On Thu, 05 Jun 2014 08:31:22 +0100
Martin Brown wrote:

A very good rule of thumb is fast moving or with an aphid in its jaws
is a friend and slow moving or with a plant in its jaws is a foe.


Slow moving, no insect in jaws, look as though they were eating the
white stuff.

My guess would be ladybird larvae which are partial to aphids.
http://www.bing.com/images/search?q=...ae&FORM =IGRE


Saw that page yesterday, ours are smoother. No idea of scale on there,
either.

The tree has been looking sad this year, which is why we went
looking for critters.

Surprised that they can do enough damage to make a difference to
such
a vigorous tree. Hitting it with a systemic insecticide and
alternating with a knockdown and/or stiff brush with meths will
control it, but on a large tree you are unlikely to ever get rid of
it entirely.

There is, of course, no guarantee that this is causing the tree to be
unhappy, but it is a coincidence. The very wet winter may have
over-hydrated it, it is low down, and near a ditch which has been busy
this year.

Thanks for help.

--
Davey.