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Rosemary beetle

Chrysolina americana

Chrysolina americana is an insect commonly known by the name rosemary beetle. This species resides in the leaf beetle family, Chrysomelidae. They are at their most active from August-April and adult beetles may be found throughout the year.

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Detection

Appearance
Shiny beetle insects measure around 0.6-0.7cm long, they are colourful with metallic purple and green stripes running along the length of their thorax and wing cases. Larvae are coloured grey-white with darker striping down their bodies. At full size they measure 0.8cm long.
Symptoms
Damaged leaves and flowers from feeding activity. Most damage occurs between late summer to spring. Damaged leaf tissue acquires a grey-brown discolouration as they dry out and leaves can be reduced entirely to small stumps.

Personality

Order
Coleoptera
Family
Chrysomelidae
Distribution
Native to southern Europe and now commonly found across North Africa, the Near East and the Middle East. Present in Britain since 1994, widespread in London by 2002 and now found across the entire UK.

Biological treatment

Control is not always required, mild infestations do not dramatically harm the host plant species. Hand-picking of the insects as they appear can maintain rosemary beetle populations at a manageable level. Searching with a flashlight in the dark is ideal as their metallic bodies are easier to spot. For taller host plant species, it is recommended to place fabric or paper below the infected plant, then tap or shake the host plant to easily collect the beetles underneath.

Chemical treatment

Pesticides are more effective on adult beetles than their larvae. These are recommended for heavier infestations that are not manageable by hand-picking. Take care with chemical control if the host plants are to be used for cooking. Some chemical treatments for rosemary beetle include organic insecticides with natural pyrethrins. Several applications may be required for full control. Synthetic pyrethroid pesticides are also effective, such as deltamethrin or lambda-cyhalothrin. Do not spray when plants are flowering as this can be extremely harmful to pollinating insects!

Attracts this pest

Various aromatic herb plants in the mint family, Lamiaceae. Chrysolina americana feed mainly on rosemary, lavender and thyme species.

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