Rosemary Beetle
an Insect Pest that destroys Rosemary and Lavender Herbs
The Rosemary Beetle has arrived in England
Chrysolina americana was once restricted to southern Europe, but with global climate change it has now invaded southern England. The adult beetle and the larvae both eat the leaves of herbs. They seem to prefer Rosemary (Rosmarinus officinalis), but will also eat lavender, thyme and sage.
The Beetle
Very beautiful, just like the Colorado Beetle (Leptirsa decemlineata) – beautiful but dangerous! The Rosemary Beetle is very pretty, with his (or her) metallic purple carapace showing delicate green stripes. Small (6mm) and ‘jewel-like’, these adults sit amongst the foliage and probably do little damage. BUT – their eggs will hatch into nasty little larvae. These young ones are greyish and they have enormous appetites. They nibble away at the rosemary leaves (or lavender) and can destroy the whole plant.
Larvae
The young ones are not as attractive as the adults. They are a greyish colour with darker stripes running along their bodies. They have the endearing habit of covering themselves with their own excreta! To me this suggests that their natural enemies might well be birds - or, at least, another ‘visual predator’. Once they have finished gorging on the plant they drop into the soil to pupate. New adults emerge in the next year and carry on with the attack.
Insecticides
Once have the beetles on your plant it is too late! The larvae will have eaten most of the leaves and damaged the plant beyond repair. You might be tempted to apply insecticides liberally – but herein lies a serious problem. If you apply insecticides while there are still flowers on your rosemary (lavender) you will also kill off the natural pollinators. There might well be little noticeable effect, but ‘low-level’ insecticides can wreak havoc with insect behaviour, Bees might well become ‘stupid’ (See my blog).
Hand Picking
Perhaps the safest way to deal with the problem is to simply pick the adult beetles off the affected plants. This is easy to say – but what do you do with a pot full of these beautiful creatures? I suppose you ought to kill them! But beetles are very tough. Soapy water is often a good deterrent, and it has little ‘long-lasting’ effect. It also helps with the aggression – ‘chuck a bowl at them’. Unfortunately any surviving adults will go off to find new plants to attack.
Other Issues
The Rosemary Beetle is just one of many bugs that can affect our flower and herb gardens. When we attempt to deal with the problem we might also be adding to the much more serious problem of ‘Pollinator Decline’. The concern is that indiscriminate use of insecticides might well do more harm than good (in the long-term).
Whatever you do – think of the bees!
Refer: Royal Horticultural Society UK
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