Host-age discrimination during host location by Cotesia glomerata, a larval parasitoid of Pieris brassicae.

Some parasitoids are restricted with respect to the host stage that they attack and even to a certain age within a stage. In this paper we investigate whether the parasitoid Cotesia glomerata can discriminate between old and young caterpillar instars of its host, Pieris brassicae, before contacting these hosts, since contacts with older instars are very risky with a chance of being killed, due to the aggressive defensive behaviour of the caterpillars.