I can’t help finding these little critturs visually appealing – they remind me of a Regency dandy in a stripey waistcoat of green and purple. If Rupert Everett were a beetle then this would be him.
But there my love for them ends. Chrysolina americana or Rosemary Beetle have been causing havoc in the UK since the early 1990s when they were first sighted, going on to become widespread throughout the UK as far as Scotland and Northern Ireland. They are native to Europe.
As their common name suggests they feed on rosemary but will also eat sage, lavender, thyme and perovskia, and can completely strip plants of leaves, eventually causing them to die off. They feed, mate and lay eggs from late August and September and, if the winter is mild, will continue to do so until Spring. The eggs hatch in two weeks, and the larvae will then feed for three weeks on the host plant and then enter the soil to pupate, the pupal stage lasting a futher three weeks, after which the adult beetle will emerge and start the cycle all over again.
Pest Control – I don’t advocate using pesticides if you can help it. They can be controlled to a degree by removing them by hand (if squashed they give off quite a nice perfume of whatever plant they are feeding on – not for the faint-hearted as it is quite messy..). You can shake or tap the branches of the shrub on to newspaper to remove larvae and beetles, and then dispose of them. As the beetles are unable to fly they are relatively easy to pick off. The larvae hide on the underside of the leaves.
If you have to use pesticides please don’t use them whilst the plants are in flower as this endangers bees.