Host-plant choice and larval growth in the cinnabar moth: do pyrrolizidinealkaloids play a role?

Witte et al. (1992) described two distinct chemotypes of Senecio jacobaea L . Asteraceae, a chemotype with jacobine as one of the major pyrrolizidine a lkaloids (PAs) and a chemotype with erucifoline as one of the major PAs. We hypothesized that the presence of erucifoline might be the factor responsi ble for the lack of success of the cinnabar moth on Senecio erucifolius L. Asteraceae and the S. jacobaea erucifoline chemotype. We performed a survey of the distribution of the two chemotypes in the Netherlands and compared this with the distribution map of Tyria jacobaeae L. Lepidoptera, Arctiidae . The distribution of the two chemotypes in the Netherlands is poorly corre lated with the distribution of the cinnabar moth. The jacobine chemotype oc curs along the coast and the erucifoline chemotype predominantly inward. An oviposition experiment showed that the cinnabar moth did not discriminat e between the two chemotypes of S. jacobaea and S. erucifolius. Larval perf ormance did not differ between the two chemotypes and species. Although the distribution of S. jacobaea jacobine chemotype is loosely associated with the abundance of the cinnabar moth the oviposition and growth experiments i ndicate that other factors than the presence of erucifoline play a role in this association. The absence of recordings of S. erucifolius as a foodplant for the cinnabar moth might be explained by the phenology of the foodplant. Ovipositing fem ales of the univoltine cinnabar moth prefer flowering plants for ovipositio n. S. erucifolius starts flowering about 1-2 month later than S. jacobaea j ust after the peak density of moths.