The feeding stimulatory activity on the white pine weevil, Pissodes strobi Peck, of various types of extracts from Sitka spruce, Picea sitchensis (Bong.) Carr., was tested using a paired agar disc bioassay. Chemicals that induce feeding apparently constitute a complex mixture of non-volatile compounds in the phloem and on the surface of the bark and needles. Volatile chemicals from the bark and foliage, captured in Porapak Q, did not attract walking P. strobi in two olfactometers, nor did they trigger a feeding response when tested on plain agar. However, the monoterpenes α-pinene, β-pinene, and β-myrcene acted as synergists to the nonvolatile chemicals in the bark, while piperitone had a marked feeding deterrent effect. (+)-Camphor and limonene stimulated the feeding at low concentrations but caused feeding inhibition when the concentration rose above a particular threshold.
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Alfaro et al. (1980) studied this question.