However, there remains the dilemma of what to use. I've never had cause to spray for insect attack before, only the occasional dose of Bordeaux on scab-susceptible varieties.
Derris is the only insecticide recommended by the Soil Association. The active ingredient is Rotenone. However, all rotenone-based insecticides were banned for public use last year, presumably due to the suspicion they might cause nervous system damage.
The only other choice are Bifenthrin-based inseciticides (Bug Clear), a pyrethroid compound which is also a neurotoxin. Just because such insecticides derive from plant-based substances does not make them any safer, ethical or 'natural'. Bifrenthrin isn't terribly water-soluble. Hopefully that means it won't leach straight into the water table. However, it means it's more likely it will persist in the environment.
In the end I did spray only the Conference/Concorde cordons with Bifenthrin/Bug Clear this morning. We have no Blue tits nesting this year, may be they had kept the infestations at bay in previous years, and my fear is a explosion in the population if the pest goes unchecked in this season. Hopefully this will redress the balance, and the birds will be back next year. The fact we've also had a really bad attack of Gooseberry sawfly for the first time in the last decade suggests there is some change in the pest/predator balance this year.
I'm not going to rant about 'elf and safety gorn mad. We don't know what the effects of these substances are in the environment because ecosystems are enormously complex and difficult to study. Years ago, arsenate of lead and nicotine were popular and highly effective insecticides. On the other hand, pests can destroy whole crops and commercial growers will all spray regularly as a preventative measure so the fruit-eater doesn't escape the issues either way.