Paul - Almost certainly the wet weather will have had an adverse effect on many larvae and pupae that were developing over this summer. Most Lunar Underwing larvae will have been pupated by late May. Perhaps the really warm dry weather in April also had an adverse effect.  Next year we may well see a drop off in numbers of species that had small larvae in May-July this year. Interestingly I am having better numbers of Black Rustic this year and they have similar habitat preferences to Lunar Underwing.