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item Fielding, Dennis
item Defoliart, Linda

Submitted to: Journal of Orthoptera Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2005
Publication Date: 12/30/2005
Citation: Fielding, D.J., Defoliart, L.S. 2005. Density and temperature-dependent melanization of fifth-instar Melanoplus sanguinipes: interpopulation comparisons. Journal of Orthoptera Research. Vol. 14(1): 107-113

Interpretive Summary: Basking in sunlight to raise internal body temperatures above ambient is a very common behavior in grasshoppers. Elevated body temperature has many benefits for grasshoppers: faster feeding and growth rates, and enhanced disease resistance. Darker grasshoppers will absorb more solar energy and, hence be able to more efficiently raise body temperatures compared to lighter colored grasshoppers. We found that grasshoppers from Alaska tended to be darker than those of the same species from Idaho. Grasshoppers also tended to be darker when they have experienced cooler temperatures and crowded conditions over their lifetime. By more efficiently capturing solar energy, northern populations of grasshoppers are able to thrive in the short growing seasons of the subarctic. These results will help us to better predict the effects of pathogenic biocontrol agents and grasshopper population growth.

Technical Abstract: Behavioral thermoregulation, by basking in sunlight, is very common in acridids. The resulting increased body temperatures may be beneficial by accelerating feeding and developmental rates and by enhancing disease resistance. The absorption of solar energy is affected by the degree of cuticular melanization. In this paper, we quantify differences in color and thermoregulation between subarctic and temperate populations of Melanoplus sanguinipes. We also quantify effects of rearing temperatures and density on melanization of 5th instars. Alaskan grasshoppers tended to be darker than those from Idaho when reared under the same conditions and Alaskan grasshoppers also responded to cooler rearing temperatures by increased pigmentation. The Idaho population responded more strongly to density effects than the Alaskan grasshoppers, at least at the temperature at which the density experiment was conducted. Increased pigmentation was demonstrated to enhance the ability to thermoregulate. Absorption of wavelengths in the near infrared region was similar to that in the visible range, confirming that color is a reliable measure of relative absorption of total solar irradiance. Strong selection for efficient thermoregulation at high latitudes was suggested by the population differences in pigmentation.