Scion researchers hope that the introduction of a parasitic wasp from Australia could help control a beetle which is devastating eucalypt plantations in New Zealand.
New Zealand has a long and sad legacy of introduced species, big and small, that have become significant pests. Some have arrived accidentally, whilst others were introduced for practical reasons such as food or sport.
In some cases, predators were introduced to control the herbivores whose populations were spiralling out of control – the introduction of ferrets and stoats to control rabbits, falls into this category, and it was in every respect a failure, largely because the mustelids found it much easier to eat native birds than rabbits.
Suffice to say, New Zealand now takes border biosecurity very seriously, and any attempts to deliberately introduce new species must jump through stringent bureaucratic hoops.
But it’s a process that is well worth undertaking if a new introduction could genuinely control a pest species, without any risk to valued species, a process known as biocontrol.
The concept underpinning biocontrol is the old adage that your enemy’s enemy is your friend.
The reason many introduced species spiral out of control in in New Zealand is the lack of natural pathogens or predators that keep an animal’s numbers back in check back in its homeland.
Introduce those here, and hopefully the pest population will subside, if not to extinction, at least to manageable numbers.
Scion and Manaaki Whenua Landcare Research are both involved in the evaluation and release of potential biocontrol species. It is a process that starts overseas, and when it moves to New Zealand it takes place in strict quarantine in purpose-built containment facilities.
Scion entomologist Toni Withers is just completing a multi-year process evaluating a small parasitic wasp from Tasmania - Eadya paropsidis – as a biocontrol agent for the eucalyptus tortoise beetle (Paropsis charybdis).
The eucalyptus tortoise beetle arrived accidentally in New Zealand just over a century ago. Since then it has been munching its way through eucalyptus plantations, causing serious damage.
Two previous biocontrol agents, which target the egg stage of the beetle life cycle, were introduced but have failed to make a significant dent in the beetle’s population.
Toni says that the wasp Eadya - which only targets beetles in the genus Paropsis – parasitises the larval stage of the beetle’s life cycle. A female wasp lays an egg in a larva, which becomes the home and larder for the developing pupa.
The process is reminiscent of a scene from the movie Alien.
Toni says that after 24 days, when the wasp pupa has effectively eaten most of the beetle larva’s insides, “the poor old larva starts feeling a bit worse for wear, turns a strange colour, and then within a day or two the little parasitoid grub pushes its way out.”
Toni says their research has shown that the wasps are very attuned to the eucalytus tortoise beetle larvae, and should be effective parasites.
As part of the evaluation process, Toni and her colleague Andrew Pugh have also had to investigate whether the parasitic wasp might attack native Paropsis species. It was difficult to find larvae of native species, but they eventually managed to bring one subalpine species into captivity for testing, and they are satisfied the introduction would pose a very low risk.
Scion will shortly be submitting a proposal to the Environmental Protection Authority to release Eadya paropsidis into New Zealand, and that proposal will be open for public comment. If they are given the go-ahead, Scion’s next job will be to breed up good numbers of the wasp to release into the wild.
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