Effects of parental diet on Mormon cricket egg diapause and embryonic development rate

Authors: Srygley, Robert

Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2024
Publication Date: 7/28/2024
Citation: Srygley, R.B. 2024. Effects of parental diet on Mormon cricket egg diapause and embryonic development rate. Journal of Insect Physiology. 157. Article 104681. https://doi.org/10.1016/j.jinsphys.2024.104681.
DOI: https://doi.org/10.1016/j.jinsphys.2024.104681

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. In this study, the roles of maternal nutrition in determining the length of egg diapause and the rate of egg development were examined. Based on field observations, the prediction was made that a protein restricted diet would result in females laying eggs that had shorter diapause and developed faster. In a ten year study, parental nutrition played a significant role in the duration of egg diapause and development rate, as hypothesized. Contrary to the prediction from field observations, parents with high protein diets laid eggs that diapaused for less time and developed faster. Egg development rate was particularly sensitive to the density of Mormon crickets in which the mother was caged. This suggests that the females respond to the aggregation of Mormon crickets into migratory swarms by laying eggs that develop faster. Hence, the tightm, linear structure of migratory swarms in which females intermittently stop to lay eggs assures that the progeny hatch and develop in dense groups. In this manner, the banding behavior might carry-over into subsequent generations as long as cohorts are dense and protein is available. With band thinning or protein restriction,the progeny remain longer as eggs in the soil and the outbreak subsides. These results provide greater understanding of prolonged diapause and outbreak dynamics in this migratory pest.

Technical Abstract: As a result of its effects on fitness, transgenerational phenotypic modification can alter population demographics and community interactions. For ectotherms, both diet and temperature have important effects on organismal fitness, but they are rarely investigated together. Mormon crickets are capable of diapausing as eggs in the soil for multiple years with duration largely dependent on cumulative heat units or degree days. Because Mormon crickets can be abundant in the landscape in one year and disappear suddenly the next, I asked: does parental nutrition affect the duration of egg diapause? To this end beginning in the ultimate nymphal instar, Mormon crickets were fed a diet high in protein, one equal in protein to carbohydrate, or a diet high in carbohydrates and the time for 50% of the eggs to develop after they were laid was measured. If parental nutrition affects egg diapause, then that change in sensitivity to heat might also alter the relationship between embryonic development rate and temperature. I asked: does parental nutrition affect embryonic development rate as a function of temperature? To this end, I manipulated densities of grasshopper and Mormon cricket nymphs in field cages, collected eggs from the adult Mormon crickets, and measured the optimal temperature, maximum development rate, and thermal breadth for embryonic development of the offspring. I found that Mormon crickets fed a high protein diet laid eggs with shorter diapause. Consistent with this long-term result, those housed with more grasshoppers to eat laid eggs that had a faster maximum development rate, whereas those without grasshoppers laid eggs with slower maximum developmental rates but broader thermal breadth. In addition, Mormon crickets housed with more conspecifics laid eggs with faster development rates, whereas thermal breadth and the temperature optima were not affected by cricket density. As predicted, Mormon cricket diets significantly affected egg diapause and development rates. Contrary to expectations based on field observations, Mormon crickets fed high protein diets laid eggs with significantly shorter egg diapause and significantly faster egg development rates. Interestingly, doubling of Mormon cricket density caused eggs to develop in nearly half the time. This latter result indicates that Mormon cricket aggregations promote rapid development of progeny.