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Extension > Yard and Garden News > Say blister beetle

Thursday, June 25, 2015

Say blister beetle

Jeffrey Hahn, Extension Entomologist

There have been a number of reports of green beetles with orange legs in flower gardens. These beetles are ant-like, have soft wing covers and are about ¾ inch in length. This is the Say blister beetle Lytta sayi. They have been found feeding on a variety of flower blossoms, including roses, peonies, irises, and lupines. When they are abundant, they can cause serious damage to plants.

Say blister beetle close up.  Photo: Jeffrey Hahn, UMN Extension
All blister beetles secrete a defensive oil called cantharidin which can be very irritating and can raise blisters when skin is exposed to it. Fortunately, the Say blister beetle generally does not have a high enough concentration of cantharidin to cause severe problems to people.

If Say blister beetles are in your garden, there are several options for their management. Physical removal is a good management method. If there is concern about exposure to cantharidin and blisters, wear gloves to be on the safe side. If you are interested in a low impact insecticide, try spinosad or neem oil. You can also apply pyrethrins; to be effective this insecticide has to directly contact the insects. There is also no residual and it may need to be reapplied.
Say blister beetles on Addie Tischler peony. 
Photo: Jeffrey Hahn, UMN Extension
There are a variety of residual garden insecticides that can kill blister beetles, such as permethrin, bifenthrin, lambda cyhalothrin, and carbaryl. Take care when using these insecticides as they are toxic to pollinators (although spinosad is considered a low impact insecticide to beneficial insects, it is also toxic to bees). Do not treat plants when pollinators are active around them. Instead, treat plants during late evening or nighttime when pollinators are no longer active to minimize exposure to insecticides.

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