Gnathiid male adults attract female larvae but are ignored by male larvae

In the gnathiid isopod, Gnathia hayashiae, male adults attract female larvae to mate by releasing sex pheromones. Gnathiid females are thought to mate only once in their lifetime, immediately after metamorphosis. Therefore, this attraction should be an effective adaptation strategy to prevent females from missing mating opportunities. Attraction by adult males is reasonable because larvae are more motile than adults are. In contrast, male adults are potential reproductive competitors for male larvae. How do the male larvae respond to adult males? The present attraction test showed that neither adult male nor adult male extracts provoked a specific reaction in male larvae. In addition, the adult female extracts did not exhibit larval attractant/avoidant activity. We hypothesized that male larvae are not required to avoid male adults, because G. hayashiae adults have low motility and rarely encounter conspecific males in the wild.