BEETLING THE COLD

Recent cold snaps have closed schools, stalled cars and stressed electricity supplies. But, come spring, there could be a small benefit from the extended deep freeze.

Because the long spell of sub-zero temperatures came when there was a lack of thick snow cover to insulate the ground, insects that burrow underground to survive the winter may have been harmed. That could mean fewer Japanese beetles and other garden pests come spring. There may also be a drop in the mosquito population.

All of this is speculative, warns James Dill, a pest management specialist with the University of Maine Cooperative Extension, because experts will not know the extent of the state’s insect population until spring comes and the bugs emerge. However, it is likely that the cold did kill off some overwintering bugs. “Biologically speaking, there should be an impact given these low temperatures,” Professor Dill said.

The insect most likely to die because of the extended cold is the Japanese beetle, a recent arrival in Maine. The beetle is currently at the northern edge of its range and the cold weather may prompt it to stop its northward invasion. A couple more very cold winters could seal its fate, according to Professor Dill.

The beetles overwinter in the grub stage when they burrow up into the soil, usually to a depth of 2 to 8 inches, although grubs have been found 6 feet under frozen ground with little or no snow cover. When the soil warms, they move upward cocooning in an earthen shell before emerging as the copper brown winged adults. Adults emerge from the ground and begin feeding on plants in June. Japanese beetles can feed on about 300 species of plants ranging from roses to raspberries to poison ivy.

Sudden cold spells with little snow cover often cause high mortality among the insects, according to the University of Illinois Extension service. Japanese beetle grubs are killed at soil temperatures near 15?F and die when soil temperatures are consistently around 32?F for two months.

Last year, portions of Illinois, such as the Chicago area, experienced winter conditions with little or no snow cover and cold temperatures occurred over an extended period. As a result, the university reported, the emergence of Japanese beetle adults was slow and late. Much lower numbers of the pest were reported in the areas of Illinois where the soil was frozen 15 to 30 inches deep. “It is possible that prolonged cold soils caused increased wintering grub mortality,” the university cautiously reported.

So, think of the beetle as you throw another log on the fire.