Effects of temperature and moisture on Mormon cricket reproduction with implications for responses to climate change

- For the U.S. Great Basin, an increase in summer temperature (1-3 °C by 2045) and a decrease in precipitation are predicted.
- The proportion of eggs developing was sensitive to small changes (2-4 °C) in ambient, soil, and maternal body temperatures.
- In contrast, the eggs were largely resilient to major changes in soil moisture during summer development.

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% to 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.