Sex, males, and hermaphrodites in the scale insectIcerya purchasi

Androdioecy (the coexistence of males and hermaphrodites) is a rare mating system for which the evolutionary dynamics are poorly understood. Here we study the only presumed case of androdioecy in insects, found in the cottony cushion scale, Icerya purchasi . In this species, female-like hermaphrodites have been shown to produce sperm and self-fertilize. However, rare males are sometimes observed too. In a large population-genetic analysis, we show for the first time that although self-fertilization appears to be the primary mode of reproduction, rare outbreeding events between males and hermaphrodites do occur, and we thereby confirm androdioecy as the mating system of I. purchasi . Thus, this insect appears to have the colonization advantages of a selfing organism while also benefitting from periodic reintroduction of genetic variation through outbreeding with males.