Chemical characterization and species specificity of sex pheromones of plusiinae moths in Israel.

The female sex pheromones of four sympatric Plusiinae species, Autographa gamma, Chrysodeixis chalcites, Cornutiplusia circumflexa, and Trichoplusia ni were investigated in Israel. The research concentrated on the behavioral reproductive isolation regulated by their sex pheromones. The chemical composition of the four sex pheromones was determined by analysis of pheromone gland extracts, and in addition entrained volatiles released from virgin female C. chalcites and T. ni were also analyzed. The pheromones of these latter two species were found to contain several components, among which Z7-12:Ac was the main one. The pheromone glands of A. gamma and C. circumflexa were found to contain relatively small amounts of material and only Z7-12:Ac and Z7-12:OH could be positively identified. These two pheromone components were present in the two species in roughly inverse ratios. Whereas A. gamma utilizes Z7-12:Ac as the main or sole pheromone component, C. circumflexa requires both Z7-12:OH and Z7-1 2:Ac, with the alcohol being predominant. This is the first reported Plusiinae species using Z7-12:OH as the main pheromone component. Behavioral studies in the wind tunnel and field tests indicate that females of each of the four Plusiinae species utilizes a species-specific blend of chemicals, consisting of attractive and antagonistic components, to attract conspecific males. Such a complementary strategy provides improved behavioral reproductive isolation among the sympatric species. For example, Z5-12:Ac, which is a specific component of the T. ni sex pheromone, may be redundant as regards the attraction of T. ni males. However, addition of small amounts of this compound to pheromone blends of A. gamma and C. chalcites resulted in complete inhibition of the males' flight behavior and trap catch; thus contributing significantly to the specificity of the T. ni sex pheromone. The relatively high proportion of Z7-1 2:OH in the sex pheromone of C. circumflexa, essential to the latter, is highly inhibitory to the three other Plusiinae species. The only case of cross-attraction occurred when T. ni males were attracted to a certain extent to A. gamma lures and females.