Emergence Patterns and Size Variation of Odonata in a Thermal Reservoir

Patterns of odonate emergence were examined seasonally in a reservoir receiving thermal effluents. Exuviae were routinely removed from the interior sides of vertebrate predator exclusion cages. Size, distribution, mean emergence date, and synchronization of emergence were determined for nine species at six stations along a thermal gradient (19.7 to 25.6°C). Mean emergence date varied significantly among species; the earlier emerging species were more synchronous. Temperature influenced the distribution of some of the species investigated. Most species had significant differences in emergence date among stations, and significant size differences among stations were found in three of the nine species. With the exception of the two earliest emerging species, the later in the year the emergence date, the smaller the individual emerging.