Pheromone identification by proxy: identification of aggregation-sex pheromones of North American cerambycid beetles as a strategy to identify pheromones of invasive Asian congeners

Research over the past decade has shown that attractant pheromones used by cerambycid beetles are often highly conserved, with the same compound being used as a pheromone component by multiple related species, even among species on different continents which have been separated for millions of years. We describe how this conservation of structures can be exploited to identify possible pheromone components for Asian target species with a high risk of invading North America. Thus, collection and analysis of volatiles from five North American species, Semanotus amethystinus (LeConte), Semanotus ligneus (F.), Semanotus litigiosus (Casey), Callidium antennatum hesperum Casey, and Callidium pseudotsugae Fisher, showed that males of the two Callidium species sex-specifically produced 3-hydroxyhexan-2-one, a previously known cerambycid pheromone component, along with a novel natural product, 1-(1H-pyrrol-2-yl)-1,2-propanedione (henceforth pyrrole). In contrast, males of the three Semanotus species produced only the pyrrole. In field bioassays, both sexes of C. antennatum hesperum were significantly attracted to the blend of the two compounds, and S. amethystinus were equally attracted to the pyrrole alone, or the blend of the two compounds. Even before completing field bioassays with these species in California, field testing of the two compounds in Japan and China had revealed that several related target species, including the invasive Callidiellum rufipenne (Motschulsky), Callidiellum villosulum (Fairmaire), and Semanotus bifasciatus (Motschulsky), were attracted to one or both compounds (data reported elsewhere), providing proof of concept of the pheromone identification by proxy strategy.