Rosemary beetle

The rosemary beetle (Chrysolina americana) originates from southern Europe and has been found in Britain since the mid-1990s. The larvae and adults feed on the foliage of rosemary and related plants.

Rosemary beetle

Rosemary beetle

Quick facts

Common name Rosemary beetle
Scientific name Chrysolina americana
Plants affected Rosemary, lavender, sage, thyme and some other related plants
Main symptoms Foliage eaten where beetles and grubs have been feeding
Most active August-April; adult beetles present throughout the year

What is rosemary beetle?

Rosemary beetle is an insect that eats the foliage and flowers of various aromatic plants, such as rosemary, lavender, sage, thyme and some other related plants.

Rosemary beetle has spread rapidly since first being found breeding in central London in the late 1990s. It is now widespread throughout England and Wales. It is established in Scotland, present in Northern Ireland and may be established in parts of the Republic of Ireland.

Both the adult beetles and the larvae feed on the foliage and flowers of host plants, and are most active between late summer and the spring. 

Survey

Seen the rosemary beetle? We would like to know.

As part of RHS research we would like to know where the rosemary beetle has been seen.

Please submit your records via our rosemary beetle survey (expected time to complete survey = two minutes).

Submissions to our pest and disease surveys are stored permanently in an anonymised form in order to monitor the spread of the pest or disease. We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.

Thank you to everyone who has submitted records – read a blog about the surveys

Watch an animated map of the results from the Rosemary beetle survey (links to YouTube)

Symptoms

Rosemary beetle is fairly easy to spot;

  • The adult beetles are shiny insects, 6-7mm long, with metallic purple and green stripes on their wing cases and thorax
  • The larvae are greyish-white with darker stripes running along their bodies; when fully grown the larvae are 8mm long
  • Both the adult beetles and the larvae feed on the leaves, which can be reduced to short stumps with greyish-brown discoloration where the damaged tissues have dried up
  • The flowers can also be eaten

Control

Host plants often survive light infestations without any noticeable adverse affects and so control is usually always necessary.

Non-pesticide control

Hand picking can help to keep beetle numbers below the level at which serious damage occurs. With the taller forms of rosemary and lavender, the beetles and larvae can be collected by tapping or shaking the branches over newspaper spread underneath the plant.

Pesticide control

  • Pesticides are likely to be more effective on larvae than adults
  • If the plants are being used for culinary purposes, herbs must be listed on the product label and the label instructions must be followed, particularly the harvest interval that needs to be left between treatment and using the leaves
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several application of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

During mid-summer rosemary beetle can be present on host plants as adult beetles that usually do little or no feeding. In late summer they commence feeding, mating and laying eggs. These hatch after about ten days and both adults and larvae will feed on the foliage throughout autumn to spring during periods of mild weather.

When fully fed, the larvae go into the soil to pupate. Adult rosemary beetles emerge from pupae in the soil in early summer. There is one generation a year but because the adults are long-lived, there can be some overlap between the new and old generations of adult beetles. Because of this, adult beetles can be found at almost any time of year.


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