mean reductions in rabbit numbers 7-9 days after trail baiting of resistant and sensitive populations ranged from 51·2% to 65·2%, and from 76·4% to 76·5%, respectively. 4. These findings suggest that genetic resistance to 1080 is developing in at least some populations of Australian rabbits. This has world-wide implications for agricultural protection and wildlife conservation programmes that rely on a 1080-baiting strategy for reducing the impact of vertebrate pests.

Reduced efficacy of baiting programs for invasive species: some mechanisms and management implications

“…2. Increasing toxin-tolerance over time has been recorded in one field study (European rabbits: Twigg et al 2002); by contrast, there have been many cases demonstrating innate and learned aversion towards baits (Table 1). Learned aversion to baits can take place after even a single bait dose, while innate avoidance responses at the population level, and the build-up of toxin-tolerance, take place over longer, evolutionary time scales, and therefore require long-term monitoring data to fully understand.…”

“…there is no cost to maintain the capacity to metabolise and excrete these compounds), in many cases these tolerances persist over 70-100 centuries after isolation from the toxic plants (Oliver et al 1977;Eisler 1995). Comparing data for controlled, formal toxicity trials, the 1080 LD 50 dose in European rabbits doubled (from 0.34-0.46 mg to 0.744-1.019 mg pure 1080 kg À1 ) over a period of 25 years for three Australian field sites that had been regularly baited since the introduction of 1080 baits in the early 1950s, with a non-significant increase in LD 50 for a fourth site that had the least exposure to 1080 baiting (Wheeler and Hart 1979;Twigg et al 2002). There was also a positive correlation between the degree of 1080-tolerance and the length of exposure to the toxin, and Twigg et al (2002) suggested that continuous ingestion of sublethal doses of 1080 was the most likely mechanism for increased toxin-tolerance.…”

“…Oliver et al (1982) 1080: e.g. Twigg et al (2002) Wild dog/dingo (Canis lupus dingo and hybrids with domestic dog C. l. familiaris) 1080: Allen et al (1996) N.D.…”

“…Understanding bait-resistance is important for the sustainable control of pests worldwide, to protect wildlife and agricultural production (Hickling et al 1999;Twigg et al 2002;Twigg 2014). In this review, we summarise what is currently known about bait-resistance (both behavioural and physiological) in vertebrate pest species of significant economic impact in Australia and New Zealand (Table 1) and provide examples of how management actions can maximise efficacy of baiting programs.…”

“…However, many pest control operations have shown significant decreases in the success of baiting over time (e.g. Quy et al 1992;Hickling et al 1999;Twigg et al 2002), due to behavioural or physiological responses in the target pest population.…”