Mormon cricket eggs can remain in soil for multiple years without forming an embryo. Because periodical cicadas emerge synchronously on prime numbers of years to both avoid and swamp predators, I asked: Do Mormon crickets develop in response to the number of annual cycles resulting in synchronous outbreaks? Male and female Mormon crickets collected in Arizona, Utah, and Wyoming were paired in the lab. For each mating pair, eggs were incubated 12 weeks. Fully developed embryos were removed, and the remaining eggs were split evenly among three treatments: a long winter and a long warm period; a short winter and a long warm period; and a short winter and a short warm period, which respectively completed 2 annual cycles, 3 cycles, and 4 cycles in 60 calendar weeks. 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 winter 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.
Results/Conclusions
For 17 of 27 mating pairs, at least 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 13 of 17 cases, and I conclude that it is a factor that determines embryonic development. This seems reasonable given the importance of growing degree days in insect development. However there were three mating pairs, one from each population, for which the number of cycles was also a potential factor, and for one Utah mating pair, it was the only factor not rejected. In addition, there was one case from Arizona and two from Wyoming for which winter duration was the only factor. The duration of the growing season required for 50% of the Utah eggs to develop was longer than that for Wyoming or Arizona (170 versus 115 weeks). Nevertheless, prime numbers of annual cycles might still be an important factor synchronizing embryonic development and hatching. The most rapid change in the median number of eggs developing occurred at 6-7 cycles for the Arizona population, 9-10 for Wyoming, and 13-14 for Utah, which lie on or near the prime numbers 7, 11, and 13, respectively.