Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2010
Publication Date: 10/20/2010
Citation: Fielding, D.J., Defoliart, L.S. 2010. Embryonic development rates of northern grasshoppers (Orthoptera: Acrididae): implications for climate change and habitat management. Environmental Entomology. 39(5):1643-1651.
Interpretive Summary: Grasshoppers can be major pests of grain crops, but information regarding their life cycle in northern regions is poorly understood or lacking. Temperature dependent rates of egg development were studied to fill these information gaps. Hatching early in the season is important to allow grasshoppers time to mature and reproduce before the end of summer. This suggests that we may be able to prevent grasshopper outbreaks without the use of chemicals by manipulating the vegetation to reduce soil temperatures. Tall, dense stands of vegetation and thick layers of litter shade the soil surface and keep the soil cool. By measuring speed of egg development at a wide range of temperatures, we calculate that if average soil temperature is reduced by 2.5°C, hatching may be delayed by 4 to 9 days, thus limiting population growth. Another reason for studying egg development is to assess the effects of climate change. Currently, grasshopper eggs in the far north take two years to hatch. If temperatures were to increase enough, they may begin hatching after only one year. Our results suggest that predicted increases in summer temperatures will not be enough to cause grasshoppers to switch to a one-year life cycle, although more study of question is needed to make predictions with more confidence.
Technical Abstract: Temperature-dependent rates of embryonic development are a primary determinant of the life cycle of many species of grasshoppers which, in cold climates, spend two winters in the egg stage. Knowledge of embryonic developmental rates is important for an assessment of the effects of climate change and for evaluating strategies of preventing grasshopper outbreaks by habitat management. Increasing temperatures associated with global climate change in the subarctic could potentiate a switch to a univoltine life cycle. On the other hand, 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 and M. sanguinipes. 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 regimes. Actual soil temperatures were recorded at several locations over 4 years. To simulate climate warming, 2.5°C was added to each hourly recorded temperature. To simulate shading, 2.5°C was subtracted. Results suggest that a 2.5°C increase in soil temperatures will result in eggs hatching 4 to 9 d earlier and for prediapause development to advance by about 40%, but may not be enough to promote an annual life cycle, except in the warmest summers. A 2.5°C decrease in temperatures could potentially delay hatch by 4 to 13 d.