Metal accumulation and loss by Crocothemis servilia (Drury) in a small lake in Shillong, northeastern India (Anisoptera: Libellulidae)

Concentrations and body burdens of copper, cadmium, lead, manganese, zinc, and calcium were measured in the larva and imago. Metal concentrations were greatly affected by size, with the smaller larvae generally having higher concentrations of all metals except copper. Metal body burdens and size, in contrast, were positively correlated. When metal concentrations in different larval size-classes were analyzed, copper levels were not found to exhibit significant changes with increasing weight, while calcium and zinc concentrations levelled off beyond a certain weight. Cadmium, lead, and manganese concentrations, on the other hand, registered steady declines with increasing weight. The body burdens of copper, calcium and zinc increased consistently with increasing weight, while those of cadmium, lead and manganese declined after an initial increase. The concentrations and body burdens of all metals were higher in the final instar larva when compared to those in the adult, except that calcium concentration was higher in the latter. During the final moult, higher proportions of cadmium, lead and manganese were lost along with the exoskeleton than those of copper, calcium and zinc. Thus, the exoskeleton of C. servilia might play an important role in sequestration and eventual elimination of excess metals, particularly the non-essential ones.