Electrophysiological and Behavioural Responses of Sweetpotato Weevil, Cylas formicarius to Green Leaf Volatiles and Terpenoids

The key to modifying the behaviour of sweetpotato weevil (SPW) Cylas formicarius Fab. lies in understanding the olfactory receptor system and its response to various host plant volatiles produced by sweetpotato. Green leaf volatiles and aromatic terpenoids have been used to study the olfactory receptor depolarization, recovery time from action potential and the rate of response in male and female C. formicarius using electroantennography. Among the 12 compounds tested, cis-3-hexen-1-ol elicited consistently high action potentials in both genders, indicative of hyperpolarization of olfactory receptors. Highest axonal action potentials were elicited by α-humulene, sabinene, (-)-trans-caryophyllene, cis-3- hexen-1-ol and cis-3-hexenal from female antennal receptors compared to those of males (P < 0.01). The rate of response was found to be higher in females than male weevils to each of the compounds. Cis-3- hexen-1-ol which produced highest amplitude (depolarization), was observed to have attracted the least number of weevils. Cis-3-hexen-1-ol, cis-3-hexenal and α-humulene attracted much fewer females in dual choice olfactometer tests, indicating that these compounds act as repellents to both male and female SPWs. Except ocimene, ylang-ylang oil and cis-3-hexenyl acetate, all the nine compounds acted as repellents to SPW in olfactometer bioassays.