Individual study: testing tools for eradicating the invasive toad Duttaphrynus melanostictus in Madagascar.
Abstract
In 2014, the Asian toad Duttaphrynus melanostictus was first recorded as an invasive species in Madagascar. A feasibility study identified an urgent need to test eradication tools. This study attempts to refine estimates of the toad population and test four potential eradication tools: (1) pitfall trapping and drift fencing, (2) hand-capture removal, (3) citric acid sprays, and (4) tadpole trapping. Using delimited searches and removal trials we estimate that the Asian toad population exceeds seven million post-metamorphic toads within the incursion. Pitfall trapping and drift fencing appeared to function well as control strategies, considering the challenges of operating in a rural working environment. Capture rates suggested that, at the spacing used, a minimum of 14 nights of trapping was needed to see a strong decline in capture rates. Hand-capture of toads demonstrated the potential of local labour to deplete a free ranging toad population, but also showed that the duration of effort would need to be extended as capture rates did not decline strongly over time. Citric acid spray trials showed that this topical toxicant can be very effective for toad control, especially for juveniles. Phytotoxicity trials suggest crop and vegetation damage was not prohibitive to its broader use. Tadpole traps did not work, but we are uncertain of the influence of tadpole developmental stages on this result. This study suggests that an eradication strategy may be possible and should be tested in carefully ordered trials within a delimited area. However, the prospects of employing the best methods over the entire incursion area is likely to be cost-prohibitive and extremely high risk.