Dear Paul,

Under natural conditions there is always a balance between the predator or
parasite and and its specific food source. If this is not the case then this
will lead to self destruction. I can not give examples from the snail world,
but there are many examples in the insect world. Most small parasitic wasps
are feeding on a single type of aphid, scale or other critter and will not
touch even the most related species. Only in such cases biological control
turns out successfull. Do not forget that in most cases the target species
is usually an introduced species, which creates havoc in a monoculture.
These target species left behind in their country of origin their natural
predators and/or parasites and are able to multiply almost unharmed. If
highly specific predators/parasites exist of a particular pest species then
they can be introduced too and successfully applied to combat the pest
species. The more locally and isolated the infestation is, the higher is the
chance of biological control. If  a rest population of the pest species will
remain in an untreated garden then an infestation of  a nearby commercial
crop may happen again and once again the specific predators/parasites have
to be introduced because all have died out in the meantime due to lack of a
suitable foodsource.
However, all this is not snail related and exists mainly in the insect
world. I do not know of any predatory snail feeding on a single type of
other snail/slug. But I know numerous examples of predators/parasites in the
insect world feeding on a single target species.
By the way these and similar items are often discussed on similar websites
as the Conch-L Net. Examples are "Pestnet" and "Aliens", both are not
dealing with molluscs but with invasive plants and animals and how to combat
them, but now-and-then also snail related stories appear on those websites.

Henk K. Mienis

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----- Original Message -----
From: Monfils, Paul <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, February 21, 2002 11:31 PM
Subject: Re: Rosy Wolf Snail Question


> <If the predator has killed  the target pest species it will
> starve soon afterwards by malnutrition.>
>
>         Hello Henk,
>
>         Is it likely that an introduced predatory species would completely
> eradicate a prey species, and then become locally extinct itself?  Isn't
it
> more likely that a permanent cyclic population dynamic would result, where
> the predator kills off most of the prey species, which causes the predator
> population to decrease, which allows the remnant prey population to
> increase, which causes the predator population to increase, etc., etc.??
>
>         Paul M.
>