Host acceptance behaviour of the small ermine moth Yponomeuta cagnagellus:larvae and adults use different stimuli

The sugar alcohol dulcitol is a strong feeding stimulant for larvae of the small ermine moth Yponomeuta cagnagellus. In this paper we tested the hypot hesis that dulcitol also acts as an oviposition stimulant for this species. We found that the sugar-alcohol dulcitol was present on the surface of the host Euonymus europaeus. We also showed that (as yet unidentified compound s) can be systemically transferred (i.e. by uptake and transport via the va scular system) from E. europaeus, to the non-host Crataegus monogyna and st imulate oviposition. However, no evidence was found that this stimulatory a ctivity was due to dulcitol. Systemic enrichment of C. monogyna with dulcit ol did not induce oviposition on this plant. Neither was the application of pure dulcitol on artificial twigs effective. In addition it was shown that when dulcitol was removed from host plant extracts, oviposition stimulator y activity was retained in the fraction without dulcitol. Synergism between dulcitol and other stimulants could not be demonstrated, however, high con centrations of dulcitol in combination with the main stimulant(s) showed a trend towards enhanced oviposition. It is concluded that the sugar alcohol dulcitol can only play a limited role in adult host acceptance behaviour. T he hypothesis that a host shift in the genus Yponameuta from Celastraceae t o Rosaceae might have been facilitated by the presence of small amounts of dulcitol in Rosaceae therefore needs to be restricted to larval feeding beh aviour.