A few months ago I noticed what appeared to be a strange ladybird on my rosemary plant, an insect I had never seen in the UK before. The creature was incredibly beautiful, a small beetle with a hard shell that was shimmering fluorescent green with red stripes down its back. Searching online, it appears that I had an infestation of rosemary beetles, an invasive species in the UK, somehow making its way from southern Europe, that has only been recorded here within the last decade and decimates rosemary, lavender and similar herbs.
Not wanting to spray any chemical control on my herbs we took to knocking the insects off by hand and stamping on them. This seemed to work for a while—there was a period of a few weeks where I didn’t see any of the creatures—but now they appear to be back with a vengeance. They’re all over my rosemary, in the lavender plant next to the rosemary, and now have made their way across my patio to a tub of newly planted herbs, appearing all over a garden mint plant.
So: it appears that picking them off by hand and stamping on them is no real way to control them. I do it every night but the waves just keep coming and coming. Is there any biological control, or chemical control safe for use in culinary herbs, that can shift them? Any other advice in dealing with this pest is appreciated; our rosemary plant is beginning to show signs of the infestation and is looking less and less healthy by the week. My garden is full of birds but they appear completely uninterested in picking the beetles off the plants (though they are pretty hard to spot) and eating them.