Adaptation of the Egg of the Desert Beetle, Microdera punctipennis (Coleoptera: Tenebrionidae), to Arid Environment

Microdera punctipennis Kaszab (Coleoptera: Tenebrionidae) is an endemic species in Guerbantonggut desert in China. To explore the ways that M. punctipennis egg adapts to dry desert environment, morphological characteristics of the egg was investigated along with the egg of the nondesert beetle Tenebrio molitor (Coleoptera: Tenebrionidae). Water loss rate and survival rate of these eggs under different dry treatments (relative humidity0, 10, and 20%) were measured to evaluate the desiccation resistance of the eggs at different developmental stages (day 0, 2, and 5 eggs). Our results showed that the 50-egg weight in T. molitor was heavier than M. punctipennis, while the 50-first-instar larva weight in T. molitor was almost the same as in M. punctipennis. The water loss rate of M. punctipennis egg under dry conditions was significantly lower than T. molitor, and the egg survival rate was significantly higher than T. molitor. The estimated developmental threshold temperature of M. punctipennis egg was 18.30°C, and the critical thermal maximum of M. punctipennis egg is above 39°C. These features partly account for the adaptability of M. punctipennis to desert environment in egg stage.