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 2 species of Encyrtidae. The first, Epidinocarsis lopezi [Apoanagyrus lopezi], is a monophagous parasitoid of the cassava pest Phenacoccus manihoti, itself feeding exclusively on cassava. The second, Leptomastix dactylopii, is a monophagous parasitoid of the citrus pest Planococcus citri, but the 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 carried out using the following: healthy host-plant alone; host-plant infested with unparasitized mealybugs; unparasitized mealybugs only; host-plant infested with parasitized mealybugs; and parasitized mealybugs only. Only A. 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 the host-plant, induced an undirected activity. The attraction of A. lopezi to the odour of the host-plant alone could be linked to the monophagous diet of its host, whereas the attraction of the 2 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.