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

Summary

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 (T_th) within fairly narrow limits by utilizing behavioral mechanisms and evaporative cooling. However, syntopic populations of these two species were found to regulate at different T_th despite having synchronous annual and daily activity periods; overall mean T_th 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 T_th. Part of the difference in T_th resulted from the fact that individuals of the two species were active in thermally distinct microhabitats. Within each species, mean T_th varied among behavior categories, and differences in how the two species allocated their time between activities also contributed to the interspecific difference in T_th. 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 T_th 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 T_th on ambient temperature (T_am) 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.