Optimization of a pheromone lure by analyzing the peripheral coding of sex pheromones of Spodoptera frugiperda in China.
BACKGOUND: Sex pheromones of the fall armyworm, Spodoptera frugiperda, show differences in composition and proportions in different geographical populations, but always contain Z9-14:OAc as the major component. Odorant receptor neurons (ORNs) housed in the long trichoid sensilla (TS) of male antennae are essential to detect female-released sex pheromones in moths. RESULTS: In this study, we identified seven components from pheromone gland extracts of female S. frugiperda in the Yunnan population from China, including (Z)-7-dodecen-1-yl acetate (Z7-12:OAc), (Z)-9-tetradecenal (Z9-14:Ald), (Z)-9-dodecen-1-yl acetate (Z9-12:OAc), (Z)-9-tetradecen-1-yl acetate (Z9-14:OAc), (E)-11-tetradecen-1-yl acetate (E11-14:OAc), (Z)-11-tetradecen-1-yl acetate (Z11-14:OAc) and (Z)-11-hexadecen-1-yl acetate (Z11-16:OAc) at a ratio of 1.2:4:0.8:79.1:1.6:1.6:11.7 by gas chromatography coupled with mass spectrometry. Gas chromatography-electroantennographic detection showed that Z9-14:OAc, Z7-12:OAc and Z11-16:OAc are the male antennal active components. Peripheral coding of pheromones in males was investigated by single sensillum recording. Five functional neurons housed in three types of TS were identified based on profiles of neuronal responses, which are responsible for attractive component Z9-14:OAc, synergistic components Z7-12:OAc, Z11-16:OAc, interspecific pheromones (Z)-9-tetradecen-1-ol (Z9-14:OH) and (Z,E)-9,12-tetradecadien-1-yl acetate (Z9,E12-14:OAc), respectively. Wind tunnel and field tests demonstrated that a ternary combination of Z9-14:OAc, Z7-12:OAc and Z11-16:OAc at a ratio of 88:1:11 shows the strongest attractiveness to males. Conclusion: An optimized pheromone blend of Z9-14:OAc, Z7-12:OAc and Z11-16:OAc in an 88:1:11 ratio was identified for monitoring the invasive pest S. frugiperda in China. Five functional ORNs encoding intra- and interspecific pheromones were identified in male antennae, of which three neurons encode attractive component Z9-14:OAc, synergistic components Z7-12:OAc and Z11-16:OAc, respectively, and the other two neurons encode interspecific pheromones Z9-14:OH and Z9,E12-14:OAc, separately.