Aestivation and diapause syndromes reduce the water balance requirements for pupae of the Hessian fly, Mayetiola destructor

AbstractWe report the water balance of aestivating (summer), diapausing (winter), and non‐diapausing pupae of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). Maintaining water requirements during pupal dormancy is particularly important because water cannot be replenished actively by drinking. Dehydration tolerance (25% loss before succumbing to dehydration) and water content (63–65%) were not different for the three types of pupae. Differences were noted in the net transpiration rates (NTRs, % body water per hour at 0% r.h.) between dormant (0.24–0.28% per hour) and non‐diapausing (0.47% per hour) pupae 10 days after pupariation, but not between aestivating (0.28% per hour) and diapausing (0.24% per hour) pupae. These reduced NTRs result in extended pupal survival, indicated by adult eclosion, during exposure to dehydrating conditions. Net transpiration rates for aestivating and diapausing pupae were further reduced as dormancy progressed (up to 130 days) until individuals were moved to conditions that break dormancy. Pupae could not take up water from the atmosphere below vapor saturation (100% r.h. or 1.00 av), and rely upon contact with liquid water or moist plant tissue to replenish their water stores. The critical transition temperatures (CTT) of the aestivating and diapausing pupae were significantly higher than those of non‐diapausing pupae, suggesting that modified cuticular lipids are present on aestivating and diapausing pupae. Thus, aestivation and diapause trigger a dormancy specific water balance profile characterized by reduced NTRs and increased CTTs.