I live in Greece and have several Daturas growing quite happily and flower most of the year. The problem is that something is eating the leaves but I never actually see anything on them! I suspect nocturnal snails but never see any! I have sprayed with pesticide but it seems to be non-effective. Any advice please Garnet
You might have root weevils. Read about them here: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-root-weevil.htm. Another possibility is tomato hornworm which is active during daylight but hard to find due to camouflage.