OVIPOSITION STIMULANTS FOR THE BLACK SWALLOWTAIL BUTTERFLY - IDENTIFICATION OF ELECTROPHYSIOLOGICALLY ACTIVE COMPOUNDS IN CARROT VOLATILES

Headspace volatiles were collected from undamaged foliage of carrot, D aucus carota, a host-plant species of the black swallowtail butterfly, Papilio polyxenes. The volatiles were fractionated over silica on an open column, and the fractions were tested in behavioral assays with P . polyxenes females in laboratory experiments. The polar fractions, as well as the total mixture of volatiles, increased the landing frequen cy and the number of eggs laid on model plants with leaves bearing con tact-oviposition stimulants. The nonpolar fraction, containing the mos t abundant compounds in carrot odor, was not stimulatory. Gas chromato graphic (GC) separation of the fractions was coupled with electroanten nogram (EAG) recordings to identify the compounds perceived by P. poly xenes females. The EAG activity corresponded to the behavioral activit y of the fractions. None of the nonpolar compounds, identified as vari ous monoterpenes, evoked a major EAG response, but several constituent s of the polar fractions elicited high EAG responses. Sabinene hydrate (both stereoisomers), 4-terpineol, bornyl acetate, and (Z)-3-hexenyl acetate were identified by GC-MS as active compounds.