DISTRIBUTION OF AUTOGENOUS AND HOST-DERIVED CHEMICAL DEFENSES IN OREINA LEAF BEETLES (COLEOPTERA, CHRYSOMELIDAE)

The pronotal and elytral defensive secretions of 10 Oreina species wer e analyzed. Species feeding on Apiaceae, i,e., O. frigida and 0. virid is, or on Cardueae (Asteraceae), i.e., 0. bidentata, 0. coerulea, and 0. virgulata, produce species-specific complex mixtures of autogenous cardenolides. 0. melanocephala, which feeds on Doronicum clusii (Senec ioneae, Asteraceae), devoid of pyrrolizidine alkaloids (PAs) in its le aves, secretes, at best, traces of cardenolides. Sequestration of host -plant PAs was observed in all the other species when feeding on Senec ioneae containing these alkaloids in their leaves. 0. cacaliae is the only species that secretes host-derived PA N-oxides and no autogenous cardenolides. Differences were observed in the secretions of specimens collected in various localities, because of local differences in the vegetation. The other species, such as 0. elongata, 0. intricata, and 0. speciosissima, have a mixed defensive strategy and are able both to synthesize de novo cardenolides and to sequester plant PA N-oxides. T his allows a great flexibility in defense, especially in 0. elongata a nd 0. speciosissima, which feed on both PA and non-PA plants. Populati ons of these species were found exclusively producing cardenolides, or exclusively sequestering PA N-oxides, or still doing both, depending on the local availability of food-plants. Differences were observed be tween species in their ability to sequester different plant PA N-oxide s and to transform them. Therefore sympatric species demonstrate diffe rences in the composition of their host-derived secretions, also resul ting from differences in host-plant preference. Finally, within-popula tion individual differences were observed because of local plant heter ogeneity in PAs. To some extent these intrapopulation variations in ch emical defense are tempered by mixing diet and by the long-term storag e of PA N-oxides in the insect body that are used to refill the defens ive glands.