Boletín de la AeE

Parasitoids use stimuli from different odour sources to lócate their hosts. These stimuli are many and varied, and the behaviours that the stimuli elícit in various species of parasitoids are equally varied. In the last 20 years research has been focused on the modalities and nature of the stimuli involved, and the behaviours that these stimuli elicits (reviewed i.e. by Vinson, 1991 and Godfray 1994).

Already at the beginning of the ´80s, Price and coworkers (1980) emphasized that all terrestrial communities are based on at least three interacting trophic levéis: plants, herbivores and natural enemies of herbivores. They argued that ecological research could not progress realistically without consideration of the interactions among all levéis involved.

In this framework an impressive amount of experimental evidence has been provided in the last few years to demónstrate that parasitoids use plant volátiles to lócate their herbivore hosts (for reviews see Dicke et al, 1990b, Vet & Dicke 1992, Turlings et al, 1993b, Dicke 1994). Foraging parasitoids can even discriminate between the volátiles emitted by mechamcally-damaged plants and those of a herbivore-damaged plants. Recently the concept of semiochemically mediated hostlocation in a tritrophic context has been extended to ecosystems based on stored producís such as wheat grain and clothes. For example Lariophagous disUngiiendits, a parasitoid of the granary weevil Siiophihis granarius, can discriminate between the volátiles emitted by infested grains vs. non infested grains (Steidle and Schóller, 1997). Tackács et al (1997) demonstrated that Apanleles carpalus, a braconid parasitoid of Tineid larvae locates the host through chemical emitted by infested beaver or rabbit pelts which are preferred to non-infested pelts.

In contrast with the wealth of knowledge available on the behavioural and semiochemical aspects of the tritrophic interactions, little is known about the biochemical factor(s) eliciting volátiles emission in the host-food (plant or nonliving substrate

In this paper we discuss the function of a digestive enzyme as elicitor that affects the production of parasitoid attractants. The investigation was conducted on a system of Brussels sprouts leaves (Brassica olerácea var. gemmiferá), caterpillars of the large cabbage white butterfly, Pieris brassicae, and the parasitoid Cotesia glomemia. Furtbermore we present data suggesting that the enzyme is a widely distributed and general elicitor of these type of plant responses, exploited by insect camivores.