Prolonged Diapause in Mormon Crickets: Embryonic Responses to Three Measures of Time

Authors: Srygley, Robert

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2024
Publication Date: 4/17/2024
Citation: Srygley, R.B. 2024. Prolonged Diapause in Mormon Crickets: Embryonic Responses to Three Measures of Time. Journal of Insect Physiology. 155:1-7. https://doi.org/10.1016/j.jinsphys.2024.104634.
DOI: https://doi.org/10.1016/j.jinsphys.2024.104634

Interpretive Summary: Information on the timing of pest insect development is beneficial to land managers and surveyors by indicating when insects should be surveyed. It also improves forecasting of population growth. Mormon cricket eggs are unusual in that they can remain in diapause in the soil for multiple years without forming an embryo, and yet nothing is known about the environmental cues for timing of Mormon cricket embryo development. In two high elevation populations from Wyoming and Arizona, I used a laboratory experiment to test whether embryonic development was dependent on the number of annual cycles since the egg was laid, inspired by periodical cicadas, which ‘count’ the number of cycles to synchronize emergence. I also tested whether embryonic development was dependent on the duration of winter chill or the duration of the summer warm period. I conducted the study on 13 sibling groups,each serving as an independent replicate. In no instance did embryonic development depend on the number of annual cycles. For eight replicates, embryonic development of Mormon crickets was dependent on duration of the growing season rather than chill time or number of annual cycles. The duration of the growing season required for 50% of the embryos to develop was well over one year, ranging from 84 to 144 weeks. For one replicate, development was dependent on chill time, and not on the duration of the growing season or number of annual cycles. Hence, more than one cue may be important. The chill time for half the eggs to develop was 60 weeks which is also more than one year. These results provide greater understanding of prolonged diapause in Mormon crickets and will contribute to forecast models of Mormon cricket outbreak dynamics.

Technical Abstract: Mormon cricket eggs can remain diapausing in soil for multiple years without forming an embryo. I investigated whether embryonic development was dependent on the number of annual cycles since the egg was laid, duration of the summer period (forcing), or duration of the winter period (chilling). Male and female Mormon crickets collected in Arizona and Wyoming were paired in the lab. For each mating pair, sibling eggs were incubated 12 weeks, fully developed embryos were removed, and the remaining eggs were split evenly among three treatments: a long cold period and a long warm period; a short cold period and a long warm period; and a short cold period and a short warm period, which respectively completed 2 annual cycles, 3 cycles, and 4 cycles in 60 calendar weeks. In each cycle, developed eggs and eggs that appeared inviable were counted and removed. For each mating pair, I used survival analyses to test for differences in 1) the number of annual cycles, 2) the warm period duration, and 3) the cold period duration required for the embryos to develop. I also measured the median proportion of embryos developing in each cycle and population to see if development was greatest in prime numbered cycles. For nine of 13 mating pairs, one of the three factors was not excluded as a determinant of the phenology of embryonic development. Duration of the growing season was not rejected in eight of 13 cases. Duration of the growing season required for 50% of the eggs to develop ranged from 84 to 144 weeks. In one case from Arizona, the duration of the cold period was the only factor not rejected. Median chill time was 60 weeks, which is also more than one year. Despite this exception, I conclude that duration of the growing season is typically the factor that determines timing of embryonic development for Mormon crickets. For these two high elevation populations, median forcing or chilling exceeded one year.