Spectral efficiency and microstructure of the compound eyes ofSynanthedon myopaeformis(Lepidoptera: Sesiidae)

The apple clearwing moth,Synanthedon myopaeformis(Borkhausen) (Lepidoptera: Sesiidae), is a day-flying species that feeds on floral nectar of many plants. In British Columbia, Canada, this invasive moth is often observed feeding on visually conspicuous showy milkweed,Asclepias speciosaTorrey (Apocynaceae). We measured the spectral efficiency of the compound eyes ofS. myopaeformisin the context of their capacity to discriminate the measured spectral reflectance from inflorescences ofA. speciosa, and conducted histological examination of these eyes to determine whether they possess apposition type ommatidia, as commonly observed in diurnal butterflies. Light micrographs of the compound eyes inS. myopaeformisrevealed eucone apposition type ommatidia, which is consistent with the diurnal behaviour of the moth. Electroretinograms on compound eyes revealed they were particularly efficient at absorbing ultraviolet (UV) wavelengths in the 335–370 nm range and green wavelengths in the 495–560 nm range. These results support the conclusion that the compound eyes ofS. myopaeformishave the capacity for dichromatic vision based on UV and green photoreceptors. However, spectral reflectance curves obtained from inflorescences and foliage ofA. speciosarevealed no evidence of UV reflectance, making it less likely that colour plays a primary role in the attraction ofS. myopaeformistoA. speciosa.