Visual and olfactory cues used by the apple clearwing moth, Synanthedon myopaeformis (Lepidoptera: Sesiidae), to locate inflorescences of showy milkweed

The apple clearwing moth, Synanthedon myopaeformis Borkhausen (Lepidoptera: Sesiidae), is a recently introduced pest of apples in Canada. In British Columbia, adult moths are attracted to, and feed upon, visually conspicuous and fragrant inflorescences of showy milkweed, Asclepias speciosa (Torrey). I analyzed visual and olfactory cues that might mediate this behaviour. Histological studies of S. myopaeformis eyes revealed apposition ommatidia. In electroretinograms, S. myopaeformis eyes were sensitive to ultraviolet (UV) and green wavelengths, indicating their potential for dichromatic vision. However, inflorescences of A. speciosa do not reflect UV light, and field experiments revealed that S. myopaeformis relies mostly on semiochemicals to locate the inflorescences. Floral semiochemicals were analyzed by coupled gas chromatographic-electroantennographic detection (GC-EAD), GC-mass spectrometry and proboscis extension reflex bioassays. Among the > 10 candidate floral semiochemicals field-tested, phenylacetaldehyde was the most attractive semiochemical for S. myopaeformis. Phenylacetaldehyde shows promise as a lure to monitor or mass-trap S. myopaeformis.