Research
Rosemary leaf beetle
Introduction and description
The rosemary beetle (Chrysolina americana) is an attractive 8mm long metallic green beetle with purple stripes. Despite its scientific name, it is a native of southern Europe. During the last decade it has become an established pest in Britain on rosemary and lavender
The grubs are greyish white with five darker longitudinal lines; fully grown larvae are 5-8mm long. The 2mm long sausage-shaped eggs are laid on the underside of the leaves.
Distribution in Britain
The rosemary beetle was first seen living out of doors in the UK at RHS Garden Wisley, Surrey, in 1994 but this population died out and it was not seen again at Wisley until 2003. By 1998 established colonies of the beetle had been reported by entomologists from other sites in south east England, including near London’s Waterloo Station and Winnersh near Reading, Berkshire. In 1999 the first enquiry concerning this beetle was received by the RHS Members’ Advisory Service, from near Weybridge, Surrey. By the end of 2005 the beetle had become widespread throughout London and surrounding areas, and had become a top 10 most frequent pest enquiry to the RHS Members’ Advisory Service. Outside of the south east, the beetle is established in Norwich and specimens have been found in other areas of the including Edinburgh, Pembrokeshire and southeast Yorkshire. For a map click here
Life cycle
Preliminary research at the Entomology laboratory at Wisley Garden indicated that rosemary beetle adults remain inactive on their host plants during the summer months (June to August). In late August and September the beetles resume feeding, mate and begin to lay eggs, which they continue to do on warm winter days until spring. The eggs hatch within two weeks and the larvae feed for approximately three weeks before entering the soil to pupate. The pupal stage lasts for a further two to three weeks before adults emerge.
Host range
Most enquiries on rosemary beetle received by the RHS Members' Advisory Service concern the beetle as a pest on rosemary (Rosmarinus officinalis) or lavender (Lavandula species). However, the beetle is able to breed on thyme (Thymus species), sage (Salvia species), Russian sage (Perovskia species), and it is likely that other plants in the Lamiaceae plant family may also act as hosts.
Control
Rosemary beetle can be controlled either with insecticides or hand picking of adults and larvae. If pesticides are used then these are best applied in late summer to early autumn or in the spring, when the beetles and larvae are active on the plants. Suitable insecticides that can be used include bifenthrin, thiocloprid or imidacloprid. Insecticides should not be used while plants are in flower because of the danger to bees. Only the ready-to-use formulation of thiocloprid (Provado Ultimate Bug Killer Ready to Use) is approved for use on edible herbs.
Publications
Halstead, A J.
1996. Possible breeding by the rosemary beetle, Chrysolina
americana (L.), in Britain. British Journal of Entomology
and Natural History 9: 107-108
Salisbury, A. 2002. The Rosemary beetle, Chrysolina americana
(L.) (Col., Chrysomelidae) in Britain. Entomologists Monthly
Magazine 138: 77-80
Salisbury, A. 2003. Further records of Chrysolina americana
(Linnaeus) (Chrysomelidae) in Britain. The Coleopterist 12(2):
61-62