Thermoregulation and activity patterns of two syntopic cicadas, Tibicen chiricahua and T. duryi (Homoptera: Cicadidae), in central New Mexico.

Tibicen chiricahua and T. duryi are cicada species that are active as adults early each summer in central New Mexico, and are often syntopic in pinyon-juniper woodlands. Both species regulate thoracic temperature (Tth) within fairly narrow limits by utilizing behavioral mechanisms and evaporative cooling. However, syntopic populations of these two species were found to regulate at different Tth despite having synchronous annual and daily activity periods; overall mean Tth of T. chiricahua was 3.1°C higher than it was for T. duryi. Interspecific differences in evaporative cooling abilities and rates of passive heat exchange could not account for this difference in Tth. Part of the difference in Tth resulted from the fact that individuals of the two species were active in thermally distinct microhabitats. Within each species, mean Tth varied among behavior categories, and differences in how the two species allocated their time between activities also contributed to the interspecific difference in Tth. Though T. duryi is restricted to pinyon-juniper habitats such as the one in this study, T. chiricahua is also found in warmer habitats. The difference in Tth in the syntopic populations probably reflects interspecific differences in thermal preferences and thermal optima that are adaptive over their respective habitat ranges. The degree of dependence of Tth on ambient temperature (Tam) varied between activities within both species, with the least dependence exhibited during singing. Singing involves intense activity of tymbal muscles, which apparently can only function effectively over a relatively narrow range of temperature.