The synthetic aggregation pheromone of the large milkweed bug, Oncopeltus fasciatus (Dallas) (Lygaeinae), also attracted males of the plant bug, Phytocoris difficilis Knight (Miridae). Field-testing partial blends against the six-component blend comprising the Oncopeltus pheromone showed that cross-attraction of P. difficilis males was due to a synergism between (E)-2-octenyl acetate and (E,E)-2,4-hexadienyl acetate. The combination of hexyl, (E)-2-hexenyl and (E)-2-octenyl acetates was as attractive to P. difficilis males as was the milkweed bug pheromone, yet no milkweed bugs were drawn to this blend. GC-electroantennographic detection (EAD) and GC-MS analysis of female P. difficilis MSG’s determined that their secretion contained predominantly hexyl, (E)-2-hexenyl and (E)-2-octenyl acetates (all strongly EAD-active)—the latter two compounds found only in trace amounts from males—plus five minor female-specific compounds, three of which were EAD-active. (E,E)-2,4-Hexadienyl acetate was not detected from P. difficilis females or males. The blend of the three major components, hexyl, (E)-2-hexenyl and (E)-2-octenyl acetates (2: 1.5 :1 by volume), was as attractive as the blend of all six EAD-active compounds identified from females, and this ternary blend constitutes the sex pheromone of P. difficilis. Interestingly, hexyl acetate with (E)-2-octenyl acetate attracted males of another species, P. breviusculus Reuter, but addition of (E)-2-hexenyl acetate and/or (E,E)-2,4-hexadienyl acetate inhibited attraction of P. breviusculus males. Attraction of P. difficilis males occurred mainly during the first half of scotophase. The possible neurophysiological basis for this asymmetrical cross-attraction is discussed.
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