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The blue mint beetle, Chrysolina coerulans, was detected breeding in the UK for the first time in July 2011, from Kent. Since 2012 the beetle has been found in Cambridgeshire, Lincolnshire, Hampshire, parts of London and Edinburgh. The beetle is of widespread occurrence on the mainland of Europe and it may spread further in Britain.
Blue mint beetle Image: RHS/Science
There is another beetle native to Britain, known as the green mint beetle, Chrysolina herbacea. This is 8-9mm in length and is a shiny emerald green. The black larvae are similar to those of the blue mint beetle. Pale green caterpillars of several moths, Pyrausta spp. loosely spin together foliage at the shoot tips with silk threads and eat the leaves. Some other species of moth caterpillar and slugs and snails also sometimes eat mint leaves.
There are several other metallic blue beetles found in the UK. They are unlikely to be found on mint. These include willow leaf beetles found on plants willows and poplars, the alder leaf beetle found on alder, and fuchsia flea beetle found on fuchsia, Zauschneria and wildflowers known as willowherbs, Epilobium spp. These other blue beetles are mostly less than 7mm in length. The leaf beetle that occurs on alder is about 7mm long. A rare blue form of the green mint beetle (see above) sometimes occurs.
Blue mint beetle can usually be tolerated, it is unlikely to be numerous enough to cause significant damage to healthy mint plants.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Alder leaf beetle
Broad been seed beetle
Chemical labels explained
Chemicals: using a sprayer
Chemicals: using safely and effectively
Citrus and Asian longhorn beetles
Flea beetles on brassicas
Fuchsia flea beetle
Ground beetles and rove beetles
Herbs and salad leaves: in growing-bags
Herbs in containers
Protect your garden
RHS statement on pesticides in horticulture
Willow leaf beetles
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