Rain Beetles – Pleocoma spp.

Rain Beetles (Pleocoma spp.) Common Name: Rain Beetles Latin Name: Pleocoma spp. Appearance: Egg: The egg is white with a yellowish tint and has a smooth, dull surface. It’s oval and roughly 1/6 inch (4.5mm) in length. Larva: The larva is grub-like, with a curled, white body and a pale yellow-brown head. Mature larvae range from 1-3/4 to 2-1/4 inches (45 to 55 cm). They are creamy white, slack, and motionless at the prepupal stage. Pupa: Female pupas are white and range in size from 1-1/2 to 1-3/4 inches (35 to 45 mm), depending on the species. Male pupas are often smaller. Adult: The adult looks like a scarab beetle, having powerful legs for digging. It is hairy and dark or reddish brown. In the end, its antennae feature oval clubs of numerous lamellae or plate-like structures. Male antennae feature longer lamellae than female antennae. P. oregonensis females are 7/8 to 1 inch (22 to 25 mm) in length. P. crinita and P. minor females are around 5/8 inch (15 mm) long. Females are bigger than males and lack flight. In the adult stage, neither sexes feed. Host plant: Most deciduous fruit trees are vulnerable to Pleocoma larvae. Rain beetle larvae have caused root damage in apple, pear, and other orchard trees in California and apple, pear, and cherry trees in the Mid-Columbia area. Native hosts in the Mid-Columbia region include Douglas fir, Ponderosa pine, white fir, white oak, Oregon maple, vine maple, and black cottonwood. P. oregonensis also feeds on sagebrush. Territory: These beetles are mainly found in western North America. Damages caused by Rain Beetles: Larvae feed on fibrous roots, main roots, and underground trunk sections and reside in the soil in the root zone. Feeding damage can be superficial or deep, appearing on the root as patches or winding bands. Fruit trees that have been affected poor exhibit vigor, scant foliage, and minimal yields. Life history and habits: Rain beetles emerge in the field at different times, depending on the species. Adults may live for months without eating. Only male beetles can fly. After emergence, the wingless females return to their burrows or dig new holes into waiting for males. Males fly early in the morning and after fall showers. A sex pheromone released by females attracts them to females in their burrows. Females go deeper into the dirt after mating. They begin egg laying in April and continue until early July. Eggs are placed in a spiral pattern in burrows ranging in depth from 10 to 30 inches (25 to 75 cm). A female can lay up to 60 eggs, and from July through August, eggs hatch. Larvae molt once a year and live as larvae for 9 to 13 years before pupating. When the larvae reach maturity, they form pupal cells and enter an inert prepupal stage. Between late June and mid-August, pupae develop. The pupal stage lasts between 40 and 50 days.