THERMOREGULATION BY ENDOGENOUS HEAT-PRODUCTION IN 2 SOUTH-AMERICAN GRASS DWELLING CICADAS (HOMOPTERA, CICADIDAE, PROARNA)

Proarna bergi (Distant) and Proanza insignis Distant use metabolic hea t to raise body temperature (T-b) for activity when ambient conditions would prevent activity in ectothermic animals. Both species were obse rved singing during overcast or rainy conditions and at dusk. T(b)s in the field exceeded ambient by as much as 7.4 degrees C when solar rad iation was unavailable to the insects. In the laboratory voluntary met abolic heat production raised T-b as much as 12.3 degrees C and 10.7 d egrees C above ambient in P. bergi and P. insignis respectively. Estim ates of metabolic rate from heating and cooling curves were 0.118 ml O -2 per min for P. bergi and 0.126 ml O-2 per min for P. insignis. Fine shiver-like movements of the thoracic musculature produced the heat. The T-b at which endogenous warm-up voluntarily stopped in the laborat ory was similar to the T(b)s measured in active animals in the field. Thermal responses measured in the laboratory also illustrate these ani mals are thermoregulating with endogenous heat. Endogenous heat produc tion uncoupled reproductive behavior from environmental constraints.