Parental photoperiod affects egg diapause in a montane population of Mormon crickets Anabrus simplex (Orthoptera: Tettigoniidae)

Authors: Srygley, Robert

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2020
Publication Date: 6/9/2020
Citation: Srygley, R.B. 2020. Parental photoperiod affects egg diapause in a montane population of Mormon crickets Anabrus simplex (Orthoptera: Tettigoniidae). Environmental Entomology. 49(4):895-901. https://doi.org/10.1093/ee/nvaa062.
DOI: https://doi.org/10.1093/ee/nvaa062

Interpretive Summary: Parental photoperiod affects egg diapause in a montane population of Mormon crickets. Conventionally, Mormon crickets are thought to require a single winter to hatch, but at high elevation (2400 m) in the Bighorn Mountains of Wyoming, a population spends the first winter in the earliest egg stage and completes development the following summer, resulting in a two-year life cycle. ARS Researchers at Sidney, Montana conducted research on whether parental photoperiod serves as a cue to prolong diapause of their offspring. A long day photoperiod (15:9h) corresponds to mid-summer and the peak of the growing season, whereas a short-day (12:12h) indicates the beginning of autumn and the end of the growing season. Although short day females were not more likely to lay eggs that developed in the second summer, they were more likely than long day females to lay eggs with a multi-annual life cycle. This study demonstrates parental control over offspring diapause. Control measures applied to adults in mid-summer will reduce the frequency of eggs in prolonged diapause relative to late summer applications.

Technical Abstract: Insect diapause is a state of arrested development persisting when conditions are favorable for growth. Prolonged diapause, which occurs when diapausing insects remain in diapause for longer than a year, is relatively uncommon. Mormon crickets, which cause substantial loss of rangeland forage and major damage when they migrate into crops, are univoltine with a typical annual life cycle, but at high elevation (2400 m) in the Bighorn Mountains of Wyoming, a population with prolonged diapause spends the first winter in the earliest egg stage, presumably in a biennial life cycle. To test whether parental photoperiod serves as a cue to prolong diapause, mating pairs from the Bighorn Mountains were set in the same standard daily temperature and humidity profiles (30:15°C and 40:30%) with twenty pairs on short daylength (12:12h) and twenty on long daylength (15:9h). Although the population is believed to be biennial, almost every parental pair had some eggs that remained undeveloped after two warm periods. Although females in short daylength were not more likely to have eggs with a biennial life cycle, they were significantly more likely than those in long daylength to lay eggs with a multi-annual life cycle. Parents on short daylength were significantly more likely to lay inviable eggs. Other fitness measures, such as hatchling mass, nymphal survivorship, and adult mass were not significantly different between parental treatments. Diapause termination distributed over multiple years probably constitutes a bet-hedging strategy in an unpredictable environment.