Pests > Pests Entities > Molluscs > Management > Platydemus manokwari, a warning, references

Pests > Pests Entities > Molluscs > Management > Platydemus manokwari, a warning, references

Pests Pests Entities Molluscs Management Platydemus manokwari, a warning, references

Platydemus manokwari

December 2003. A warning about the introduction of Platydemus manokwari for the control of the Giant African snail, Achatina fulica from Israel.

Recently requests have been posted (either on the Aliens-L or Pestnet, therefore this message to both lists) for the predatory flatworm Platydemus manokwari in order to use it in the control of the Giant African snail Achatina fulica. This predatory flatworm is a voracious and indiscrimate predator of any snail and is even listed among the 100 worst invasive species.

It is suggested that people refrain from using Platydemus manokwari in any trial of controlling Achatina fulica. Like the predatory snail, Euglandina rosea, the giant toad, Bufo marinus, and several other so-called biological controls of Giant African Snails, they damage endemic (snail) fauna, and do far more harm than good.

Those interested in the use of this predacious flatworm in a control program of the Giant African Snail would be advised to read some of the numerous articles on this subject on the Internet. Hopefully, they will be disauded from making any introduction because of the unwanted side effects.

It is strange to read that agricultural agencies working in the Pacific are still supporting the use of this flatworm in the battle against the Giant African Snail. A Newsletter of the Food and Agriculture Organization of the United Nations Sub-regional Office for the Pacific Islands (SAPA), Apia, Samoa: SAPA, 6 (3): 3 (2002), mentions flatworms as means of bio-control of the Giant African Snail. More particularly they write that Platydemus manokwari is the Bio-agent for Giant African Snail in Samoa and Vanuatu. More alarming is the note: ???It is interesting to know that Platydemus manokwari is already present in Tonga and yet there is no Giant African Snail in Tonga???, i.e. this flatworm has been introduced as a precaution. In other words, it has to stay alive by predating native snails. No wonder that everywhere in the Pacific the number of endemic land snails is dwindling rapidly.

Pest Advisory Leaflet No. 6 issued by the Plant Protection Service of the Secretariat of the Pacific Community, dealing with the Giant African Snail, carries the following under the heading ???Biological Control???: ???The carnivorous turbellarian flatworm (Platydemus manokwari) has also been recommended for biological control of the snail, and good control has been achieved in Guam, the Northern Mariana Islands and the Maldives.??? Although this statement is followed by the sentence: ???Before introducing any predators, a risk assessment and environmental impact study should be carried out???, the damage has already been done. Because a farmer, demoralized by the damage Giant African Snails are causing to his crops, will not wait for an official risk assessment, and will find a way to get hold of these flatworms in order to use them in his field.

Although much damage has already been done, all those involved with control projects of Giant African Snails, whether in the Pacific or in the Indian Ocean, should refrain from using the flatworm, Platydemus manokwari, as a bio-agent. It is important to preserve the dwindling number of endemic snails; they play a unique balance of nature in those isolated places.

The following has been sent by Dr Robert H Cowie on 12 December 2003 to the Aliens-L list with a copy to Pestnet:

I concur entirely with the message sent by Henk Mienis. Experience in the Pacific with not only this flatworm but also with introduced predatory snails is that they are an extremely serious threat to native land snail biodiversity. The Pacific island snail fauna is highly diverse and narrowly endemic (Hawaii alone has over 750 species, and all but 2-4 of these are endemic to Hawaii). Predation by species introduced as putative biocontrol agents without testing them against non-targets, has already been heavily implicated in the extinction of many land snail species on various Pacific islands.

The following readings were recomended:

Clarke, B., Murray, J., & Johnson, M.S., 1984. The extinction of endemic species by a program of biological control. Pacific Science, 38: 97-104.

Hadfield, M.G., 1986. Extinction in Hawaiian Achatinelline snails. Malacologia, 27: 67-81.

Murray, J., Murray, E., Johnson, M.S. & Clarke, B., 1988. The extinction of Partula on Moorea. Pacific Science, 42: 150-153.

Cowie, R.H., 1992. Evolution and extinction of Partulidae, endemic Pacific island land snails. Philosophical Transactions of the Royal Society of London, Series B Biological Sciences, 335: 167-191.

Hadfield, M.G., Miller, S.E. & Carwille, A.H., 1993. The decimation of endemic Hawaiian tree snails by alien predators. American Zoologist, 33: 610-622.

Civeyrel, L. & Simberloff, D., 1996. A tale of two snails: is the cure worse than the disease? Biodiversity and Conservation, 5: 1231-1252.

Cowie, R.H., 2001. Can snails ever be effective and safe biocontrol agents? International Journal of Pest Management, 47: 23-40.

Coote, T. & Loeve, E., 2003. From 61 species to five: endemic tree snails of the Society Islands fall prey to an ill-judged biological control programme. Oryx, 37: 91-96.