Ontogeny of Defensive Chemistry in Longitarsus Flea Beetles (Coleoptera, Chrysomelidae): More Protection for the Vulnerable Stages?

Several species of the flea beetles genus Longitarsus sequester pyrrolizidine alkaloids (PAs) from their host plants. Previous data demonstrated that PAs may be transferred from root-feeding larvae into the adult beetles. Here we compared the patterns and concentrations found in larvae and pupae of L. anchusae and L. echii with those of the roots of their respective hosts, Symphytum officinale and Echium vulgare (Boraginaceae). PA patterns and concentrations in the roots were complex and variable, whereas those in the larvae and pupae were simpler and more constant. In L. anchusae, intermedine and lycopsamine were the dominant PAs even if they could not be detected in the roots. In L. echii simpler, hydrolized PAs prevailed. Overall, the concentrations of total PAs of larvae and pupae were significantly higher than those of the roots the larvae had been feeding on. Larvae and pupae of both species also had considerably higher PA concentrations than determined previously for field collected beetles. Possibly the rather immobile juvenile stages enjoy a better protection by higher PA concentrations. On the other hand, we could not detect PAs in eggs of either species, indicating that transmission of appreciable amounts of PAs from mother to offspring does not occur.