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Growing Degrees for Insects
Tue Dec 28, 2004
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Growing Degree Days for Insects, coming up on The Weather Notebook.
Hi, I’m Bryan Yeaton for The Weather Notebook. Insects are cold-blooded animals whose activity and life cycle development are largely controlled by the temperature of their environment. Their development rate increases as the temperature increases above a base temperature and continues until an upper threshold is reached. Such knowledge allows pest management professionals to predict specific events in the insect’s life such as hatching and react accordingly.
To avoid long-term application of pesticides, pest management folks have borrowed a weather tool from agriculturists — the growing-degree day — to help them control these six-legged critters.
The growing-degree day is calculated by first determining the day’s mean temperature: by adding the minimum and maximum temperatures and then dividing by two. From this, we subtract a base temperature appropriate for the particular pest. Usually, this is 50F. If the resulting value is negative, we assume zero because growth is arrested when it is too cold.
Thus, a mean temperature of 65 F, and a baseline temperature of 50 would result in the day’s accumulation of 15 growing degree units. The daily totals of units are then accumulated beginning with a selected date as the season progresses.
For example, gypsy moth eggs will hatch anywhere from late April to late May. But, this event only occurs when 90 to 100 growing degree units have been accumulated. By observing egg-laying and then counting growing degree units, pest managers are able to accurately predict the time of hatching. As a result, they can effectively undertake a program of less costly, more environmentally benign insecticide application.
The concept can also be applied to other cold-blooded pests such as mites and aphids.
Thanks to our contributing writer, meteorologist Keith Heidorn. Check out our past shows online at www.weathernotebook.org. We are a program of the Mount Washington Observatory, funded by Subaru of America.
Today's Links
Understanding Degree-days in Pest Management Decision Making
http://www.ento.vt.edu/Fruitfiles/Understanding_Degree_Days.html
Development of European corn borer
http://bob.soils.wisc.edu/wimnext/corn/euroborer.html
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