On 1 Jul 2003 22:27:31 GMT, (Nick Maclaren) wrote:

In article ,
Stephen Howard wrote:

It should do. Ants 'farm' sap-sucking insects for the 'honeydew' they
excrete, and in return they offer protection against predators.
Reduce the 'minders' and you should tip the odds in favour of the
beasties that would normally prey on the black/green fly.

That is an old wive's tale.

The 'farming' ants are all tropical, and the common ants in the UK
do not even 'herd'. I have made some reasonably scientific observations
on blackfly, in my garden and elsewhere, and the evidence was that the
presence of ants makes no difference whatsoever. My observations have
been confirmed by entymologists.

I put the word 'farm' in quotes for that reason - unlike the tropical
species, ants here in the UK seem to have a less formal arrangement.

Anyone who's cast more than a cursory glance at a colony of aphids
will have noted the interaction of ants. Furthermore, anyone who's
watched ants attack prey will have noted a very distinct difference in
both their attitude and posture when tending the aphids.
If you drop a nice juicy beetle outside a busy ants nest, they won't
swiftly knock up a corral and hang about for another beetle to
increase their stock - they'll tear it apart as soon as they can
prevent it running away. In this behavioural context their relatively
benign interaction with the aphids suggests a degree of nurture -
hence the association with farming and herding.

I suspect that the relationship is quite a complex one.
For a start, adult ants themselves don't need to prey on the aphids
for proteins, but the honeydew is a valuable source of food for them.
Prey is required for the larvae though, and whilst ants will certainly
use aphids it seems rather more likely that the ants take advantage of
the fact that aphids attract much meatier prey in the form of their
own predators - the aphid colony acts as a self sustaining booby trap.

In effect, the ant acts as a middleman...or, dare I day, a pimp!

Far more ants in the UK prey on aphids than protect them in any way,
and (after several years of querying in many ways), I have failed to
discover ANY evidence that ANY ants EVER increase aphid damage in
the UK. As I mention above, quite the contrary, in fact.

Well, my own experience in my veg plot has been that if there's a
common black ant's nest ( Lasius niger? ) near the beans etc, then I
find I have more problems with aphids.
If I site the beans more to the centre of the patch ( whereby I can
more readily spot an ant nest, and take appropriate action ) the beans
seem to suffer far less problems with aphids.
Given that there appears to be no formal herding of aphids, then yes,
I wouldn't have thought that ants per se would increase the incidence
of aphid colonization - merely take advantage of it and sustain it.

There are cases where the relationship has a negative effect on the
aphid population - but this applies more to formal herding
arrangements combined with parasitic attack.

For an 'old wives tale' it seems to have a lot of credence out there
in the bio-community - and I'd be thoroughly interested in any
references you might have to work that throws a new light on this
phenomenon.

Regards,



--
Stephen Howard - Woodwind repairs & period restorations
www.shwoodwind.co.uk
Emails to: showard{whoisat}shwoodwind{dot}co{dot}uk