Carbon stable isotopes:: a tool for studying the mating, oviposition, and spatial distribution of races of European corn borer, Ostrinia nubilalis, among host plants in the field

The European corn borer, Ostrinia nubilalis (Hubner, 1796) (Lepidoptera: Crambidae), is a polyphagous corn pest species that includes two host races: one feeding on corn (Zea mays L.) and one feeding on mugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.). Being able to determine the type of host plant on which field-caught moths fed as larvae would allow for the quantification of mating rates within and between races, as well as the quantification of the spatial distribution and oviposition of both races in the field. We found that stable carbon isotopes (delta(13)C) are a reliable indicator of host-plant photosynthetic type (C3 or C4) regardless of adult food and intensity of metabolism; so even when food or metabolism had a significant effect on wing delta(13)C values, the magnitude of this effect was too small to obscure the signal characterizing host-plant type. Egg and spermatophore delta(13)C values similarly reflect female and male host-plant type, respectively, regardless of adult feeding. We found 224 host-plant species of O. nubilalis in the literature, including 19 species with C4-type photosynthesis. However, in temperate areas, corn is probably the only significant C4 source of adult moths. Accordingly, wing delta(13)C values were more variable in field-caught moths showing a typical C3-type delta(13)C value than in those showing a typical C4-type delta(13)C value.