Voltinism of Odonata: a review

We classified 542 records of voltinism for 275 species and subspecies of Odonata according to three variables: geographical latitude, systematic position and habitat type. We sorted records according to voltinism -categories being three or more generations per year, two generations per year, one generation per year, one generation in two years and one generation in three or more years. We sought to correlate the voltinism of each record with latitude of the study site, thus demonstrating an overall negative correlation between voltinism and latitude. After allowing for phylogenetic similarity a negative correlation remains, although it decreases in strength after removal of taxonomic correlates, mainly between family and genus levels. A negative correlation exists at the species level within most families, with the exception of Lestidae. In genera for which we lacked data for latitudes 0-31 N/S no significant correlation between latitude and voltinism exists. In temporary waters most species complete at least one generation per year; most species in lentic perennial waters complete one generation or fewer; and the majority of species in !otic waters complete half a generation or less. We discuss the roles of exogenous and endogenous factors in influencing voltinism and identify those that may be affecting the correlation that the data reveal. We suggest projects that could improve understanding of voltinism in the context of seasonal regulation and the main types of odonate life cycle so far recognised.