Native to the western U.S. and Canada, adult ten-lined June beetles (Polyphylla decemlineata) are large (approx. 3 cm), dark-coloured scarab beetles, boldly marked with 10 whitish stripes. Adults produce a hissing sound when held gently between two fingers.
The large white grubs or chafers grow to a size of 3-4 cm over a 3-4 year developmental period while feeding on the roots of grasses and various other plants.
June beetles can occasionally damage the roots of grapes newly planted in land previously in pasture. The following description of damage to tree fruits by June beetle larvae, from the BC Tree Fruit Production Guide, is applicable to grapes:
When grass or orchard land preparation for planting trees destroys food plants, white grubs will feed on the fine root hairs and smaller roots of the transplanted trees. The trees gradually weaken and eventually die from lack of water and attack by wood-boring insects.
Feeding of adults on foliage causes little damage.
Other species of June beetles (June bugs) occur in the southern interior of B.C., but the C-shaped white larvae (white grubs) of these smaller, brown coloured beetles do not cause any significant damage to grapevines.
There are no insecticides registered for the control of June beetles. Control is achieved through fallowing and preparation of land prior to planting a new vineyard.
