Electrophysiological and behavioural responses of chestnut moths, Cydia fagiglandana and C. splendana (Lep., Tortricidae), to sex attractants and odours of host plants
Authors: Den Otter C. J. , De Cristofaro A. , Voskamp K. E. , Rotundo G. 
Published: August 2009

Abstract: EAG recordings were made from both males and females of Cydia fagiglandana (Zell.) and C. splendana (Hb.) on stimulation with the tortricid sex attractants (E,E)‐8,10‐dodecadien‐l‐yl acetate (E8E10‐12:Ac), (E,E)‐8,10‐dodecadien‐l‐ol (E8E10‐12:OH) and (Z)‐8‐dodecen‐l‐yl acetate (Z8‐12:Ac). The dose‐response curves of the various attractants were almost identical for males of both species. The order of increasing EAG sensitivity was E8E10‐12:OH < Z8‐12:Ac < E8E10‐12:Ac. In females, EAGs increased in the order E8E10‐12OH < E8E10‐12:Ac < Z8‐12:Ac. They were much less sensitive to the sex attractants; the EAG amplitudes to E8E10‐12:Ac were 20–50 times smaller than those of males. The antennae of C. fagiglandana females were about twice more responsive to the sex attractants than those of females of C. splendana. Recordings from single antennal olfactory cells of C. fagiglandana males showed responses of 1 or 2 cells on stimulation with the sex attractants and with volatiles from chestnut leaves.

The diel spontaneous locomotor activities of both species as measured in actographs ran almost concurrently. Most moths were active during the first 4–6 h and the last 2.5 h of the night. During the day the moths were inactive, except females of C. splendana which already showed some activity at the end of the afternoon. A correlation appeared to exist between the locomotor activities and behavioural responsiveness to attractive odours.

Behavioural responses of males and females were studied in a wind‐tube in the presence and the absence of an airstream. Female calling behaviour was observed. Results suggested that E8E10‐12:Ac is a main component of the female sex pheromone of both Cydia species.

A stream of air, whether or not loaded with attractants, always induced antennal elevation and grooming of the antennae and palps in both males and females. Responses to upwind attractants only occurred after switching off the airstream. It is proposed that either (1) attractive odours in combination with an airstream may evoke an ‘internal excitatory state’ that finds active expression in standing air or that (2) intermittent stimulation with odours, which may occur in the unsteady air shortly after switching off the airflow, is indispensable for inducing upwind displacement.

Branches of chestnut attracted both sexes and functioned as arrestants. Contrary to what was found in several other moth species, signals from the host plant did not appear to induce pheromone production. Males as well as females were attracted to E8E10‐12:Ac, to calling conspecific females and to the smear of abdomen tips cut off from calling conspecific females. With a paper loaded with E8E10‐12:Ac and three conspecific females present in the tube, the females lined up about 20 cm from each other and started to call. These results suggested that sensitivity of the females to their own sex attractants may permit them to detect the presence of other calling females, leading to settling and synchronization of pheromone production, and avoidance of pheromone‐releasing females. As a result, calling females may evenly distribute over the environment.