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Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/1/2014 Publication Date: 5/14/2014 Publication URL: http://handle.nal.usda.gov/10113/58900 Citation: Srygley, R.B. 2014. Effects of temperature and moisture on Mormon cricket reproduction with implications for responses to climate change. Journal of Insect Physiology. 65:57-62. DOI: 10.1016/j.jinsphys.2014.05.005. Interpretive Summary: During the last decade, the sudden increase in densities of flightless Mormon crickets over vast areas of the western United States suggests that climate is an important cause of outbreaks. Warmer, drier summers are predicted for most of the Great Basin, and yet little is known about the response of Mormon crickets to changes in temperature and soil moisture. In a laboratory setting, we attempted to match daily cycles in light and temperature as close to field conditions as possible and compare those conditions to our standard practice of a 30°C daytime temperature under fluorescent lighting. We found that very small changes in temperature had large effects on reproduction, and we interpret this finding as an effect of maternal body temperature on the propensity to lay fully developed eggs. Reproduction was greatest when maternal body temperature reached 35°C during the daily cycle, whereas it dropped off dramatically when it only reached 30°C or exceeded 37°C. We applied a single pulse of moisture to the soil within the first two weeks that the eggs were laid and allowed the soil to dry over the 70 days required for development. Fewer embryos developed when soil was dry or initially saturated with moisture, but more of the developed embryos hatched the following spring when they had lacked summer soil moisture. As a result, the eggs were largely resistant to summer drought. The effects of temperature and moisture on development and hatching of Mormon cricket nymphs are essential components of predictive models for population responses to climate. This understanding also helps develop a best practice for rearing Mormon crickets in a lab setting. Technical Abstract: During the last decade, populations of flightless Mormon crickets Anabrus simplex (Orthoptera: Tettigoniidae) increased suddenly over vast areas of the western United States, suggesting that climate is an important factor driving outbreaks. Moreover summer temperatures are predicted to increase and precipitation is expected to decrease in most areas of the U.S. Great Basin, but little is known of the response of Mormon crickets to changes in temperature and soil moisture. In a laboratory study, we varied ambient temperature and lighting and measured the propensity of mating pairs to mate, and the proportion of eggs that developed into embryos. We found that reproduction was optimal when ambient temperature reached 30°C and the insects were beneath broad-spectrum lights such that maternal body and soil temperatures reached 35°C. Fewer eggs that developed fully were laid when maternal body and soil temperatures reached 30°C or 37-39°C. We also varied initial soil moisture from 0-100% saturated and found that more eggs reached embryonic diapause when initial soil moisture was 25 or 50% of saturated volume. However more of the developed eggs hatched when treated in summer soils with 0-25% of saturated moisture. We conclude that small changes in temperature had large effects on reproduction, whereas large changes in moisture had very small effects on reproduction. This is the first report of Mormon crickets mating in a laboratory setting and laying eggs that hatched, facilitating further research on the role of maternal and embryonic environments in changes in population size. |
