June and Japanese beetles and European chafers belong to the order Coleoptera and the family Scarabaeidae. The adults are easy to identify, but their larvae are very similar. They undergo complete metamorphosis (holometabolic insects): before reaching adulthood, they pass through the egg, larva and pupa stages.
Eggs: May be spherical, oval or elliptical, and are white. European chafer eggs turn grey a few days after being laid.
Larvae: Whitish, C-shaped bodies, with a brown head and three pairs of spiny legs. They grow to 2 to 3 cm, depending on the species.
Pupae: They look like little mummies, with their legs, wings and antennae closely folded against their bodies. They do not feed and remain immobile. They are yellowish or brownish.
June beetles (Phyllophaga anxia), also called May bugs, May beetles or June bugs, are large dark brown, almost black insects, about 2.5 cm long. They have short antennae ending in a large club of flattened plates. There is a small tooth at the tip of the pincers at the end of their legs.
The life cycle of June beetles extends over three years. They overwinter in the soil as larvae or young adults.
In spring, between mid-May and mid-June, the adults emerge from the ground. They take flight at dusk and swarm in trees to mate and feed on leaves (ash, birch, elm, maple, oak, poplar, willow, etc.).
After mating, the females lay about 50 eggs in small earthen balls, burying them in the soil in grassy fields or lawns. The eggs hatch about a month later. During their first summer, the young larvae feed mainly on plant litter. They moult into the second instar before migrating deep into the soil for their first winter.
In the spring of their second year, the larvae (2nd instar larvae) make their way back to the surface, where they feed until late June. They then become 3rd instar larvae, the stage when they do the most damage. In fall, they again burrow deeply into the ground.
In their third year, the larvae feed until June. They then close themselves up in cases where they pupate before emerging as adults, which remain in the soil until the following spring.
European chafers (Amphimallon majalis) are similar to June beetles, only smaller, about 1.5 cm long and coppery brown. Their complete life cycle lasts one year. The insects overwinter in the soil as larvae.
In early summer (late June, mid-July), the new adults emerge from the soil. At dusk, the insects swarm into trees to mate, but do very little feeding, merely nibbling the edges of leaves. The females lay an average of 20 to 30 eggs, burying them in the soil.
A few weeks later (late July, early August), the young larvae (1st instar larvae) appear, and feed until the second or third week of August. After two moults, the larvae (3rd instar larvae) burrow deeply into the ground for the winter. They pupate (late-May) and then emerge as adults early the following summer.
Japanese beetles (Popillia japonica) are metallic green and about 1 cm long. They have bronze wing covers and tufts of white hair on either side of their abdomens. Their life cycle usually lasts one year. These insects overwinter in the soil as larvae.
The adults emerge from the ground in July to feed and mate. Unlike June beetles and European chafers, they are active in the daytime. The females lay their eggs in the soil (40 to 60 eggs) and the larvae hatch two weeks later. They feed on roots until fall. After two moults, the larvae (3rd instar larvae) burrow into the ground for the winter.
The following spring, the larvae make their way to the surface to feed. They pupate (mid-June) and then emerge as adults in early July.