When the leaves have shrivelled and discoloured it could just be that the insecticide was applied to plants in direct light.
I've had the exact same thing happen when i've done this to outdoor plants.
If you spray an insecticide you must make sure that bright light doesn't touch the plant for several hours - i always apply it in the evenings now so that bright light can't damage the sprayed areas.

I grow Kohlerias on a south facing windowsill, but with quite an amount of bubble wrap blu-tacked to the pane so as to reduce the light's intensity. The amount of light the plant received when sprayed was the same as the amount it usually receives. I can't remember whether it was sunny or cloudy at the time. I will try again like you say, giving more light protection. Thanks Louise.

Also check the label on the Provado - lots of insecticides give a short list of plants they're not suitable for, but I agree they shouldn't be sprayed in sunlight. Also Jonathan, there are many insecticides out there which aren't as heavy duty as Provado, particularly non systemic ones - I know that means you have to spray more often, but better that than killing the plant with treatments.

I can also tell you that almost all insecticides kill any members of the Crassulaceae. Even Provado Vine weevil killer does Sedum and Sempervivum no good at all.

That's an interesting fact and good to know.

I will try like you say Bamboo to find some other milder kind of spray. It doesn't say on this bottle what it isn't suitable for, but does say avoid bright light. I might also try experimenting with the 'rubbing with fingertips' technique to squash aphids, but am prepared for a loss or two if some plants are damaged by. I've plenty of Kohlerias to experiment on fortunately. Many thanks.

Owdboggy, I have had no trouble spraying Crassulaceae members with carbaryl for mealybugs, but I don't know if that is available in the UK.