On 2 Jul 2003 13:31:12 GMT, (Nick Maclaren) wrote:


In article ,
Stephen Howard writes:
|


| 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!

I have never seen that, and have some difficulty in believing that
it is true of Lasius niger.

L.niger is, as popular parlance might put it, 'known for it, Guv'.
In areas where L.niger actively cultivates an aphid population well
over a dozen species of aphid have been found in a nest.
Naturally, their behaviour in Britain may be modified to suit the
climate, but the species has a strong herding tendency.

Their behaviour is quite distinct from Myrmica rubra, which is common
in these parts ( a fact of which I am often painfully reminded ).
Their colonies are much smaller, and the ant is rather more
aggressive. Although I have often seen them in association with aphids
I haven't as yet observed anything but the most passing of
relationships.

Which brings me to ask.. which species were you studying, and was it
the same one across the various plots?
The point also arises that one species of ant in competition with
another for the same resources may well find it advantageous to scale
up any semi-symbiotic relationships.

| 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.

I think that can tell you why that happens, and it is almost certainly
NOT due to the ants! Blackfly overwinter on other plants, such as
Viburnum and Philadelphus. They then breed asexually, develop
winged females, fly to summer hosts like broad beans and nasturtiums
and then breed asexually like mad.

It is probably because the flying females will alight on the outside
plants first.

On my veg patch that wouldn't be the case.
The beans, and occasionally the peas, are the only things I grow that
seem to be prone to aphid attack - the salad crops I keep under
fleece.
Given that the beans are the tallest standing crop in the patch I
would think it likely that they'd be colonized wherever they were
situated in the plot - and as any cyclist will tell you, aphids can
fly quite high enough to get over most obstacles!

I certainly agree that ants, at least in this country, aren't
responsible for aphid infestations - but I'm sufficiently convinced
through observation that their presence adds to the success of an
aphid infestation.

I have been trying to control blackfly on beans by spraying infestations
on OTHER plants (mainly those two) as the beans grow, and it seems to
work.

I don't use sprays - but I find a casual stroll around the grounds and
a spot of nifty finger work keeps the little buggers under control.
It's certainly a more effective means of control than trying to
eradicate the ants.

| 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.

I haven't seen that, either, and have done a test or two.

| 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.

I have no references, but have found no references to ANY evidence
that ants increase the infestations either. Not one. And I have
done a fair amount of enquiring.

I quite agree with regard to increasing the infestation - if there's a
relationship it's an opportunistic one.

Observation of ants fighting ladybird larvae (even if correctly
deduced) merely demonstrate that they can conflict. I have seen
Lasius niger climbing over ladybird larvae to milk aphids, and
neither interfering with each other.

I've noted that too. I've also noted that ants are sometimes reluctant
to attack prime prey ( observations, it has to be admitted, that were
gleaned many years ago by collecting suitably fierce looking bugs and
popping them bang outside an ants nest ).
I assume much of this is to do with what the "ant orders for the day"
are, and the perceived threat.

With regards to your observations, what percentage of them were
carried out at night?

I have observed the difference between aphid infestations with
ants and without, in the same row of broad beans and in more than
one location, and could see no difference in their vigour or
progress.

I've not been able to test that assertion - wherever I've had aphid
infestation on crops in close proximity I've noted either the presence
of ants, or none at all. I've not been sufficiently motivated to leave
the buggers to get on with it in the interests of analysis - though I
might pop in a stand of lupins next year to assess this phenomenon.
My lad's at that age where that sort of thing ought to prove
fascinating.

I have observed the pattern of aphid infestations in many places,
and have never seen any evidence of movement by ants. In all
cases, the colonies were probably due to flying females or rain
wash. The patterns are different in all three cases.

That is why I say that it is an old wive's tale. Like many such,
it has a lot of credence and some plausible arguments, but little
evidence.

On the issue of aphid placement, yes, I'd go along with that.
On the issue of sustainment of aphid colonies, I'd say it bears more
examination. In the meantime I'll trust to my observations and knock
back both the ants and the aphids on the veg patch.

Regards,



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