Effects of crowding, isolation, and transfer from isolation to crowding on total ecdysteroid content of eggs in Schistocerca gregaria.

We examined the ecdysteroid content of eggs from crowd-reared and solitary-reared desert locusts, Schistocerca gregaria, throughout embryogenesis from the day of egg laying until shortly before hatching on day 14. Depending on the time during incubation, ecdysteroid content in eggs from crowd-reared females was 5-10 times higher than in eggs from solitary-reared females. Our investigation revealed two peaks in ecdysteroid content of eggs from crowd-reared females, a small one at day 3 and a major peak at day 10 of incubation. At days 10, 12 and 14 during incubation of eggs from crowd-reared females, we found a positive correlation between egg mass and ecdysteroid content. There was no difference between eggs from the bottom and the top of individual egg pods, but variation in ecdysteroid content between egg pods from different females was considerable in all treatment groups. A brief crowding of solitary-reared females at the time of egg laying, a treatment that initiates maternally mediated gregarization of the developing offspring, had no effect on the consistently low ecdysteroid content in the eggs. This result rules out the possibility that the crowding experience of females is transmitted to the offspring by variation in the total amount of ecdysteroids in their eggs.