Author
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Fielding, Dennis |
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Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/10/2004 Publication Date: 12/20/2004 Citation: Fielding, D.J. 2004. Developmental time of Melanoplus sanguinipes f. (Orthoptera: Acrididae) at high latitudes. Environmental Entomology. Vol. 33(6): 1513-1522 Interpretive Summary: It is important to be able to predict the time required for insect pests to develop from eggs to reproducing adults so that control measures can be timed correctly, realistic simulation models can be developed, and to predict the effects of climate change. Temperature is the primary factor driving growth rates in insects. The lesser migratory grasshopper, Melanoplus sanguinipes F., has a very wide geographical range, including subarctic regions where it is a sporadic, but potentially very damaging, pest of small-grain and vegetable crops. This species of grasshopper must overwinter as eggs, and the short summers at high latitudes allow only a limited amount of time for nymphs to complete development, and adults to reproduce. This study was undertaken to determine the tactics grasshoppers use to enable them to thrive in subarctic regions. I found that by using solar energy to increase their body temperatures, these grasshoppers were able to cut the time required to grow from eggs to adults to half of what it would be if they remained at air temperature. There was also some indication that northern populations had intrinsically faster growth rates than populations from warmer climates. These results help us to understand how insects adapt to cool climates, predict the potential geographic ranges of invasive insect pests, and predict effects of climate change. Technical Abstract: Rates of nymphal development of Melanoplus sanguinipes F. from Alaska were determined at 8 constant temperatures between 21 and 42 oC. Diurnally alternating temperatures were used to estimate rates of development at temperatures too low for nymphs to complete development under constant temperatures. A non-linear equation was fit to these data and tested against observed development times in two fluctuating temperature regimes in growth chambers, and two seasons of field sampling. The effect of behavioral thermoregulation on nymphal developmental times in the field was estimated using standard air temperatures and solar-adjusted temperatures. Elevation of body temperature of grasshoppers above ambient temperatures in the field was modeled as a linear function of solar irradiance. Rates of development in the laboratory were higher than previously published data for M. sanguinipes. Estimates using air temperatures only were about half those using solar-adjusted temperatures. Observed developmental times in the field were 45 and 42 days in 2000 and 2002, respectively, similar to times reported from warmer climates. Because of local adaptation and behavioral thermoregulation, duration of nymphal stages in M. sanguinipes is relatively independent of latitude. |
