Top-down control and elasticity analysis were conducted on mitochondria isolated from the midgut of the tobacco hornworm (Manduca sexta), to assess how temperature affects oxidative phosphorylation in a eurythermic ectotherm. Oxygen consumption and protonmotive force (measured as membrane potential in the presence of nigericin) were monitored at 15°C, 25°C, and 35°C. State 4 respiration displayed a Q₁₀ of 2.4 to 2.7 when measured over two temperature ranges (15°C to 25°C and 25°C to 35°C). In state 3 the Q₁₀'s for respiration were 2.0 and 1.7 for the lower and higher temperature ranges, respectively. The kinetic responses (oxygen consumption) of the substrate oxidation system, proton leak, and phosphorylation system increased as temperature rose, although the proton leak and substrate oxidation system showed the greatest thermal sensitivity. While there were temperature-induced changes in the activities of the oxidative phosphorylation subsystems there was no change in the state 4 membrane potential and little change in the state 3 membrane potential. Top-down control analysis revealed that control over respiration did not change with temperature. In state 4, control of respiration is shared nearly equally by the proton leak and the substrate oxidation system whereas in state 3 the substrate oxidation system exerted over 90% of the control over respiration. The proton leak and phosphorylation system account for less than 10% of the temperature-induced change in the state 3 respiration rate. Therefore, when the temperature is changed, the state 3 respiration rate is altered primarily because of temperature's effect on the substrate oxidation system.