We tested the protective function of larval wax covers in the two ladybird beetle species, Scymnus nigrinus and S. interruptus, against cannibalism, predation and ant aggression, and its importance for the distribution of both species in the field. Cannibalism was generally very low and not influenced by the presence or absence of the wax cover, or by larval size. Fourth-instar larvae of three ladybird species, Adalia bipuncata, Exochomus quadripustulatus and Harmonia quadripunctata, consumed Scymnus larvae-which are much smaller-regularly, independent of the presence or absence of waxes. By contrast, first-instar larvae of the three species had generally little success when attacking Scymnus spp. larvae. Wax-covered S. interruptus larvae survived significantly more attacks by the predacious carabid beetle Platynus dorsalis than larvae without wax cover. Wax-covered S. interruptus larvae and S. nigrinus larvae survived attacks by workers of the ant species, Lasius niger and Formica polyctena, respectively, significantly more often than larvae without wax covers. We show that, in the field, Scymnus larvae have higher densites in ant-attended resources than in unattended ones and conclude that both Scymnus species benefit from the ability to feed in ant-attended aphid colonies by a reduced predation risk.
Keywords: Ant predation; Cannibalism; Coccinellidae; Field distribution; Protective waxes.