European chafer biology & life cycle
There is one generation per year. The pest over-winters as larvae in the soil below the frost line. The larvae will migrate closer to the soil surface in April to mid-May where they will feed on plant roots. Larvae pupate in mid-May to mid-June. Adult beetles emerge from the soil in early June and early July to mate. During this time, the beetles can be seen swarming at dusk and will fly towards tall objects (trees or other landscape) to feed and mate. The adult females will then locate a cool, moist, nearby field to lay their eggs. The eggs will hatch and the larvae will feed on roots in late July until the ground freezes. The larvae will then move down to over-winter. The damage is done by the larvae (grubs). They feed on the fibrous roots of plants and cause them to become stunted and wilted. However, if the plants are larger and actively growing, as in the case of Soybeans, the damage may not be apparent. European Chafer tend to feed earlier in the spring and longer in the fall than other grub species. The adult beetles feed at dusk on deciduous trees but, even when the numbers are high, they seldom cause significant damage.
