Attraction of a leaf beetle (Oreina cacaliae) to damaged host plants

Early in spring, just after the snow melts, the leaf beetle Oreina caraliae feeds on flowers of Petasites paradoxus. Later in spring they switch to th eir principle host plant Adenostyles alliariae. The attractiveness of short and long-term damaged host plants was studied in a wind tunnel. The spring host P. paradoxus was more attractive to the beetles after it had been dam aged overnight by conspecifics or artificially, but not when the plants wer e damaged half an hour before the wind-tunnel experiments. Contrary to P. p aradoxus the principle host plant, A. alliariac was more attractive shortly after an attack by conspecifics (half an hour before the experiment) compa red to a undamaged plant, but lost its increased attractiveness when damage d overnight. The enhanced attraction of damaged plants was longer lasting i n the spring host P. paradoxus than in the main host A. alliariae. Volatile s emitted by host plants were collected and gas chromatographic analyses of the odors collected showed qualitative and quantitative differences betwee n damaged and undamaged plants. Among the volatiles recorded, green leaf vo latiles and mono- and sesquiterpenes dominated. In overnight damaged P. par adoxus plants with an enhanced attractiveness, limonene was emitted in high er amounts. In freshly damaged A. alliariae leaves, more alpha -humulene an d germacrene D were emitted compared to (E,E)-alpha -farnesene, whereas in the less attractive A. alliariae plants, more (E,E)-alpha -farnesene was em itted compared to alpha -humulene and germacrene D. In the field, the long lasting attraction of flowering P. paradoxus early in the season may facili tate mating in O. cacaliae after a successful overwintering.