Resistance to desiccation and starvation of two species of Brachinus (Coleoptera: Carabidae) from southeastern Arizona

Abstract

Resistance to desiccation and starvation of two species of Brachinus were compared in laboratory studies, and the components of water and energy balance were determined. Brachinus mexicanus, which dominates at temporary ponds far from permanent water, survived desiccation or starvation longer than did B. lateralis, which dominates at permanent ponds. The difference in desiccation resistance was a result of greater tolerance of low body water and greater amount of expendable water in B. mexicanus. Neither rates of water loss nor spiracular control of water loss differed significantly between these two species. Brachinus mexicanus lost mass less rapidly when starved and had a lower resting metabolic rate than did B. lateralis, indicating that greater resistance to starvation was due to lower rate of energy consumption. Both species had similar amounts of stored energy reserves, and there was no evidence of change in metabolic rates due to starvation. Although these differences may be part of the explanation of the scarcity of B. lateralis at some temporary ponds, they do not explain the scarcity of B. mexicanus at permanent ponds.