Search for parasite for Argentine stem weevil

Press, 23 December 1988, Page 22

Search for parasite for Argentine stem weevil

A New Zealand entomologist is in South America preparing the groundwork for a hunt for a tiny parasite wasp which could be used to fight Argentine stem weevil.

Dr Steve Goldson, of MAFTech at Lincoln, travelled to South America last month to establish links with South American entomologists. He is expected back in New Zealand in mid-Janu-ary.

New Zealand scientists are interested in importing a wasp parasite from South America to combat the Argentine stem weevil which caused enormous production losses and damage to pastures and cereal crops — estimated at $3OO to $5OO million each year.

The weevil has been in New Zealand since the early 1900 s and was probably introduced by accident (in stock food) from South America. Because it has no natural enemies in New Zealand, the weevil has thrived here.

Scientists discovered some years ago that high levels of a fungal endophyte, acremonium lolli, gave ryegrass some protection from the weevil. This was balanced, however, by stock grazing on high endophyte - pasture being subject to ryegrass staggers and reduced performance. Dr Goldson said if a natural enemy of the weevil could be established, pastures would probably not need the same level of endophyte. The two could act together to reduce the weevil’s effect.

The obvious place to look for an enemy of the weevil was South America.

Contact with a Brazilian student studying for a PhD in New Zealand provided New Zealand scientists with the stimulus to consider biological control of the weevil. The weevil causes damage to cereal crops in Brazil, but is kept in check to some extent by a parasite. In conjunction with the D.5.1.R., MAFTech has

started a programme to find an appropriate natural enemy of the weevil for possible importation to New Zealand.

The most likely subject is a parasite wasp, Microctonus hyperodne, closely related to the wasp, which is performing very successfully this year as a biological control on sitona weevil. Dr Goldson said scientists wanted to bring the best possible strain of the wasp into New Zealand and one which would suit the environment. They intend searching several sites in South America for a suitable wasp.

While making initial contact with South American scientists, Dr Goldson will visit several scientific bases in Brazil, Argentina, Chile and probably Uruguay.

Hopefully, he might be able to arrange for local technicians to collect samples, of the weevils containing parasites and have them sent to New Zealand in preserved form for examination.

This would allow New Zealand scientists to learn a lot more about the parasite’s availability, reproduction and level of parasitism before the live wasps were introduced.

Weevil samples from Brazil had already shown a high level of parasitism — up to 60 per cent — which is most encouraging. The level of parasitism in New Zealand could be even higher because of the lack of natural predators of the parasite.

When the New Zealanders are satisfied they have found the parasite most appropriate for New Zealand conditions, it will undergo quarantine requirements. Dr Goldson estimated the parasite could be in New Zealand in two years, provided there were no unexpected hitches.

Thought is being given to setting up a small New Zealand base in Southern Brazil where the initial screening and quarantine work could be done.