Green June Beetles

Dawne Howard
Frederick County Master Gardener

Sitting on my patio this second week in July, I gazed over my back yard and saw large flying insects hovering about 10-20" above the surface. I caught one of the insects and identified it as a Cotinis nitida ( Linnaeus) or, better known to most of us as the Green June Beetle.

The beetles are about an inch long and ½ inch in width. They are a dull velvety green in color on their top side and their underside is a bright metallic green with orange and yellow areas.

The female beetles lay their eggs in soil during the months of June and July. The eggs hatch in approximately 2 to 3 weeks and the young larvae begin to feed on decaying plant matter and humus. The larvae are creamy white, C-shaped grubs with dark brown heads. These grubs feed on the decaying vegetative matter during their first summer and then hibernate over winter in the soil. In their second summer, the grubs feed on the underground plant roots. They again hibernate over the second winter and in the third summer, during June and July, they pupate over a period of about 3 weeks.

These adults remain in pupate earthen cells in the soil until the following spring. Then they emerge to feed and start the cycle all over by laying eggs during that June/July period. This is now the 4th and final year of their life cycle. Largest broods appear at the end of the 4 year cycle.

These Green June Beetles feed on ripening fruit, plant foliage, grapes, potatoes, strawberries, corn roots, and some types of flowers. They are harmless to humans and animals, but they are somewhat of a nusense.

Biological controls like milky spore and insect-parasitic nematodes should be applied to the affected area in mid-June. Many of the beetle larvae will be parasitized by a type of digger wasp or blue winged wasp which are abundant during the month of August. These beneficial wasps lay their eggs directly on the grubs.

The timing of a chemical grub control product application is important. New systemic insecticides such as Merit granules can help broaden the window of application by several days. This systemic insecticide can give season long control as it can remain viable in the soil for up to 3 months.

Read other articles by Dawne Howard