Embryonic developmental rates of northern grasshoppers (Orthoptera: Acrididae): implications for climate change and habitat management

Accurate models of temperature-dependent embryonic developmental rates are important to assess the effects of a changing climate on insect life cycles and to suggest methods of population management by habitat manipulation. Embryonic development determines the life cycle of many species of grasshoppers, which, in cold climates, spend two winters in the egg stage. Increasing temperatures associated with climate change in the subarctic could potentiate a switch to a univoltine life cycle. However, egg hatch could be delayed by maintaining a closed vegetative canopy, which would lower soil temperatures by shading the soil surface. Prediapause and postdiapause embryonic developmental rates were measured in the laboratory over a wide range of temperatures for Melanoplus borealis Fieber and Melanoplus sanguinipes F. (Orthoptera: Acrididae) A model was fit to the data and used to predict dates of egg hatch in the spring and prediapause development in the fall under different temperature regimens. Actual soil temperatures were recorded at several locations over 5 yr. To simulate climate warming, 2, 3, or 4°C was added to each hourly recorded temperature. Results suggest that a 2, 3, or 4°C increase in soil temperatures will result in eggs hatching ≈ 3, 5, or 7 d earlier, respectively. An increase of 3°C would be required to advance prediapause development enough to allow for a portion of the population to be univoltine in warmer years. To simulate shading, 2 and 4°C were subtracted from observed temperatures. A 4°C decrease in temperatures could potentially delay hatch by 8 d.