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Diapause Traits of Melanoplus sanguinipes and Melanoplus borealis (Orthoptera: Acrididae)

Fielding, D.J.
Annals of the Entomological Society of America 2008 v.101 no.2 pp. 439
Melanoplus sanguinipes, Melanoplus, grasshoppers, embryo (animal), embryogenesis, diapause, cell respiration, respiratory gases, carbon dioxide, cold, duration, egg hatchability, geographical variation, Alaska, Idaho
A thorough understanding of diapause development in insects is needed for prediction of population responses to climate change, for realistic simulation models, and for effective pest management. In Melanoplus sanguinipes F. and Melanoplus 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, 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 4-8 d to levels approximately equal to 70% lower than peak rates of prediapause, late stage embryos, in all populations. In the Idaho population, subjecting prediapause embryos to a cold treatment (5°C) caused the embryo to avert diapause: respiration in these embryos continued to increase after chilling as the embryo developed directly to hatching. In M. borealis and M. sanguinipes from Alaska, chilling of prediapause embryos did not affect subsequent diapause development: respiration rates in these embryos increased until they entered diapause and then declined. About the same amount of time at 5°C was necessary to avert diapause in early stage embryos of the Idaho population as was required to terminate diapause in late stage embryos. Respiration rates of diapausing embryos increased with increasing time spent at 5°C. Respiration continued to increase after transfer to warm temperatures 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 Alaska.