Thank you all for your replies. I guess I just have to keep spraying when the crawlers are visible (which in my case seems to be throughout the year in one area of the grove or another). I recently tried to buy some metaphycus wasps, but none were available, and I have ordered some cryptolaemus beetles, which are a type of ladybird, normally used for meally bug control, but they also consume scale crawlers. I was wondering if anyone had used them, and if so, with what success? Regards, Judith Williams