Electroantennogram and behavioral responses of Cotesia plutellae to plant volatiles

Plant volatiles have been demonstrated to play an important role in regulating the behavior of Cotesia plutellae, a major larval parasitoid of the diamondback moth (DBM), Plutella xylostella, but little is currently known about the function of each volatile and their mixtures. We selected 13 volatiles of the DBM host plant, a cruciferous vegetable, to study the electroantennogram (EAG) and behavioral responses of C. plutellae. EAG responses to each of the compounds generally increased with concentration. Strong EAG responses were to 100 L/mL of trans-2-hexenal, benzaldehyde, nonanal and cis-3-hexenol, and 10 L/mL of trans-2-hexenal and benzaldehyde with the strongest response provoked by trans-2-hexenal at 100 L/mL. In the Y-tube olfactometer, C. plutellae, was significantly attracted by 1 L/mL of trans-2-hexenal and benzaldehyde. -caryophyllene, cis-3-hexenol or trans-2-hexenal significantly attracted C. plutellae at 10 L/mL, while nonanal, benzyl alcohol, cis-3-hexenol or benzyl cyanide at 100 L/mL significantly attracted C. plutellae. Trans-2-hexenal significantly repelled C. plutellae at 100L/mL. EAG of C. plutellae showed strong responses to all mixtures made of five various compounds with mixtures 3 (trans-2-hexenal, benzaldehyde, nonanal, cis-3-hexenol, benzyl cyanide, farnesene, eucalyptol) and 4 (trans-2-hexenal, benzaldehyde, benzyl alcohol, (R)-(+)-limonene, -ionone, farnesene, eucalyptol) significantly attracting C. plutellae. These findings demonstrate that the behavior of C. plutellae can be affected either by individual compounds or mixtures of plant volatiles, suggesting a potential of using plant volatiles to improve the efficiency of this parasitoid for biocontrol of P. xylostella.