SEMIOCHEMISTRY OF APOSEMATIC SEED BUGS

(E)-2,7-Octadienyl acetate and (E)-2-octenyl acetate (1:10 by volume) were identified an a pheromone attractive to both sexes of the lygaeid bug, Tropidothorax cruciger. In a parallel investigation of Neacoryph us bicrucis (Lygaeidae), (E, E)-2,4-hexadienyl acetate and phenethyl a cetate (approximate to 9:1) were identified from males, and found attr active to both sexes of adults in the field plus a tachinid fly parasi toid of the bugs. In N. bicrucis, the pheromone was clearly shown to c ome from the tubular accessory glands of the metathoracic scent gland; this evidence, plus earlier literature reports for other species, ind icate that male lygaeids are the pheromone emitters. In another lygaei d, Oncopeltus fasciatus, 2-isobutyl-3-methoxypyrazine was identified i n the cardiac glycoside;laden fluid sequestered from milkweed hosts an d expelled by these bugs when they are attacked. Alkyl methoxypyrazine s are warning odorants associated with poisonous insect secretions, an d their presence in O. fasciatus indicates that the plant-derived chem ical defense of lygaeines is more elaborate than previously appreciate d.