Moth Plant Beetle Misconception Cleared Up
The potential to biologically control one of the North Island’s worst weeds took a big step forward in May when the Environmental Protection Authority (EPA) granted a new approval to release a root-feeding beetle (Freudeita cupripennis) to combat moth plant.
Moth plant beetle
“The beetle (initially misidentified as Colaspis argentinensis) first caught our attention as a possible biocontrol agent around a decade ago, but there have been difficulties getting the necessary approvals to export the beetle from Argentina and get releases underway in New Zealand,” said Quentin Paynter. This meant that the original EPA approval for this beetle, granted in 2011, lapsed. When it became apparent in 2018 that we could source the beetle from Uruguay instead, the project was back on. As these beetles were from a different population, this meant repeating the host-range testing and then reapplying for permission to release,” explained Quentin.
The Waikato Regional Council again acted as the applicant for the moth plant beetle. An unexpected number of submissions were made raising concerns that the moth plant beetle might also attack swan plant (Gomphocarpus spp.), a vital food plant for monarch butterflies. “We have tested swan plant and the other close relatives of moth plant present in New Zealand, such as native jasmine (Parsonsia spp.) and blood flower (Asclepias curassavica), and are confident that none of these plants are at risk,” Quentin said. The only other species that is susceptible is the ornamental plant tweedia (Oxypetalum caeruleum),which is in the same sub-tribe as moth plant. Following a hearing in April to examine the evidence, the EPA determined that the only plant at risk of non-target damage from the moth plant beetle is tweedia, and that the benefits of controlling moth plant substantially outweigh this. If necessary, gardeners can protect tweedia plants with insecticide.
“We are now awaiting approval from the Ministry for Primary Industries to take the beetle out of containment and we anticipate the first field releases will be made in the spring,” Quentin explained. “The moth plant beetlehas a good chance of being an effective agent, given the success of other root-feeding beetles as weed biocontrol agents, and the high mortality rates of moth plants observed during host range testing and in the field in Uruguay,” said Quentin.
A second agent being pursued is a fly (Anastrepha australis, formerly Toxotrypana australis), which can turn the contents of moth plant pods to mush. During a visit to Uruguay in February 2018, Hugh Gourlay collected a limited number of larvae. These produced adults that successfully mated in containment, although only a few adults were subsequently reared through to the next generation. A lack of pods on potted moth plants meant excised pods had to be used, which resulted in low rearing success. However, the emergence of new adults was synchronised with moth plant pod production here, which is a good sign that we will be able to successfully rear this fly in containment. We are holding off importing more flies until the potted plants are big enough to reliably produce plenty of pods.
However, last season we did some further work to assess whether the fly is likely to be sufficiently host-specific to continue with, as host-testing agents that attack pods is logistically challenging. Hugh, with the assistance of an Argentinean collaborator, Soledad Vilamill, surveyed plants closely related to moth plant in Uruguay. They managed to find Oxypetalum solanoides, O. tomentosum, and O. manchesii, and none of these were hosting the fly. A database of host records maintained by USDA researcher Dr Allen Norrbom indicates that the only other plant A. australis has been reported to attack is Morrenia odorata, a very close relative of moth plant that is absent from New Zealand. “It certainly looks like the fly could be sufficiently host specific and is definitely worth pursuing further,” added Quentin.
Finally, a rust fungus (Puccinia araujiae) approved for release in 2015 has also been held up by export permit issues. However, sourcing the rust from Uruguay is not so straightforward. In the native range the rust is attacked by a hyperparasitic fungus (Cladosporium uredinicola) and is not easy to find. Argentinian collaborator Freda Anderson (CERZOS-CONICET) has retained a culture of the rust that is free of the hyperparasite, achieved after much painstaking effort. If the rust could be collected in Uruguay it would be a massive undertaking to repeat all this work, let along the host-range testing, but this option will be explored with the project funders in the near future.
This project is funded by the National Biocontrol Collective.
CONTACT: Quentin Paynter (paynterq@landcareresearch.co.nz)