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I had an interesting discussion today in which the question arose how insects survive in the winter. Since they need a high enough external temperature to be active, this seems a bit difficult in the winter. With frost they should completely freeze and I don't think they will survive this. Do they rely on eggs laid in the fall (which have to survive freezing temperatures as well) or do they employ other techniques for that?
As there are many insects, there are also a number of different strategies. As you already said, insects depend on the temperature of the environment and cannot produce enough heat with their metabolism. The major strategies are:
- Communal living
- Cold tolerance (by means of antifreeze proteins)
Only some of the insects can opt for " Migration" , those which are big enough to travel long distances. A good examples for this migration of insects is the monarch butterfly which migrates from summer habitat in the north-eastern US and southern Canada to Mexico in the fall. Using this strategy the insects avoid live threatening temperatures.
"Communal living" helps insects to get over the winter, as the colony produces enough heat to survive. A prominent example are bees, which maintain relatively high temperatures in their hives, another would be ants.
"Antifreeze proteins" are also employed by a few. Some insects contain special proteins or glycerol in their hemolymph (the equivalent to blood) which either prevents it from freezing and/or prevents the formation of ice crystals which destroy the cells. An example for such an animal would be the New Zealand Mountain Stone Weta which can stay frozen for month until the temperature gets high enough for living again. Some insects go into some kind of winter sleep, in which they survive the cold temperatures. Their living cycle is synchronized with the seasons of the year.
The answer is based on this and this article, have a look for further information and references.
The above answer is perfectly correct… except it deals with mainly ectothermic insects… now there are some endothermic insects as well… & many of them adopt this following curious technique to elevate their body temperature…
Here the hawkmoth's capacity to elevate their body temperature depends on their powerful flight muscles which generate large amount of heat during when operating. The insects use shivering to warm off before they take flight… they contract their flight muscles in synchrony before flight, so that only slight wing movements occur but considerable heat is produced. Chemical reactions , & hence cellular respiration speed up their warmed-up flight motors enabling them to fly during cold days & even during night…
Also some endothermic moths take help of 'time-trusted' countercurrent heat exchanger, that helps to maintain a high temperature in thorax… where majority of flight muscles are located… thus maintaining a constant temp. of about 30 degree celcius at the body core when the outside temperature is,sometimes ,even near subzero…
Also… this particular mechanism is applied by insects & animals… ectotherms & endotherms alike… Introduction of cholesterol in the cell membrane thus hindering solidification at low temperture by disrupting the regular packing of phospholipids…
Insects survive the winter through a trick right out of science fiction
In the summer, when the air is sticky and hot, insects are everywhere: circling your fruit bowl, marching across your picnic, buzzing in your ear, and sometimes — the worst of times — flying directly into your mouth.
But when temperatures drop, icicles form, and parkas come out of storage, the bugs seem to vanish completely from the chilliest corners of the world — until months later, like some kind of magic trick. they reappear, as if they'd been there all along.
To find out, we talked to someone who has spent much of his research career pondering this very question: Brent Sinclair, the director of the Insect Low Temperature Biology Lab at the University of Western Ontario in Canada, where he is also an associate professor.
One reason most people are mystified by the fate of insects in the winter is because there is not a simple answer. Some survive as eggs, larvae, or pupae, while others make it through the winter as fully-grown adults.
In general though, there are three distinct survival strategies that get insects — and related critters, like spiders — through the winter. One of them (the last on our list!) seems strange enough to be science fiction.
How do insects survive the winter?
Right now, I have five different insects walking around my office! Of course, they are accidental invaders along with many other nuisance pests active right now. It’s also a sign of the quality of the building I work in [sigh]. I’ve been asked several times, “how cold does it have to get to kill insects?” Perhaps it is important to understand why cold temperatures kill insects. Insects are unlike mammals and birds because they must generate their own heat (called ectotherms). Insects die when they are exposed to temperatures below the melting point of their body fluids. If they want to survive our cold Iowa winters, they must avoid freezing or tolerate freezing. Over time, insects have developed several strategies to survive cold temperatures and none of them involve wearing fleece.
Boxelder bugs. Photo by Joseph Berger, www.ipmimages.org.
Some insects just move into human structures in the fall and keep warm until spring. A common example are the multicolored Asian lady beetles aggregating on and in houses every year. Even if they are protected inside, they will likely die before spring if they don’t get food and water. Some insects also migrate to warmer climates to avoid freezing. A classic example is monarch butterflies moving from Canada to Mexico every year. Sounds pretty good about now!
Multicolored Asian lady beetles mass on structures every fall. Photo by Robert Koch, University of Minnesota.
Most of our persistent insects in Iowa have to overwinter outside, and two strategies have evolved to survive extreme conditions: freeze avoidance and freeze tolerance. Freeze-avoidant insects keep body fluids liquid and freeze-tolerant insects can handle the formation of internal ice. Wait a minute, what? I know…either strategy seems fantastical.
The main strategy for insects living in the northern hemisphere, where we have cold temperature for long period of time, is freeze avoidance. Freeze avoidance can be achieved a few ways. Sometimes insects enter a “dry” hibernation by getting rid of all the food and water in their body. That way, ice can’t form inside the body and kill them. Water needs food or dust particles in order to crystallize water can cool down to -42°C without freezing if particles are absent. Other insects have a super waxy coating on the exoskeleton that protects against ice formation on the body. Amazingly, some freeze-avoidant insects also produce cryoprotectants, such as glycerol and sugar, to reduce the lethal freezing temperature of the body. So yes, cryoprotectants act like the antifreeze in your car. I can’t make this stuff up!
Most insects living in the southern hemisphere, where the climate is more variable, employ freeze tolerance. These insects can stand ice formation in the body. Some will actually initiate freezing their body at relatively high temperatures in order to prepare for a longer hibernation. An example of a freeze-tolerant insect is the woolly bear. [Side note: several winter festivals celebrate the woolly bears kinda like Groundhog's Day.]
Woolly bears overwinter as cold-hardy caterpillars. Photo by IronChris, Wiki.
No matter the overwintering strategy, all insects will eventually die if it gets cold enough. However, the lower lethal temperature is different for each species. Insects can overwinter in any life stage - some are belowground and some aboveground. It gets complicated quickly, and so I will save that for another time. Find out more about how insects survive the winter from this Wiki page.
Cold Hardiness of Insects and the Impact of Fluctuating Temperatures
Temperature often limits the distribution of an insect species, but it can also influence its success in the occupied range. This is because insects are ectotherms, meaning their internal body temperature changes with their environment because they do not generate heat. Therefore, insects are directly affected by microclimates caused by daily or seasonal temperature fluctuations in their habitats.
How do insects adapt to harsh environmental conditions?
Like hibernation in other animals, insects may go dormant in response to adverse conditions. Dormancy is an inactive state characterized by depressed metabolic activity and arrested development. This may take many forms depending on intensity and duration of dormancy. Quiescence is a short period of dormancy that is directly induced by adverse conditions and can be quickly reversible when favorable conditions return. Diapause is a hormonally regulated process that is genetically determined to occur during a certain life stage. Like quiescence, diapause is a response to environmental cues, but it is triggered in advance of the adverse conditions occurring to allow time for profound physiological changes to occur. Initiating and terminating diapause is a gradual response to token stimuli, such as photoperiod, temperature, food quality or availability, maternal factors (diet, age, etc.), moisture, and others. Reliable indicators of winter diapause in temperate climates include photoperiod and temperature. Diapause typically lasts for months but can occur for weeks or greater than a year, depending on the species.
Typically, insects build up energy reserves and move to a protected overwintering site (warmer climates, soil, litter/debris, structures such as cocoons and galls) in preparation for diapause. Entering diapause does not ensure survival. Insects quickly assume a temperature close to that of their environment, leaving the water in their body vulnerable to freezing. Diapause and cold hardiness are not always linked cold hardiness is sometimes achieved after diapause initiation. Physiological mechanisms involved with successful overwintering vary by insect species and are not fully understood. Here, we provide examples of some primary mechanisms that have been described for different strategies, but this is not an exhaustive list.
Freeze-tolerant insects can survive freezing by producing ice-nucleating and heat-shock proteins, increasing abundance of aquaporins, and accumulating cryoprotectants. Most freeze-tolerant insects freeze at relatively high temperatures to avoid the rapid formation of ice crystals that can cause injury. In freeze-tolerant species, no correlation exists between the supercooling point (SCP the point at which water freezes) and winter temperatures. However, repeated freezing can lower the SCP and increase cryoprotectant concentrations. Typical SCPs for freeze-tolerant insects are below -40°F (Figure 1).
Freeze avoidance is the most common adaptation to cold temperatures. Freeze-susceptible insects lower their SCP by producing antifreeze and heat-shock proteins and accumulating cryoprotectants to avoid freezing. They do not produce ice-nucleating agents but instead rid their bodies of ice nucleators such as food particles or microbes in the digestive tract. In freeze-susceptible species, lower SCPs are correlated with more severe winter temperatures. Mortality can still occur in freeze-susceptible insects if temperatures go below the SCP. Typical SCPs for freeze-susceptible insects are between -4°F and -40°F (Figure 1).
Rapid cold hardening:
Diapause requires a more prolonged response to cold temperatures, but insects can adapt on very short time scales as well. Rapid cold hardening (RCH) allows for almost instantaneous cold tolerance for brief exposures (minutes to hours) to non-lethal temperatures, particularly when the insect is not yet in a cold-hardy state. Survival from RCH improves tolerance to more severe temperatures later.
Because the SCP of most overwintering insects is well below the lowest winter temperature, the biggest threat to survival is the cumulative impact of non-freezing chill injury, which is a function of temperature and duration of exposure. This type of injury occurs above the freezing point but below normal developmental thresholds when insects are typically in a chill-coma. Most insects enter a reversible chill-coma at or below 50°F. Injury can be reduced or reversed if a cold period is interrupted by brief warm temperatures (as short as 5 minutes). This reduced mortality is not necessarily due to reduced chill injury, but rather a repair of chill injury during the warm spells.
When mortality does not occur, exposure to cold temperatures has sublethal effects such as reduced growth, development, and reproductive potential. Fluctuating temperatures can allow development outside of the normal critical limits however, development is typically delayed because direct cold injuries need to be repaired. If the lowest temperature does not cause injury, development may actually be accelerated. Fluctuating temperatures may reduce fecundity if stressful temperatures are experienced. Repeated cold exposures can increase survival and lower supercooling points relative to sustained warm or cold temperatures. Repeated freeze-thaw cycles have more mixed results survival is generally decreased but depends on species and increases with increasing recovery time.
Figure 1. Schematic of the biochemical differences between the freeze tolerance and freeze avoidance overwintering strategies of insects. From Bale and Hayward 2010. (doi: 10.1242/jeb.037911).
Overwinter – to survive the winter months in an arrested state of development, typically in a location that protects the insect from cold winter weather. Examples: migration, inside buildings, under rocks or tree bark, in leaf litter or soil.
Dormancy – the temporary suspension of development, growth, and physical activity during a part of an insect’s life cycle.
Quiescence – a short period of dormancy directly induced by adverse conditions that can be quickly reversible when favorable conditions return.
Diapause – a hormonally regulated state of metabolic activity that is genetically determined to occur during a certain stage. Growth and development are reduced, and insects have increased resistance to extreme conditions and reduced activity or altered behavior. Facultative diapause occurs in response to environmental cues, while obligatory diapause occurs during each generation regardless of environmental cues.
Freeze tolerance – the ability to tolerate frozen tissue by limiting the presence or location of ice in the body.
Freeze avoidance – the evasion of freezing by lowering the point at which water freezes in the body.
Supercooling – when water cools below the freezing point without changing to ice. If no particle is present to allow crystallization, water can cool to -36.5°F without freezing.
Supercooling point – the point at which a supercooled solution freezes.
Chilling – cooling without freezing, usually above 32°F.
Rapid cold hardening – a response to cold temperature that allows insects to survive short exposures by quickly decreasing their lethal temperature.
Cryoprotectants – examples include sugar alcohols such as glycerol, sorbitol, and inositol, trehalose, proline, and glucose.
Marshall and Sinclair. 2015. The impacts of repeated cold exposure on insects. J. Exp. Biol. 215: 1607—1613.
Sinclair, Addo-Bediako, and Chown. 2003. Climatic variability and the evolution of insect freeze tolerance. Biol. Rev. 78: 181—195.
Turnock and Fields. 2005. Winter climates and coldhardiness in terrestrial insects. Eur. J. Entomol. 102: 561—576.
Bale. 2002. Insects and low temperatures: from molecular biology to distributions and abundance. Phil. Trans. R. Soc. Lond. 357: 849—862.
Colinet et al. 2015. Insects in fluctuating thermal environments. Annu. Rev. Entomol. 60: 123—140.
How Insects Survive the Cold of Winter
Three months ago, our fields and forests buzzed and chirped with six-legged life: cicadas overhead, crickets underfoot. Now snow has blanketed the landscape, and they and most other insects are gone and won’t reappear until spring.
How do they survive this weather? What keeps them from freezing to death?
The risk of freezing is, in fact, a greater challenge for insects than for many other creatures in the natural world, and that’s because of their size. The smaller an animal, the more surface area it has relative to its mass and, consequently, the faster it loses heat from that surface/air interface. Even an especially robust bumblebee has much more proportional surface area than, say, an elephant.
The main problem posed by freezing is this: When water freezes into crystals, it expands. If this happens inside living cells, the crystals can squeeze against cell membranes and shred them, destroying tissues from the inside out.
In cold weather, most insects enter a state of diapause similar to – but physiologically distinct from – mammalian hibernation. In diapause they use little or no energy. However, insects, while in that state, still must avoid death from freezing.
Finding shelter is the answer for some. Ladybird beetles, cluster flies, and green lacewings sneak into our warm homes through cracks in walls. Females of the parasitic ichneumon wasps burrow into tree-stumps or clumps of moss to avoid harsh wintry blasts. A bumblebee queen will find refuge in a rotting stump, where she survives long after all the other members of her hive have succumbed to the cold.
Some insects generate high concentrations of antifreeze chemicals, collectively known as cryoprotectants, which prevent tissue from freezing or which limit the amount of damage caused by freezing. One cryoprotectant, glycerol, prevents ice crystals from forming inside the cells of certain insects. The grubs of longhorn beetles are an example. They survive by pumping themselves full of glycerol and then entombing themselves in deadwood.
Other species or the eggs of species, such as those of mantises, will freeze but only after producing other chemicals that will pull moisture from their cells, so that when ice crystals do form, they form in the spaces between cells. This mitigates damage.
Lepidoptera—butterflies and moths—are a diverse group that uses varieties of strategies to survive winter. The wooly bear, the tiger moth caterpillar, winterizes itself and crawls beneath leaf litter or between logs in your woodpile. The eastern tent caterpillar moth lays glyercol-laden eggs on cherry or apple twigs, where they remain throughout winter. The big, boldly-colored cecropia moth overwinters in a cozy cocoon of silk and wrapped-around leaves. Some lepidoptera, such as mourning cloak butterfiles, survive as adults, overwintering between shaggy tree bark or in hollowed-out trees.
One type of Lepidoptera, monarch butterflies, has it all figured out. They just go south. Monarchs in our region fly 3,000 miles to the volcanic mountains of eastern Michoacan in central Mexico each fall, where they join tens of millions of other monarchs from east of the Rockies. Monarchs live only several months, so the returnees to New Hampshire or Vermont belong to a second or third generation.
A few insects maintain a fairly active life throughout winter. A group of noctuid moths maintains body temperature by shivering. They can raise their body temperature by upwards of 50 degrees F. Be on the lookout for them flying around any time the temperature reaches 32 degrees or higher. For perspective, consider this: Temperature fluctuations of even about 5 degrees pose danger for humans.
One of the more elaborate survival strategies is employed by the goldenrod fly. Its life cycle is perfectly atuned to that of their namesake plant. In spring, adults lay eggs on the plant’s fresh green shoots. Chemicals, either delivered with the egg or produced by the larva, co-opt the plant’s growth, and cause the formation of a tumorlike sphere, called a gall, around the baby fly. The larva chews an escape tunnel in the fall but doesn’t use it instead, it retreats to the protective center of the gall, and awaits spring and its final metamorphosis. It’s easy to collect the growths from any stand of goldenrod in the fall dissecting them is a staple of field biology classes.
Most insects remain out of sight in winter, but on mild days, you may see ladybugs that have crept from the woodwork to soak up the sun, or on a walk with snowshoes in the woods, you may see snow drifts peppered with tiny snow fleas.
For snow fleas, the snow is not something to flee, rather it is a welcome banquet table at which to dine on such treats as pollen and algal cells. They eat while other insects sleep.
Kenrick Vezina is a freelance writer and teacher, who lives in Lowell, MA.
© by the author this article may not be copied or reproduced without the author's consent.
Winter stoneflies sure are supercool
Perhaps it&rsquos the summers I spent in college counting and identifying dragonflies and butterflies on the wing. Or maybe it was the hundreds of hours I endured in graduate school with my face dangerously close to a pan of full of muck, plucking out thousands of tiny stream insects. I reckon it&rsquos just a lifetime of curiosity for anything six-legged that permanently etched a search image for insects in my brain.
Thus, it&rsquos no wonder that, while enjoying a winter&rsquos day hike to one of my favorite waterfalls near Ithaca, New York, [Taughannock Falls, above] my eyes strayed from the scenic ice-glazed landscape to the tiny, dark specks moving nimbly across the snow: winter stoneflies were on the move! [Winter Stonefly in Hand, below]
Winter stoneflies are peculiar little creatures. In the dead of winter, the stoneflies&rsquo aquatic immature stages, called larvae or nymphs, crawl from their rocky bottom home up through cracks and crevices in the snow and ice that cover the surface of the stream they&rsquove inhabited for the last year and emerge as adults. Although in possession of four wings rolled neatly over their elongated abdomens, adult winter stoneflies stay close to the snow and ice, walking rather than flying, in search of mates.
All bundled up in my hat, mittens, scarf, parka, and long underwear (and still COLD), I wondered about the physiology of the winter stoneflies I observed. How can they be so active in sub-zero winter temperatures, when most of their six-legged brethren are well-hidden from the elements? And how do they avoid the lethal effects of freezing in two very different habitats, in water and on land?
Back in the cozy warmth of my home, I began to investigate some of these questions. I learned rather quickly that not much is known about the cold hardiness of aquatic insects, let alone the winter stoneflies (a name that refers specifically to two families in the order Plecoptera: Capniidae and Taeniopterygidae). In fact, in his treatise on stoneflies, the late Canadian field naturalist H.B. Noel Hynes proffered one possible reason why this is the case adult winter stoneflies, he muses, are "most abundant early in the season before the average entomologist has emerged from hibernation."
To understand how winter stoneflies deal with freezing temperatures in water and on land, it&rsquos useful to first examine what 60 years of research have revealed about how terrestrial insects, a more studied group, survive winter. If not clever enough to avoid winter altogether by migrating south (like those smart monarch butterflies) or seeking an insulated shelter such as your house (lady beetles and stink bugs, anyone?), terrestrial insects will prepare for the brutal cold of winter internally by undergoing a number of physiological and biochemical changes.
To understand these changes, cryobiologist Richard Lee, Jr. recommends we think of an insect as a tiny bag of water. In small, insect-sized volumes, water can actually be cooled many degrees below its standard freezing point (0°C) and still remain in liquid form, a process known as supercooling. You may have encountered supercooled liquids at some point this winter in the form of freezing rain. However, should a dust particle be introduced to a supercooled liquid, ice crystals will immediately begin to form around it in a process called nucleation. Additionally, ice can form inside the little bag of supercooled water if external ice crystals touch and subsequently invade it through any small opening, a process called inoculative nucleation.
Insects preparing for exposure to subzero winter temperatures, whether in an active or resting state, generally employ one of two strategies to achieve cold hardiness: avoid freezing or tolerate it.
Freeze-avoiding insects actively produce anti-freeze compounds &ndash including glycerol, proteins, and sugars &ndash that enhance their ability to supercool, allowing body fluids to remain unfrozen at temperatures even further below their freezing point. Some terrestrial insects&rsquo supercooled body fluids can remain in a liquid state at temperatures 15 &ndash 35°C below zero. Additionally, as winter approaches, freeze-avoiding insects will eliminate materials from their guts and body fluids that could serve as a seed around which ice crystals nucleate, including food, digestion-related bacteria, and dust.
Freeze tolerant insects, on the other hand, not only tolerate the formation of ice crystals in the fluids bathing their cells, but actively promote it. These insects produce ice-nucleating proteins in their extracellular fluid that actually limit the insects&rsquo ability to supercool and promote ice crystal formation at higher subzero temperatures. By promoting ice crystal growth outside the cells, the ice-nucleating proteins help reduce the likelihood that the contents within the insects&rsquo cells will freeze and burst. But with the water outside the cells bound up as ice crystals, water inside the cells will want to move into the extracellular space. To prevent subsequent cell dehydration and stabilize the cell membranes, freeze tolerant insects also produce the anti-freeze compound glycerol.
So how do these strategies translate, if at all, to aquatic insects, particularly the winter stoneflies?
Alas, before we tackle that question, let&rsquos consider the thermodynamic properties of the aquatic environments they call home for most of their life cycle. Water, as you may recall from high school physics, has a higher specific heat than air in other words, it takes more energy to heat water than it does to heat an equal mass of air. Consequently, the water in streams and rivers do not experience the extreme fluctuations in temperature that the air above them does and generally remains warmer than adjacent terrestrial habitats in winter. When ice forms on the surface of a water body, it actually insulates the water and substrate beneath it from sub-zero temperatures.
Dr. Lee and his cryobiology team bravely emerged from their winter hibernation to collect and compare the supercooling abilities of temperate zone aquatic and terrestrial insects in winter. Turns out, aquatic insects supercool much less than their terrestrial kin aquatic insects supercooled to about -7°C whereas terrestrial insects in the same families supercooled to temperatures as low as -40°C! Despite reduced supercooling abilities, most aquatic insects inhabiting these temperate waters are still classified freeze avoiders the relatively few aquatic insects known to actually tolerate freezing (specimens were actually collected directly from ice!) inhabit streams and ponds in the arctic that regularly freeze clear through the bottom. Dr. Lee and his colleagues hypothesize that overwintering aquatic insects living in the temperate zone simply do not encounter the extreme sub-zero temperatures that terrestrial insects do, rendering a super supercooling ability evolutionarily unnecessary.
Winter stonefly nymphs emerge as adults in the air pockets between the water and an insulating layer of surface ice, a fairly protected habitat that does not experience temperatures much below 0°C. Moreover, Dr. Lee and his colleagues have found that adult winter stoneflies collected in February had a significantly greater ability to supercool (i.e., they can cool to much lower temperatures without freezing) than their nymphal stages, suggesting adults can increase the amount of anti-freeze compounds in their body fluids.
Following emergence, adult winter stoneflies may seek protection in thermal refuges beneath the snow or under rocks that offer temperatures warmer than the subzero surface air. While the adults&rsquo brownish-black body coloration may promote the absorption of solar radiation, any such gains would likely be overridden by a cold breeze due to their small body mass. And by walking about on the tips of their feet, the adult stoneflies avoid the hazards of external ice crystals potentially invading their bodies and inducing inoculative freezing.
As our winter days grow longer and warmer in anticipation of spring, your opportunities to catch winter stoneflies in action this season will soon disappear. Here&rsquos a search image for you &ndash Commit it to memory. Now rouse yourself from that winter hibernation and go find those supercool little bags of water!
References and Further Reading
Borror D.J., White R.E. Peterson. (1970) A field guide to insects of America north of Mexico. Houghton Mifflin Co., New York. 404 pp.
Bouchard R.W., Schuetz B.E., Ferrington L.C., Kells S.A. (2009) Cold hardiness in the adults of two winter stonefly species: Allopcapnia granulata (Claassen, 1924) and A. pygmaea (Burmeister, 1839) (Plecoptera: Capniidae). Aquatic Insects 31 (2): 145-155 doi: 10.1080/01650420902776690
Frisbie M.P., Lee R.E. (1997) Inoculative freezing and the problem of winter survival for freshwater macroinvertebrates. Journal of the North American Benthological Society 16 (3): 635-650.
Hynes H.B.N. (1976) Biology of Plecoptera. Annual Review of Entomology 21: 135-153.
Lee R.E. (1989) Insect cold-hardiness: To freeze or not to freeze. Bioscience 39 (5): 308-313
Lencioni V. (2004) Survival strategies of freshwater insects in cold environments. Journal of Limnology 63 (Suppl. 1): 45-55.
Moore M.V., Lee R.E. (1991) Surviving the big chill: Overwintering strategies of aquatic and terrestrial insects. American Entomologist 37: 111-118
Walters Jr., K.R., Sformo T., Barnes B.M., Duman J.G. (2009) Freeze tolerance in an arctic Alaska stonefly. Journal of Experimental Biology 212(2): 305-312 doi:10.1242/jeb.020701
Photo credits: Taughannock Falls and Winter Stonefly in Hand, Holly Menninger, 2008 three Allocapnia sp. Winter Stonefly Closeups, Tom D. Schultz, 2001. All photos are used with permission and licensed under the Creative Commons.
About the author: Dr. Holly Menninger is a senior extension associate at Cornell University where she helps protect New York State&rsquos natural resources from the threats of invasive species, including a number of really big, bad bugs. With a Ph.D. in ecology and a fondness for insects with weird and wonderful life histories, she&rsquos determined to share her enthusiasm for the natural world by any means necessary, including podcasts, tweets (@DrHolly), and posing for pictures with 17-year cicadas on her nose.
The views expressed are those of the author and are not necessarily those of Scientific American.
The views expressed are those of the author(s) and are not necessarily those of Scientific American.
For Many Insects, Winter Survival Is In The Genes
Many insects living in northern climates don't die at the first signs of cold weather. Rather, new research suggests that they use a number of specialized proteins to survive the chilly months. These so-called &ldquoheat-shock proteins&rdquo ensure that the insects will be back to bug us come spring.
A study of flesh flies and a handful of other insects suggests that they have an arsenal of protective heat-shock proteins that are turned on almost as soon as the temperature dips. Until this new study, researchers knew of only two such proteins that were activated in flesh flies during cooler weather.
&ldquoInsects need heat-shock proteins in order to survive,&rdquo said David Denlinger, the study's lead author and a professor of entomology at Ohio State University. &ldquoWithout these proteins, insects can't bear the cold and will ultimately die.&rdquo
Denlinger and his colleagues found nearly a dozen additional heat-shock proteins that are activated during diapause, a hibernation-like state that insects enter when temperatures drop. Insects can stay in this state of arrested development for several months.
&ldquoWe certainly didn't expect to find that many proteins active during diapause,&rdquo Denlinger said. The researchers report their findings in the current online early edition of the Proceedings of the National Academy of Sciences.
Insects and other animals, including humans, produce heat-shock proteins in response to extremely high temperatures. The proteins are so named because they were initially discovered in fruit flies that were exposed to high heat. Humans make these proteins when we run a high fever.
"But insects make these very same stress proteins during times of low temperature as well as during exposure to high levels of toxic chemicals, dehydration and even desiccation," Denlinger said.
He and his colleagues first figured out how many genes were turned on only during the flesh fly's dormant state. The researchers extracted and compared RNA from both dormant and non-dormant fly pupae &ndash the developmental stage between larva and adulthood. They used a laboratory technique that let them separate out genes that were turned on only in the flies in this dormant state.
The researchers found 11 previously undiscovered genes that turn on heat-shock proteins during diapause. Until this study, they had only known of two such proteins.
Denlinger and his team also examined the expression of one of those previously discovered heat-shock proteins, Hsp70, in five additional insect species that aren't related to the flesh fly. Each insect is a fairly common agricultural pest: the gypsy moth, the European corn borer, the walnut husk maggot, the apple maggot and the tobacco hornworm. Collectively, these species cause millions of dollars of damage annually.
Hsp70 was active while all of the insects were in diapause.
When Denlinger's team knocked out the Hsp70 gene that makes the heat-shock protein, the insects were unable to survive at a low temperature (in this case, insects were exposed to -15°C, or 5°F.)
&ldquoThis underscores the essential role of this gene for winter survival, suggesting that this particular heat-shock protein is a major contributor to cold tolerance in insects,&rdquo Denlinger said. &ldquoIt's highly likely that the other heat-shock proteins we found during diapause in the flesh fly are also important to an insect's ability to endure months of cold temperatures.&rdquo
Denlinger has no plans to develop a method to get rid of heat-shock proteins in insect pests, but he says that it is important to understand how insects survive through the winter.
&ldquoThere may be steps we can take to disrupt the diapause process and make an insect vulnerable to low temperatures,&rdquo Denlinger said. &ldquoAt this point, the findings broaden our palette of players that contribute to cold tolerance in insects.&rdquo
He said the next step is to figure out the unique functions of each heat-shock protein.
&ldquoWe assume it's not simply redundancy in the system, but that each protein makes a unique contribution somehow,&rdquo Denlinger said. &ldquoThis protective mechanism is much more complex than we envisioned.&rdquo
Denlinger conducted the study with colleagues from Ohio State the U.S. Department of Agriculture's Agricultural Research Station in Fargo, N.D. the Harvard School of Public Health and Liverpool University in the United Kingdom.
Funding for the work came from a USDA-National Research Initiative Grant, the National Science Foundation and the National Institutes of Health.
Materials provided by Ohio State University. Note: Content may be edited for style and length.
Revealing the Secrets of the 'Winter World'
Revealing the Secrets of the 'Winter World'
Biologist Bernd Heinrich does much of his research from his hand-built log cabin in the snowy woods of Weld, Maine. Josh Rogosin, NPR hide caption
The imprint left by the wings of a raven landing on the snow. Heinrich attracts ravens to the woods near his cabin by leaving out carcasses for the birds. Josh Rogosin, NPR hide caption
An illustration of Golden-crowned kinglets from Winter World . Not much bigger than walnuts, these tiny birds forage from dawn to dusk and survive the winter eating insects. HarperCollins hide caption
After years of trying to figure out where kinglets went at night, Heinrich spotted these four birds, which look like one ball of fluff, huddled together on a branch. Bernd Heinrich hide caption
In his new book, Heinrich reveals the ingenious tactics animals in his local woods use to survive the harsh realities of winter. HarperCollins hide caption
University of Vermont biology professor Bernd Heinrich has always been fascinated by nature. From the age of 10 he grew up in Maine, spending his time exploring the wilderness and collecting insects, birds and other creatures.
The researcher, author and nature illustrator has written numerous books on the natural world. When he's not at work in Vermont, he spends his time in the forests of Weld, Maine. There, he has built by hand a log cabin that serves as the base camp for his research into the wildlife that populates the nearby woods.
At the moment, he's fascinated with how northern creatures survive the winter. In January, Heinrich published a book on his observations entitled Winter World: The Ingenuity of Animal Survival . Recently, NPR's Andrea de Leon spent the day with Heinrich exploring the secret lives led by animals in winter.
Trekking through the woods in temperatures well below freezing, Heinrich points out many subtle signs of wildlife activity that would go unnoticed by the untrained eye. In a thicket of tree branches, he stops at what appears to be a mass of cobwebs. Inside are tent caterpillar larvae, waiting out the winter. He explains that these creatures make their own glycerol -- otherwise known as anti-freeze -- to survive the cold climes.
Tiny stacks of pine cones and apples, he reveals, are probably the secret stash of an unseen tree squirrel. A disorderly pile of twigs turns out to be a raven's nest. Wing imprints barely visible in the snow suggest the bird's landing site. That's Heinrich's doing: he likes to leave carcasses out near his cabin to draw the ravens close.
"I like to have them around," Heinrich says. "I know the pair over there [in the nest] and so I want to make sure they have something to eat. I think right now it might be kind of hard for them."
The snow, Heinrich explains, isn't deep enough to trap the deer anywhere. That means deer aren't dying of starvation -- and therefore, no carcasses to provide food for the ravens.
It's this kind of attention to the tiniest details that makes Heinrich such a keen observer of the natural world. Among his recent discoveries: Red squirrels bite hundreds of tiny holes in maple trees, holes they remember and return to when the sap begins to flow.
One of Heinrich's favorite animals to ponder is the Golden-crowned kinglet. Kinglets, he explains, are in flagrant violation of what's known as Bergman's Rule, which states that northern animals are larger because they need big bodies to conserve heat. But kinglets are miniscule, weighing about as much as two pennies. They forage from dawn to dusk without stopping and survive the winter eating insects. And at dark, they seem to vanish.
"They're so small and their coloration blends with the foliage, so you don't really see them except through movement," Heinrich explains. "A lot of time they will hover in front of branches like a hummingbird."
A few weeks ago, after years of trying to figure out where kinglets disappeared to, Heinrich spotted four of the birds huddled together on a branch for the night. In his photograph, they look like a single ball of fluff, tiny tails protruding in different directions.
It's the kind of discovery that keeps Bernd Heinrich going back to the woods, his head full of ever more questions.
"I'm still trying to see something new all the time," Heinrich says. "So I would say that what a good day is, is seeing something that I hadn't seen before."
How Insects Spend the Winter
I consider the lack of biting insects and other invertebrates, to be a wondrous gift of the winter season. I can wander unmolested through wood and field absent the attentions of mosquitoes, deer flies, and ticks. And aside from a short list of &ldquousual suspects,&rdquo insects are a rarity to be encountered in the winter woods.
This begs the question: where do the insects go in winter? The short answer is &ldquopretty much everywhere&rdquo &ndash and in every insect life stage: as eggs, larvae/nymphs, pupae, and adults. Where and how each species makes it through the winter season depends very much on the individual species. While some insects, like the monarch butterfly, fly south for the winter, others have adapted to be able to stay here through the colder months.
Many aquatic insects go about their submerged lifestyles as they did in other seasons, just with the addition of an icy glass ceiling. Colder water holds more oxygen, which is an advantage for these insects, and at least some predatory fish slow their foraging activities in frigid water. Most aquatic insect larvae and nymphs do the bulk of their feeding and growing in winter and emerge as non-feeding adults in the other seasons.
Terrestrial insects employ diverse strategies to weather winter conditions. Mourning cloak butterflies and several other species hibernate at temperatures well below freezing. After reducing the water content of their bodies by as much as a third, they produce antifreeze compounds, such as glycerol or sorbitol, to prevent the formation of tissue-destroying ice crystals. They hunker down under tree bark or in tree cavities and wait out the deep freeze. In spring, they open their wings, and bask in the sun to get warm enough for flight. Their dark wings and bodies help with the solar heating, and dense hair helps trap the heat.
Honey bees, European immigrants like myself, team up to form a winter cluster around their queen. A bit like a three-dimensional rugby scrum, winter clusters straddle several honeycombs and in large hives can exceed basketball proportions. As temperatures fall, honey bee metabolic rates increase, keeping the bees substantially warmer than the ambient temperature. The bees on the outside of the cluster serve as an insulating layer trapping the sugar-fueled heat.
You may have also encountered some insects trying to make your home theirs to survive the winter chill. Box elder bugs and Asian ladybeetles move into structures, where we see them coming and going in fall and spring.
Many insects spend the winter as eggs that simply hatch into a new generation when the weather improves. There are examples too numerous to mention, but my personal favorite, at least in terms of their parental care, is the gypsy moth. Before the big chill arrives, female gypsy moths lay eggs in dense clusters around the bases of trees. The female pulls hair from her own body and uses silk to attach it to the egg cluster, providing some modicum of protection from the elements. The hairs are irritating to the touch and may also serve against predators. Spring hatchlings use silk of their own making to &ldquoballoon&rdquo away on the wind, Charlotte&rsquos Web style.
The list of winter pupating insects is also long among the more familiar are some members of the swallowtail butterfly family (Papilionidae). The familiar tiger swallowtail and the eastern black swallowtail both spend the winter secure in silken pupal cases spun by the larvae. All appears quiet in a chrysalis to the casual observer, but the stillness belies the cellular migration that transforms the caterpillar body into a butterfly. This process is driven by daylength and temperature, cues than ensure successful timing of butterfly emergence in spring.
And what about those winter wandering &ldquousual suspects&rdquo I mentioned above? I&rsquove taken a few rambles this winter to see who might be braving the snow. My December trips were a bust as far as insects went, but January has yielded dozens of non-biting midges, small winter stoneflies, a cranefly in the genus Trichocera, and an energetic snow scorpionfly backpacking his mate about the place. The cranefly even mustered a brief flight when it grew tired of me placing it on my glove for a better photograph. What brought such an abundance of mid-winter insect life? I have no idea, but I&rsquom taking it as a good omen for 2021!
Declan McCabe teaches biology at Saint Michael’s College. His work with student researchers on insect communities is funded by Vermont EPSCoR’s Grant NSF EPS Award #1556770 from the National Science Foundation.
© by the author this article may not be copied or reproduced without the author's consent.
Mosquitoes in the Winter?
Our battle against biting insects may rest a bit during the winter months, but it is never over. Temperatures drop and ice forms &ndash but mosquitos, midges and black fly eggs are waiting beneath a protective layer of ice or carefully hidden in some other shelter. When the spring thaw arrives, these insects return.
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