The palatability of undyed carrot surface-coated with repellents, or dyed blue or green to a terrestrial macroinvertebrate

Abstract

ABSTRACTBirds are at risk of being poisoned during pest control operations not only through eating toxic baits, but potentially by preying on invertebrates that have, themselves, consumed the toxic baits. Blue baits coated with anthraquinone and/or mint-scented repellents are avoided by some bird species compared with green baits coated with cinnamon oil; however, data on invertebrate avoidance patterns have not been explored. In our first experiment, we measured consumption rates in a large invertebrate, the Auckland tree wētā (Hemideina thoracica) for carrot that had been surface-coated with three repellent formulations: anthraquinone (0.8 g kg−1) (a secondary repellent); anthraquinone (0.8 g kg−1) and pennyroyal oil (a mint-scented product which acts as a primary repellent) (0.5 g kg−1); and cinnamon oil (0.15 g kg−1) (a primary repellent), over 4 days. In a second experiment, we tested whether tree wētā preferred carrot dyed either blue or green over 2 days. Tree wētā ate similar quantities of carrot from all three of the repellent formulations tested, but consumption of all three formulations was significantly lower than the control from the third day of the experiment. Tree wētā ate less blue-dyed carrot than green-dyed carrot on both days of the second experiment, but differences were not significant (day 1, P= 0.057; day 2, P = 0.145). Our findings complement the results of previous studies on some bird species. Together they show the potential of surface-coating baits with anthraquinone and/or mint oil and dyeing them blue in pest control operations to reduce non-target avian by-kill, while not increasing the risk of secondary poisoning of insectivorous species. Our results also indicate that cinnamon oil can be used not only as a toxin mask but also as a repellent to wētā.