Separating the sexes: Sexual dimorphism in the genus Coccinella and the implications for conservation research

Several native ladybug species from the genus Coccinella have declined dramatically in the U.S. over the past two decades. A number of hypotheses have been proposed but research has been slow due to various limitations. One hypothesis involves mating ecology but a quick and accurate method of sexing live specimens has not been available. Ladybugs typically do not show exaggerated sexual dimorphisms and the only reliable sexing methods for some species have been dissection and behavioral observations. Behavioral methods can potentially lead to sex identification but are time consuming, require exposing naïve individuals to conspecifics, and risk incorrect identification since homosexual mounting in these species has been observed in the lab. Closer examination of the species Coccinella novemnotata, Coccinella septempunctata, Coccinella transversoguttata, and Coccinella trifasciata has led to the discovery of a reliable and efficient way to differentiate the sexes by looking at the shape of the fifth visible sternite and this method has proven to be 100% reliable for all four species. Another, even more rapid, method uses the shape of a prominent pronotum marking and shows promise for C. novemnotata but is not consistent across all four species. In this presentation I will share morphometric data that quantify these dimorphisms and provide evidence for the reliability of these methods. Additionally, I will outline the significance of this discovery for research into the ecology of these species and the potential for illuminating the causes of the sudden disappearance of threatened Coccinella species in the United States.