Most of the country has had a mild winter this year. This often means more insects and pests during the growing season. Maybe as a harbinger, a brown marmorated stink bug has been seen already at Fordhook Farm, home of W. Atlee Burpee.
I think that we in temperate climates (most of North America) are blessed. In the tropics, consistent warmth and moisture and an endless summer relentlessly spawn generation after generation of insects and pests.
Consider the great 19th century English linguist and explorer Sir Richard Burton. Burton, who was nominally a Christian, is well known for making a pilgrimage to Mecca, Islam’s most holy site, disguised as a Pashtun chieftain. He was the first European to explore Central Africa where he located Lake Tanganyika and Lake Victoria. In Africa, Burton was so sick from insect-borne tropical diseases, that he was unable to walk for much of the trip. And trips were much longer in those days. His colleague, John Hanning Speke, whom he hated as much as Speke hated him, was temporarily blinded by disease and was deaf in one ear from an infection caused by a botched attempt to remove a beetle from his ear. It was Speke, whom Burton—too sick to move—sent off to be rid of, who discovered the long-sought source of the Nile.
For us, it seems that every year brings a cleansing winter that kills off insects and other pests. There’s truth to that, but it’s an overly simplistic view. Winter kills many insects and limits the number of generations possible in a year, but our temperate-climate insects have plenty of ways to cope with cold weather.
In fall, for instance, Monarch butterflies from all over North America leave cold weather behind and go south. They gather in huge groups and overwinter in trees in Mexico and southern California. In the spring, when the temperatures warm again, they fly home.
Insects do not control their temperature the way we do. They are at the mercy of their environment. But at the same time, they have no need to eat constantly to maintain a stable body temperature. When it gets cold, many of them burrow into the soil and enter a state of temperature-induced low metabolic activity that they can maintain as long as necessary. Soil temperatures remain relatively stable throughout winter; snow acts as an additional insulating cover. Unusually bitter or early cold or years without snowfall may kill these insects but not usually and not all of them.
Insects in very cold areas freeze solid—more or less. The insect’s cells do not actually freeze, but water in its interior does. This internal ice draws water out of the cells, increasing the cellular concentration of sugars and proteins (mostly) within insect cells, which further lowers their freezing point. Delicate cell membranes are not injured, and when the weather warms, the ice melts and the insect comes back to life.
Insects that live in mildly cold areas that cannot tolerate freezing protect themselves with antifreeze. They synthesize compounds (polyhydroxy alcohols) that allow them to “supercool” and survive (without freezing) temperatures well below 32° F. Among these compounds is ethylene glycol, the same that we use in cars. They’re out of luck, though, if temperatures drop below the point where their antifreeze works.
But what about this year? Will we have a scourge of insects this year? It’s too early to tell really. It’s true that more insects than normal will survive the mild winter. But spring is twelve days away, and the possibility for winter weather remains. Insects that normally would have remained quiescent longer may have been coaxed out by the unusually mild conditions. Temperature fluctuations could kill them. Then there are the parasites, predators, and diseases of insect adults, larvae, and eggs that may also be active earlier than normal and may cut insect numbers.
Nevertheless, without further winter weather and all else being equal, insects and other pests will get an early start this spring. In Pennsylvania, the brown marmorated stink bug (late of Asia) has a single generation in a year. Under a longer, warm spring and summer, it could manage two or three generations; four to six generations per year have been recorded in parts of China where it’s native.
Aphids overwinter as eggs and hatch in spring when temperatures warm. Most aphid species go through numerous generations during the growing season. This year more eggs may have survived and, combined with earlier hatching, there could be earlier, more severe infestations. These will cause wilt and yellowing or distorted and stunted plant growth. And aphids transmit viruses to many plants.
Buckle up because there may be more mosquitoes, fleas and ticks this year too. Mosquitoes overwinter as adults and are always out in early spring. They lay their eggs in standing water and complete the cycle from egg to biting, adult mosquitoes in a few weeks. In a warm, moist spring, mosquito populations explode. While our mosquitoes don’t carry the typically nasty diseases for which they’re known in the tropics, they still spread La Crosse encephalitis, West Nile Virus, and (for your dog) heartworm. Additionally, there’s their high annoyance factor.
Fleas could get in extra generations this year and could be a full-blown problem by summer. They like warm, humid conditions, and in the humid days of summer, your house will tend to be humid too. They’ll love your carpets—and possibly your socks, from which they’ll attack your ankles. Watch your pets and vacuum their sleeping areas regularly to remove flea eggs and suppress subsequent generations.
Then there are ticks (arachnids, not insects). Mild winters may or may not affect their populations. But nice weather draws people to tick territory where most cases of Lyme disease are contracted from the tiny nymphs that are most active in spring and early summer. Watch where you go outdoors and check your body over at the end of each day.
In the meantime, enjoy these last days of winter.