Rosemary beetle

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

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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 a leaf beetle (family Chrysomelidae) with about 250 species found in Britain. They all feed on plants, most are do not have a noticeable effect on garden plants, many are colourful and many species are  local or rare. 

Rosemary beetle eats the foliage and flowers of various aromatic plants, such as rosemary, lavender, sage, thyme and some other related plants.  In most circumstances teh beetle can be accepted as part of the life a healthy garden supports as it does not eat enough to harm healthy plants. It 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 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 this survey are stored permanently in an anonymised form in order to monitor the spread of the organism. 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

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. These leaves can be reduced to short stumps with greyish-brown discolouration where the damaged tissues have dried up. In most cases however, the overall appearance and health of the plant remains unaffected
  • The flowers can also be eaten

Control

Host plants often survive populations of this beetle without any noticeable adverse affects, control is not usually necessary and the beetle can be accepted as part of the biodiversity of a healthy garden.

Check susceptible plants frequently so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.

Non-pesticide control

  • Where possible tolerate populations of beetles, this beetle can usually be treated as a colourful addition to the garden
  • Remove beetles by hand where practical this 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
  • Encourage wildlife in the garden, such as birds, frogs and predatory ground beetles who will eat the larvae and sometimes adult beetles.

Pesticide control

The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.

Pesticides are likely to be more effective on larvae than adults and this beetle rarely causes significant damage to healthy host plants. 
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer). These pesticides although broad spectrum have a very short persistence and so may require reapplication to keep beetle numbers in check.
  • More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
  • A broad spectrum systemic insecticide containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available

Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number applications, spray interval and harvest interval.

Plants in flower should not be sprayed due to the danger to bees and other pollinating insects. Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

Download

Pesticides for gardeners (pdf document)

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. The eggs 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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