Valmarg,you are possibly right about the grease catching beneficials but catches mostly include gnats and other mosquitoes, a few houseflies and once in twenty odd years a large white butterfly. i dont remember hoverflies or lacewings being caught in the grease, probably because they are not attracted into the greenhouse or polytunnel by highly coloured or scented-flower plants.
I would really like 5 to 10 others to try the grease method just to check its efficacy. It is quick and easy . Anyone out there?