Northern Territory release of the long awaited biological control agent for bellyache bush – Stomphastis thraustica
Last month, weed officers from our own Northern Territory Weed Management Branch, collaborated with biosecurity officers from both Queensland and Western Australia, to conduct field trials and release the long-awaited new biological control agent Stomphastis thraustica in the Katherine region.
The bellyache bush leaf-mining moth Stomphastis thraustica (S. thraustica) was originally thought to be a new species to science, however it has now been identified, bred and tested, and approved for release in Australia, with releases beginning in Queensland in 2022. Around the same time another insect, identical in appearance, was identified across northern Australia (Stomphastis sp.), already occurring on bellyache bush. DNA analysis demonstrated that the biological control agent released in Queensland is a separate species from the naturally occurring one and the impact it has on the invasive bellyache bush is expected to be more significant.
The task of differentiating Stomphastis species is not simple, as the existing species isalready widespread. Trials where the 2 species were forced to interbreed in captivity were successful, but it wasn’t known whether this cross-species breeding behaviour would occur in the wild. Since the new species had already been extensively released in Queensland, the Northern Territory was selected as the study site to conduct wild pheromone trials using the pheromones produced by S. thraustica females in the first few days of life, in a wild location where no S. thraustica males are present. If wild males were attracted to these females, it would indicate that the 2 species are likely to interbreed in the wild.
In June 2024, weed officers from our own Weed Management Branch collaborated with biosecurity officers from both Queensland and Western Australia to conduct these pheromone trials, where no male moths were caught, suggesting that the two species will not interbreed in a wild setting. After the trials were finalised, breeding age specimens of the new, more voracious species S. thraustica were released at several sites across the Katherine region. This opportunity was also used to deliver stakeholder information and networking opportunities for local rangers and station managers, who will be a key component of the future breeding and release of these moths.
