Behaviour of a specialist parasitoid, Cotesia melitaearum: from individualbehaviour to metapopulation processes

1. Foraging behaviour and movement within and among host patches of the spe cialist parasitoid wasp Cotesia melitaearum (Braconidae) attacking the larv ae of Melitaea cinxia (Nymphalidae) were studied in the field and in the la boratory. 2. In the field, female wasps aggregated in large host groups in the autumn and caused positive spatial density-dependent parasitism in the field. Was ps stayed longer with groups of pre-diapause caterpillars than with post-di apause caterpillars, but attacked them less frequently. 3. In the laboratory, wasps attacked larger larvae more readily than smalle r larvae. Also in the laboratory, wasps exposed to larvae outside their pro tective webs showed differences in the rates at which they attacked larvae fed different diets, implicating host plant-derived chemicals as proximate cues for foraging wasps. 4. Mark-recapture studies indicated that there was a low rate of successful movement of wasps among groups of young larvae within a habitat patch in t he autumn and no successful movement of wasps across non-habitat. In contra st, wasps moved frequently among groups of late-instar caterpillars in the spring. 5. Host caterpillars of different ages responded very differently to wasp a ttacks. Pre-diapause larvae remained in groups and used collective head-jer king behaviour to defend themselves, whereas post-diapause larvae dispersed away from the group immediately after being attacked. 6. Population and metapopulation level dynamics of the host-parasitoid inte raction are discussed in light of these observations of the behaviour of in dividual wasps.