Sacha writes
I asked Ray about the residues from sprays affecting greenhouses and
their plastic contents. He says he knows that e.g. Vapona does this
and lingers for quite some time. And the thing that kills off vine
weevil in compost but also the predators, is Suscon green. It might be
worth checking it's not in anything you use if you want to go on using
bio controls.
http://www.chemindustry.com/chemicals/069774.html

Thanks.

I think it's probably more likely to be the temperature thing - there's
certainly a correlation (even though correlation is not the same as
causation)
--
Kay