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.
