The blue willow beetle is a bronze-blue metallic insect that feeds mainly upon plants in the Salix genus. They fall within the leaf beetle family (Chrysomelidae) because both the larvae and adult beetles use the leaves of plants as the main food source. These beetles tend to aggregate on the host plant, so they can be significantly damaging some years. There are numerous species of leaf beetle that will use willow as a food plant, but the blue willow beetle is by far regarded the worst pest.
Beetles are known to contribute to pollination.
These beetles can severely defoliate trees in years where they are particularly abundant, but tree health is always regained in the following years.
Adult beetles are small and metallic. When the light reflects from the wingcases, you may see mixtures of bronze, green and dark blue. Colouring can be variable; rarer variations tend to be more bronze. They're only half a centimetre long, with tiny pores that form lines of indents on the wingcases. Larvae look very similar to ladybird larvae. They are small, black and highly segmented. They have creamy peach markings that run down the body.
Adult beetles and their larvae graze away the leaf surfaces which causes the leaf insides to dry out, ultimately turning brown. During years where they're abundant, these beetles can significantly defoliate trees.
Europe and America.
It can be very challenging to get rid of these beetles completely if the trees infected are tall. Host trees can tolerate willow beetle damage, where in most cases the plants achieve full recovery the following year.
Unfortunately, there is no effective means of treatment for these beetles. Damage tends to be sporadic with some years being notably worse than others.