June Beetle

June Beetle, Vancouver Island, BC
June Beetle, Vancouver Island, BC, Photo By Bud Logan

The June Beetles are found west of the Rocky Mountains. Larvae feed on the roots of plants and the adults feed on foliage. Infestations spread as mated females tend to stay in one spot and the long time span of each generation, which can be four to five years before they reach sexual maturity in the pacific northwest.

Hosts of the ten-lined June beetle larvae probably include all deciduous fruit trees that grow in the Pacific Northwest. Infestations in most fruit tree orchards have been associated with apple trees. Other hosts include strawberries, cane fruits, roses, potatoes, corn, willow, and poplar.

Eggs are large, oval, and dull, creamy white. They can measure up to 4 mm long. The grub is a typical C-shaped scarab larva. The first instar is less than 12 mm long, while the full-grown third instar is 30 to 50 mm long. It has a brown head and three pairs of legs on the thorax. The pupa is preceded by a prepupal stage. The pupa is cream to light tan, about 25 to 40 mm long, with external wing pads. The adult beetle is 30 to 45 mm long. It is brown with conspicuous white stripes on the elytra, pronotum, and head. Its antennae are clubbed.

June Beetle, Vancouver Island, BC
June Beetle, Vancouver Island, BC, Photo By Bud Logan

On the male, the lamellae of the club are long, flat, tongue-shaped plates and the club is one and a half times as long as the rest of the antennae, these are used to sense females. The female has a shorter, more compact club, about 1/2 to 1/3 as long as the rest of the antenna.

The larval period can last 2 to 4 years in the Northwest, depending on the length of the growing season. Older grubs are found in the top 25 cm of the soil, where they feed on woody roots, while younger grubs live deeper in the soil and eat the finer and more tender roots. Most of the damage to the tree is done by the older grubs. The grubs begin to pupate in May and June. The pupal period lasts about 5 weeks. The adult bores an emergence hole from the pupal cell to the soil surface but may not emerge immediately.

Adults stay undercover during the day, hiding in plants and grasses. They make a strange hissing noise when disturbed. They become active in the evening and stay active longer on warm nights, but there is little activity when temperatures dip below 20 c. Males are attracted to females by a sex pheromone. They mate near the female’s emergence hole, and she will often lay her eggs in the same hole.

Females lay 60 to 70 eggs in the soil. The eggs hatch in about 3 to 4 weeks. Young larvae feed on decaying vegetable matter or fine roots. They take 3 to 4 years to develop fully. In cold winter climates, larvae may move deeper in the soil in winter and almost hibernate and move closer to the surface again in the spring to continue feeding.

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