Moroccan flies may beat the French for snail biocontrol

Snail biocontrol agent sought from different shores


Pests
Pointed snails aestivating on higher ground in summer. PHOTO CSIRO

Pointed snails aestivating on higher ground in summer. PHOTO CSIRO

Aa

Moroccan flies may beat the French for biocontrol of the pointed or conical snail.

Aa

Key points

Biological control of snails

  • The pointed or conical snail is one of four snail pests in Australia that causes harvest contamination
  • An international research team is investigating the potentially more effective population of the fly parasitoid already introduced as a biocontrol agent in the early 2000s

While the pointed or conical snail (Cochlicella acuta) generally does not directly damage crops, it can be a major grain contaminant that costs growers millions of dollars annually.

In Australia, it is one of four species of introduced Mediterranean land snails that cause damage to broadacre crops.

To avoid high temperatures, the snail climbs on vegetation to aestivate and is then harvested with grain.

SEE ALSO:

Few management options

With only limited on-farm management options, a biological control agent can be an important part of an integrated management approach to snails.

When pests are introduced to another country their co-evolved natural enemies, such as predators, parasites and diseases, are often left behind. Classical biological control aims at reunifying a pest with its natural enemies.

Biological control can be very successful in controlling certain pests, but the selection of a potential biocontrol agent is a serious business.

There are many important steps along the road to introduction to prevent any unintended consequences.

Thierry Thomann, of CSIRO, collecting pointed snails from France. PHOTO CSIRO

Thierry Thomann, of CSIRO, collecting pointed snails from France. PHOTO CSIRO

Surveys of natural enemies need to be completed in the native range of the pests.

Potential natural enemies are then tested for host specificity and will only be introduced to Australia if they are shown to be safe to local species.

A biological control program for pointed snail was instigated by CSIRO and the South Australian Research and Development Institute (SARDI) in the 1990s, with investment from GRDC.

Snail biocontrol

After a decade of research and specificity testing, a fly parasitoid (Sarcophaga villeneuveana - formerly S. penicillata) from France was identified as a potential biocontrol for the pointed snail.

The fly was introduced in the early 2000s on the Yorke Peninsula, in South Australia.

The fly parasitoid lays larvae on the shells of snails during summer. The fly larva enters the host snail and feeds on the inside, killing the snail in the process.

While it has established in South Australia successfully, S. villeneuveana has not proven very effective. It has spread little in the last 15 years and parasitisation levels remain low.

By seeking parasitoid flies from Morocco, rather than France, we may be able to improve the biocontrol of pointed or conical snails in Australia. - CSIRO researcher Dr Valerie Caron

Considering that fly parasitisation rates can be very high in the native range, the reason behind this low success in Australia is unclear.

Recent work using molecular tools showed that the snails in Australia are more closely related to populations in Morocco and Spain than those in France, suggesting that parasitoids from Morocco could be more effective.

A new parasitic option

To answer this question, CSIRO has teamed up with researchers from SARDI and Cadi Ayyad University, in Morocco, with GRDC investment.

To date, the CSIRO team has shown that there are different genetic populations of the S. villeneuveana fly in France and in Morocco.

At the CSIRO European Laboratory, at Montpellier in France, they are comparing the ability of fly strains from Australia, France, Morocco and Spain to control Australian snails under laboratory conditions.

Meanwhile in Morocco, PhD candidate Yassine Fendane is undertaking an intensive field and laboratory study on the effect of snail density on parasitisation rates.

The biocontrol fly, S. villeneuveana, being reared in the CSIRO laboratory in France. PHOTO CSIRO

The biocontrol fly, S. villeneuveana, being reared in the CSIRO laboratory in France. PHOTO CSIRO

A full investigation is still underway. If the Moroccan fly strain is shown to be more efficient against the snail populations in Australia - by being better adapted to Australian conditions than the French strain introduced previously - it will be imported into quarantine and tested on native Australian snail species to ensure it is safe for release in Australia.

If successful, SARDI will coordinate its introduction and potential release.

GRDC Research Code CSE00061-PYC106

More information: Dr Valerie Caron, CSIRO, 02 6218 3475, valerie.caron@csiro.au

Aa