Data from: Effects of Parental Diet on Mormon cricket Egg Diapause and Embryonic Development Rate

With these data, I evaluated whether the diet of Mormon cricket parents affected the diapause and development rate of the eggs that they laid. This was completed with two lab experiments. The first was a ten year experiment conducted at the ARS Northern Plains Agricultural Laboratory in Sidney Montana on a population from Utah (UT, 38.4249 N, 112.8618 W, 1853 m above sea level). Eggs were laid in the lab by males and females collected from the field, and hatched F1 nymphs were fed natural diet until they molted to 7^th instar when they were sexed and randomly assigned one of three diet treatments. We prepared diets consisting of 42% macronutrients (protein P and carbohydrates C, in select ratios of P:C), 54% cellulose, 1.8% Wesson’s salt mixture, and 2.2% vitamins, linoleic acid, and cholesterol. We gave each insect one of three diet treatments: 2:1, 1:1, and 1:2 P:C (which we label hi P, PC, and hi C, respectively). They were given this diet until they were 9 day old adults. On June 3, 2013, three females of each diet treatment were paired with males of the same diet treatment (e.g., hi C females were paired with hi C males) and each pair of adults was placed in a nylon cage with a pan of dry sand to mate and lay eggs.

The F2 eggs were collected on July 26, 2013, placed in 25% moistened sand (as above) in a cup marked with the parentage and covered with a lid. One PC female died shortly after being placed in the mating cage and had no eggs; the other mating pairs were alive when the eggs were collected. We placed the eggs in a seasonal temperature program which is best described as 6 weeks of winter, 2 weeks of spring, 10 weeks of summer, and 2 weeks of autumn. The temperature program is then repeated. Eggs were screened for development in the final two weeks of each cycle (the autumn period), and the developed eggs were separated from the undeveloped eggs. Half-developed eggs were also separated from the undeveloped eggs to follow the completion of their development separately. For each egg in the sibling group, we tracked the timing of the fate of each egg: either fully developed (and thus ready to enter winter and hatch the following spring), discard (due to being flat, black, or invaded by fungus), broken, or missing. For some mating pairs, we also collected a few eggs and fixed them, which killed the eggs, but cleared the chorion so that we could review their developmental stages (fate=fixed). The temperature treatments were applied for approximately 10 calendar years starting in 2013 when the eggs were collected and ending in April 2024.

The second experiment was conducted at the ARS Northern Plains Agricultural Laboratory in Sidney Montana on a population from Wyoming (WY, 44.8264 N, 107.8280 W, 2773 m a.s.l). To vary maternal diets for this study, Mormon crickets were caged with or without Northern grasshoppers (Melanoplus borealis) in thirty-two 1 m² cages on a mountain meadow on Forest Service Road 14 (FSR 14), Bighorn County, Wyoming (location given above). Northern grasshopper 3^rd and a few 4^th instar nymphs were collected from FSR 14 and placed into cages on June 29, 2018 at densities of 0, 9, 18, and 27 grasshoppers m^-2. In order to examine the effects of Mormon cricket density, an equal number of male and female Mormon cricket nymphs (2^nd or 3^rd instars) were added to the cages on FSR 14 on July 1 at combined densities of 6 and 12 m^-2. The thirty-two cages amounted to four replicates of each grasshopper x Mormon cricket density treatment. Adult Mormon crickets were collected from the cages on August 28, 2018 and transported to the insect rearing facility in Sidney, Montana.

To measure development rate as a function of temperature, I aimed to collect five eggs per treatment temperature from 15 mating pairs. Eggs oviposited in the previous 24 h were sifted from the sand and placed in a petri dish with filter paper moistened with water, covered with a lid, and sealed with parafilm. Twelve females oviposited enough eggs to fill all eight temperature treatments (averaging 4.6 eggs per treatment temperature); three females only had enough to fill five or six of the temperature treatments. For each mating pair, eight petri dishes were marked to indicate the source mating pair, date set up, and one of eight treatment temperatures (T_mean): 22:14°C (T_mean=18°C), 24:16°C (T_mean=20°C), 26:18°C (T_mean=22°C), 28:20°C (24°C), 30:22°C (26°C), 32:24°C (28°C), 34:26°C (30°C), and 36:28°C (32°C). Each of eight incubators cycled between 12 h warm and 12 h cool about its T_mean in continuous darkness. Initially, development of embryos was scored every three to four days beginning at day 34 from when the eggs were laid. The developing eyespot was the first embryonic tissue visible with aid of a dissecting scope. Eggs were given six months to show signs of development. None of the eggs at the lowest temperature (22:14°C) showed any development, and so I placed the same petri dishes of eggs in 38:30°C (T_mean=34°C) to measure development at this ninth experimental temperature with the explicit assumption that exposure to the cold temperature for six months did not affect development rate in this high temperature treatment. Development rate is the inverse of time in days from when the eggs were oviposited to Stage 19 when the cricket fills half of the egg. Relatively few embryos grew to stage 23 due to aestivation at high temperatures.