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Beetles are Supercool! Understanding the Life Cycle of Mountain Pine Beetles
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Mountain pine beetles are important to the Western United States. They have a very special life cycle, that includes staying “supercool,” or dormant, for most of their life. The scientists in this study want to know how this important life cycle could be affected by our changing climate.
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Many plants and animals live in annual cycles. They respond to seasonal temperature changes and changes in the length of the day. Some scientists are interested in studying the effect of these seasonal changes on the life cycle of plants and animals. The science that investigates these effects is called phenology . The science of phenology also investigates the influence of climate on the life cycle of plants and animals. This is important, because many scientists now believe that our climate is changing. In this study, the scientists were interested in understanding how a change in climate might affect the life cycle of a particular species of beetle. Because they could not wait a hundred or more years for the climate to change, the scientists used a computer program to predict what might happen.
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Mountain pine beetles (Dendroctonus ponderosae Hopkins) are sometimes supercool! This is what scientists call the beetles'ability to 'chill out' during the cold winter months, during their larva stage (Figure 1). During the winter, the beetle larvae live in the interior of pine trees. Because mountain pine beetles are composed partly of water, they must have made adaptations to keep from freezing in the cold of winter. When water freezes, it forms six-sided crystals. The crystals have sharp edges that could damage the other structures inside of the beetle. Mountain pine larvae have found a way to metabolize carbohydrates, which contain water, into glycerol during the winter months. Glycerol is a form of alcohol, and therefore will not freeze '" it is insect antifreeze! When the temperatures turn warm again, the larvae turn the glycerol back into carbohydrates. Carbohydrates are a source of energy for the beetles. Mountain pine beetles have adapted to cold conditions, and this allows them to survive.
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