Influence of cold temperature and exposure time on egg overwintering survival in the white-whiskered grasshopper (Orthoptera: Acrididae)

Authors: Branson, David - Dave

Submitted to: Journal of Orthoptera Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2019
Publication Date: 5/14/2020
Citation: Branson, D.H. 2020. Influence of cold temperature and exposure time on egg overwintering survival in the white-whiskered grasshopper (Orthoptera: Acrididae). Journal of Orthoptera Research. 29(1):63-65. https://doi.org/10.3897/jor.29.46967.
DOI: https://doi.org/10.3897/jor.29.46967

Interpretive Summary: Cold winter air temperatures and snow cover have been assumed to play an important role in grasshopper overwintering egg survival in northern latitudes in North America, but the exact role cold temperatures have on grasshopper population changes remains poorly understood. ARS researchers in Sidney, Montana conducted an experiment to determine if eggs of the whitewhiskered grasshopper are more vulnerable to temperature extremes due to their shallow depth or if selection for cold hardiness has reduced vulnerability to temperature extremes. The eggs of several grasshopper species laying egg pods at a range of depths below the soil surface in North America appear to die at fairly similar cold temperatures, indicating that extremely cold sustained temperatures are required to significantly reduce grasshopper egg survival. Subsurface temperatures were found to be colder at the depth of whitewhiskered grasshopper egg pods than at the depth of many grasshopper species that lay vertically oriented egg pods, during a cold winter period when snow and litter were removed from the soil surface. Due to its shallow egg pod location, the whitewhiskered grasshopper may have an increased vulnerability to cold temperature events when snow cover is limited that could contribute to its northern distribution boundary. The results can be used to predict grasshopper declines in the year following severely cold winter temperatures.

Technical Abstract: We examined the effects of cold temperatures and exposure time on egg survival and hatching success of the whitewhiskered grasshopper, Ageneotettix deorum. Temperature treatments ranged from 4°C to -35°C, with treatment times ranging from 48 to 240 hours. Both decreasing temperatures and time at temperature negatively affected egg survival, with a lethal temperature below -25°C. Given the similar lethal temperatures among several North American grasshopper species, the relatively shallow location of A. deorum egg pods would result in increased vulnerability to egg mortality from cold temperatures in the absence of snow.