Host plant toxins and unpalatability of Neacoryphus bicrucis (Hemiptera: Lygaeidae)

Abstract. 1. Host plant choice of the seed bug, Neacoryphus bicrucis Say (Hemiritera, Lygaeidae), was evaluated in four different Georgia habitats. N. bicrucis utilized only species of Senecio as host plants at a granite outcrop and at old fields on the coastal plain, in the piedmont, and in the Blue Ridge Mountains.
2. In laboratory tests N. bicrucis is distasteful to the green anole lizard, Anolis carolinensis Voight. Only six of ninety field-collected bugs were eaten in palatability trials while eighty-four of the remaining ninety attacked bugs were rejected by lizards without apparent harm. However, the bugs were palatable to Fowler's toads, Bufo woodhousei fowleri Hinckley, which ate all thirty-six bugs offered to them.
3. N. bicrucis selectively sequesters pyrrolizidine alkaloids from Senecio spp. These may cause the insects' distastefulness to green anoles. In palatability trials, lizards ate all twenty insects reared on sunflower seeds, Helianthus annus, but rejected all twenty reared on Senecio smallii.     

Semiochemistry of aposematic seed bugs

(E)-2,7-Octadienyl acetate and (E)-2-octenyl acetate (1:10 by volume) were identified as a pheromone attractive to both sexes of the lygaeid bug, Tropidothorax cruciger. In a parallel investigation of Neacoryphus bicrucis (Lygaeidae), (E,E)-2,4-hexadienyl acetate and phenethyl acetate (≈9:1) were identified from males, and found attractive to both sexes of adults in the field plus a tachinid fly parasitoid of the bugs. In N. bicrucis, the pheromone was clearly shown to come from the tubular accessory glands of the metathoracic scent gland; this evidence, plus earlier literature reports for other species, indicate that male lygaeids are the pheromone emitters. In another lygaeid, Oncopeltus fasciatus, 2-isobutyl-3-methoxypyrazine was identified in the cardiac glycoside-laden fluid sequestered from milkweed hosts and expelled by these bugs when they are attacked. Alkyl methoxypyrazines are warning odorants associated with poisonous insect secretions, and their presence in O. fasciatus indicates that the plant-derived chemical defense of lygaeines is more elaborate than previously appreciated.