Behavioural and electrophysiological activity of unsaturated analogues of the pheromone tetradecyl acetate in the small ermine moth Yponomeuta rorellus

Abstract

In field‐trapping experiments the unsaturated analogues (E)‐6‐, (E)‐12‐, and (Z)‐12‐tetradecenyl acetate were as attractive to male Yponomeuta rorellus Latr. as the native pheromone component tetradecyl acetate. All four analogues attracted more males than virgin females did, whereas (Z)‐6‐, (E)‐11‐, (Z)‐10‐ and (Z)‐11‐tetradecenyl acetate were essentially non‐attractive. Addition of 1–30% of (Z)‐11‐tetradecenyl acetate to the pheromone tetradecyl acetate reduced the attraction to less than 2%. Flight tunnel experiments with Y. rorellus confirmed the activity of the (E)‐6‐ and (E)‐12‐tetradecenyl acetates and demonstrated the activity of (E)‐7‐tetradecenyl acetate as well. These analogues elicited orientation behaviour, upwind flight and landing at the odour source as frequently as the native pheromone did. Single sensillum recordings from male Y. rorellus showed two types of cells in most sensilla. A large spike amplitude cell was stimulated by tetradecyl acetate and the unsaturated analogues (E)‐11‐, (E)‐6‐ and (E)‐12‐tetradecenyl acetate, and to a lower extent by the (Z)‐6‐, (Z)‐11‐ and (Z)‐12‐isomers. A cell with medium spike amplitude was stimulated by (Z)‐9‐tetradecenyl and (Z)‐11‐hexadecenyl acetate. Some sensilla contained a third cell firing with a small spike amplitude which was activated by (Z)‐11‐tetradecenol. Thus the tetradecyl acetate receptor was stimulated not only by the behaviourally active analogues, but also by behavioural antagonists. The interaction of (E)‐11‐tetra‐decenyl acetate and tetradecyl acetate with the same antennal receptor cell was also demonstrated in Y.cagnagellus. Electrophysiological discrimination between behavioural attractants and antagonists and the role of behavioural antagonists in the interspecific relations between Y.rorellus and sympatric closely related species are discussed.

Mechanism for saltational shifts in pheromone communication systems

“…Male Y. rorellus antennae do have an abundance of receptor neurons that are stimulated by tetradecyl acetate (21). What sets this particular type of neuron apart from the typical lepidopteran sex pheromone receptor neuron, however, is that it is at least as responsive to the (E)-and (Z)-11-tetradecenyl acetate molecules emitted by other sympatric Yponomeuta species as to its own saturated tetradecyl acetate pheromone (21).…”

“…The activity of this neuron has been conjectured to be the factor preventing these two compounds from attracting Y. rorellus males despite the ability of these compounds to excite the tetradecyl acetate pheromone receptor neuron (21). Neither (Z)-nor (E)-12-tetradecenyl acetate activates the antagonistic neuron, but, as mentioned, both compounds do excite the tetradecyl acetate pheromone receptor neuron.…”

“…Although it has been uncommon to find even a slightly broadly tuned pheromonecomponent receptor neuron in moths, the few examples that do exist are instructive and thus far seem to coincide with apparent major chain-shortening or desaturation-enzyme-related alterations in species' pheromone emissions (17)(18)(19)(20)(21). A good example comes from extensive research on the European ermine moth species complex, genus Yponomeuta (3,17).…”

“…There are, however, examples of attraction to pheromone blends of other species being impaired by the excitation of antagonistic neurons. These neurons seem to function solely for detecting components emitted by nonconspecific females and to thus stop males from f lying upwind to these blends (2,3,18,19,21). Such behavioral antagonist neurons typically exhibit relatively broad response spectra to a variety of pheromone-related molecules (18).…”

“…Male Y. rorellus antennae do have an abundance of receptor neurons that are stimulated by tetradecyl acetate (21). What sets this particular type of neuron apart from the typical lepidopteran sex pheromone receptor neuron, however, is that it is at least as responsive to the (E)-and (Z)-11-tetradecenyl acetate molecules emitted by other sympatric Yponomeuta species as to its own saturated tetradecyl acetate pheromone (21). This neuron is also very sensitive to sev- eral other pheromone-like compounds, including (E)-6-tetradecenyl acetate and, most interestingly, with regard to the Roelofs et al report (6), to (E)-and (Z)-12-tetradecenyl acetate.…”