Hidcote Bug of the Month August
This Rosemary Beetle is a small psychedelic and rather pretty looking beetle that has a stripy iridescent purple and green metallic armour over its body. The rosemary beetle is a fairly recent addition to Britain, it originated in southern Europe and has been found here since the mid-1990s, possibly spreading and becoming more established as a result of climate change bringing warmer winters.
The Rosemary Beetle feeds both as an adult and a grub on the foliage and flowers of a small number of plants such as rosemary, lavender, sage and thyme. It is most active from August to April although adult beetles are present throughout the year.
They are usually found in groups on stems or feeding on the new growth of plants. The larvae are small slug like grubs which are often found on the underside of leaves. They are light grey with a horizontal dark stripe along the body.
Adult beetles are normally first seen in late spring, although they remain largely stationary on plants until later in the year.
In summer the beetles begin to mate and lay eggs on the underside of leaves, larvae will hatch in about 10 days’ time and feed on the leaves for a few weeks before dropping down to pupate below soil level. Adults may continue to mate during warmer winter periods, although that is rare.
Host plants can survive light infestations without noticeably adverse effects, but in large numbers they can be potentially destructive, so the situation should not be ignored.
Although there are chemical products that can control this pest, apart from being potentially harmful to beneficial insects, they may not prevent infestations from establishing.
We came across a small number on the lavender in the pine circle last year which we hand picked off and saw very little plant damage. This year, after a very mild winter, we have noticed a much larger number of beetles.
As we take an organic approach here to pest control, we will manage the situation by carrying out regular checks and removing beetles throughout the summer and we will continue to check for larvae over the coming months.
We will have to see what winter brings us this time and monitor the situation into next year.