Abstract
Globally, introduced pest species pose significant challenges to native ecosystems and biodiversity. New Zealand has long attempted to protect biodiversity from introduced pests such as the brushtail possum (Trichosurus vulpecula). There have been small successes at the regional level, but the transition to country-level possum management brings new challenges. This thesis integrates research motivated by concerns about the impact of possums and the need to improve the effectiveness and efficiency of potential future management techniques.
A review of the literature suggested that, despite the variety of techniques used in modern pest management, New Zealand possum management is challenging. The various existing techniques (such as 1080 poisoning, trapping, and shooting) continue to be used to manage possums and other introduced pest species on mainland islands and islets, but the review also suggested that widespread, nationwide management requires alternatives to current management tools.
The results of the 2022 public perception survey, which included 537 participants, revealed that 88% of the New Zealand public identified possums as a major problem for New Zealand. However, only 34% thought that aerial 1080 was publicly accepted. Specific concerns related to the use of 1080 continue to be raised: (1) non-target species concerns (78-88%), (2) animal welfare concerns (77%), and (3) human health concerns (73%). Also, 76% of the public felt that the government agencies involved should invest more effort into possum management programmes, particularly in terms of communicating effectively with the public and finding a better alternative to managing possums in New Zealand. Interestingly, the majority (73%) supports possum-specific fertility control as an alternative for possum management that should be explored and developed in New Zealand. These results of the current work suggest that the New Zealand public sees the need for possum management that is poison-free, targeted, environmentally friendly, humane, and more socially acceptable than the techniques currently in use.
An alternative to improving the effectiveness and efficiency of potential estrogen-based oral contraceptives (fertility control) for possums was investigated by comparing the inhibitory potential of hepatic CYP3A catalytic activity and UGT2B glucuronidation in possums to that of four other species (mice, rats, avian, and humans). The study reported higher CYP3A protein levels in possum liver microsomes compared to other test species (up to a 6-fold difference). Also, possum liver microsomes had significantly higher basal p-nitrophenol glucuronidation activity than other test species (up to an 8-fold difference). These differences in protein content and activity in possums provided an opportunity to further exploit the differences in inhibitory activity of these major drug-metabolising enzymes using CYP3A substrate-based (cineole and its analogues) and potential inhibitor-based (CYP450 inhibitor-based) compounds. Cineole (up to 50 µM) and its analogues did not significantly inhibit CYP3A and UGT2B enzymes in possums and other species screened. Similarly, none of the CYP450 inhibitor-based compounds significantly decreased the catalytic activity of possum CYP3A and UGT2B below the estimated IC50 and 2-fold IC50 and thus were not considered to be potent inhibitors of these enzymes. However, some reduction (>65% of control) in p-nitrophenol glucuronidation activity by compounds such as isosilybin, ketoconazole, and fluconazole was observed in possums, which could provide opportunities for future compound screening given the structural features of these compounds. Most importantly, this study provided preliminary evidence that the basal activity and protein content of the major drug metabolising enzymes differ in possums compared to other test species, which therefore suggests that this could be further exploited to reach the ultimate goal, a potential target-specific fertility control for possums in New Zealand.