Host location and discrimination mediated through olfactory stimuli in two species of Encyrtidae

The role of olfactory stimuli in host detection and evaluation was studied in two encyrtid Hymenoptera. The first, Epidinocarsis lopezi De Santis, is a monophagous parasitoid of the cassava mealybug Phenacoccus manihoti Matile‐Ferrero, itself feeding exclusively on cassava, Manihot esculenta Crantz. The second, Leptomastix dactylopii Howard, is a monophagous parasitoid of the Citrus mealybug, Planococcus citri Risso, but this latter is highly polyphagous. The behaviour of females of both parasitoids (attraction and locomotion) was compared in a tubular olfactometer for the odours of their respective hosts on cassava and poinsettia. Tests were made using: 1) healthy host‐plant alone; 2) host‐plant infested with unparasitized mealybugs; 3) unparasitized mealybugs only; 4) host‐plant infested with parasitized mealybugs and 5) parasitized mealybugs only. Only E. lopezi was attracted by the odour of the host‐plant alone, but both species were attracted by the odour of an infested host‐plant and that of unparasitized mealybugs. The odour of parasitized mealybugs, alone or on host‐plant, induced an undirected activity. The attraction of E. lopezi to the odour of the host‐plant alone could be linked to the monophagous diet of its host, whereas the attraction of the two species of parasitoids to the odours of infested host‐plants and unparasitized mealybugs could be due to the fact that both parasitoids are specialists. The behavioural response of both species to the odour of parasitized mealybugs revealed a new aspect in host discrimination: the identification of parasitized hosts could be partly mediated through olfactory stimuli, and not only through gustatory stimuli.