Chrysolina americana is a pretty beetle commonly found on rosemary plants. Their attractive colouring makes them easy to spot, especially on a sunny summers day! This species is found in the leaf beetle family, Chrysomelidae. They feed primarily on the leaves of plants. Activity peaks from August-April, but the adult beetles can be found throughout the year. It's advised to check plants for adult beetles year-round and regularly. Brown tips in rosemary, thyme, sage and lavender should prompt a gardener to inspect plants!
Can strip foliage if in high abundance.
Predated by many garden predators.
Adult: Mature beetles are shiny metallic insects measuring roughly half a centimetre. They are colourful, boasting purple and green stripes running along the length of their thorax and wing cases. Larvae: The larvae are coloured grey-white with darker striping down their bodies. At full size they measure 0.8cm. Pupae: Currently unavailable. Eggs: Tiny, sausage-shaped dark red-brown eggs may be found in clusters at the end of herb branches.
Holes in leaves and flowers. Damage may be evident throughout spring and summer. Leaves turn brown following damage from feeding. Branches and leaves may be reduced to small stumps. Brown-grey grubs with black legs may be found on leaves and branches. Stripey, metallic beetles also may be found on the infested plant. Sausage-shaped eggs may be found at the end of branches beneath leaves.
Europe, Britain and Israel
Control is not always required; mild infestations do not dramatically harm the host plant species. Smaller plants are more at risk. 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 reflect light, making them easier to detect. For taller host plant species, place fabric or paper below the infected plant, then tap or shake the host plant to quickly collect the beetles underneath. Grub larvae can be collected by running kitchen towel gently over the branches of plants. Attract garden birds into your green spaces using feeders, tables, perching spots and baths.
Pesticides are recommended for heavy infestations that can't be controlled via 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 useful, such as deltamethrin or lambda-cyhalothrin. Please note* Thyme, lavender, sage and rosemary are all favoured by bee and hoverfly pollinators, so please take care if you are planning to spray your plants. We don't advise applications of pesticides when flowers are present. Always read instructions and make sure your plant is listed on the bottle if you intend to eat it.
These beetles are attracted to various aromatic herb plants in the mint family, Lamiaceae.