Author
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FIELDING, DENNIS |
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Submitted to: Annals of the Entomological Society of America
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/13/2007 Publication Date: 3/20/2008 Citation: Fielding, D.J. 2008. Diapause traits in Melanoplus sanguinipes and M. borealis (Orthoptera: Acrididae). Annals of the Entomological Society of America. 101:439-448. Interpretive Summary: Effective insect pest management relies on a thorough understanding of the insect’s seasonal development. Also, prediction of the effects of climate change on insect pests depends on knowledge of the pests adaptations to climate. Most species of North American grasshoppers diapause, which is an interruption of normal development, in the egg stage. Once the embryo begins diapause, a period of cool temperatures, such as the egg would experience over winter, is necessary before normal development resumes and the egg can hatch. Diapause is the primary means for grasshoppers to time their hatching to coincide with favorable seasons for growth and reproduction. I found that diapause in the migratory grasshopper from Idaho differed from that of the same species from Alaska. When eggs from Idaho were chilled at early stages of development, they skipped diapause later and continued normal development to hatching, whereas those from Alaska, if chilled at early stages of development, still entered diapause later and would not hatch unless chilled a second time. Because of the short growing season in Alaska, eggs take two years to hatch. If they skipped diapause after overwintering the first year, they would hatch too late in the season to mature and reproduce before freezing temperatures. This information will help us to predict if and when Alaskan grasshoppers will switch from one generation every two years, to one generation per year, as global warming increases length of the growing season in the subarctic. Technical Abstract: A thorough understanding of diapause is needed for prediction of population responses to climate change, for realistic simulation models, and for the development of effective pest management. In Melanoplus sanguinipes (Fabricius) and M. borealis (Fieber) (Orthoptera: Acrididae), diapause typically occurs in embryos at a late-stage of development. Experiments were conducted to compare diapause traits in two populations of M. sanguinipes, one from Alaska, and one from Idaho, USA, and also in a population of M. borealis from Alaska. Respiration was measured at different stages of embryonic development. As the embryos entered diapause, respiration rates declined over a period of 4 to 8 days to levels about 70% lower than non-diapausing, late-stage embryos, in all populations. After pre-diapause embryos were subjected to a cold treatment (5oC), respiration returned to rates similar to that before chilling, and then began increasing as the embryo continued to grow. In the Idaho population, respiration rates continued increasing as the embryo developed directly to hatching, skipping diapause. In the northern populations, respiration rates increased until embryos reached the diapause stage and then declined. About the same amount of time at 5oC was necessary to avert diapause in early-stage embryos as it was to terminate diapause in late-stage embryos of the population from Idaho. Respiration rates in diapausing embryos increased with increasing time at 5oC, after returning to 22oC. Respiration continued to increase in those that had completed diapause, but in those that had not, respiration soon declined back to diapause levels. In general, there was less flexibility in the diapause program among grasshoppers from the subarctic region. |
