Sex pheromones from male forewings of the Common Grass Yellow Eurema mandarina

The common grass yellow Eurema mandarina has a characteristic patch (sex brand) composed of specialized scales (androconia) and wing intermembranous cells on the ventral surface of its male forewing. This structure is specific to males and is thought to release compounds that induce female mate acceptance. However, no study has demonstrated that these compounds function as sex pheromones in the genus Eurema. Here we report the identification of sex pheromones in males of E. mandarina. Chemical analyses revealed that 6,10,14-trimethylpentadecan-2-one (TMP) and (E/Z)-3,7,11,15-tetramethylhexadec-2-enal [(E/Z)-phytal] were male-specific and abundant in particular regions of the male forewings. TMP was highest in the sex brand, whereas (E/Z)-phytal was concentrated in the anal cell (cell 2 A), lacking androconia and intermembranous cells. The content of these compounds increases with age in males after emergence. In bioassays, virgin females displayed a posture of bending their abdomens as mating acceptance in response to stimulation by fresh male forewings. However, solvent-washed male wings did not induce such female responses, suggesting that some compounds from male wings serve as triggers. When we examined female responses to compounds applied to solvent-washed male wings, authentic TMP and (E/Z)-phytal alone showed little activity. However, the mixture elicited abdomen-bending responses in one-third of the females. Therefore, TMP and (E/Z)-phytal were found to act synergistically as aphrodisiac sex pheromones for E. mandarina females, although these activities were weak.