Chemical ecology of insect parasitoids: essential elements for developing effective biological control programmes

Insect parasitoids can find their hosts in complex environments and reproduce through a series of behavioural steps which are regulated mainly by chemical cues, termed semiochemicals. According to functional criteria, stimuli can be classified into four main categories: (A) cues coming from the habitat, the host microhabitat or the food plant, (B) direct host‐related cues, (C) indirect host‐related cues, and (D) cues coming from the parasitoid itself. In recent years, considerable progress has been made in elucidating the semiochemicals used by parasitoids to locate their hosts. Several studies provided interesting prospective for manipulating foraging behaviour of parasitoids in order to increase their impact on pest populations. However, most of the research has been conducted mainly under laboratory conditions, which differ considerably from field conditions, especially in agro‐ecosystems in which human activities modify the tritrophic interactions between plants, phytophagous insects, and parasitoids. As a consequence, it is often not known how to employ semiochemicals in the field to successfully manipulate parasitoids in order to improve their efficiency in biological control programs and the simple application of semiochemicals could be counter‐productive. In order to provide essential elements for developing effective biological control programmes, we critically review recent research on different strategies to manipulate parasitoid behavior for the conservation or the recruitment of parasitoids within agro‐ecosystems. We show where the complexity of the system should be consideredwhen accompanying the introduction and/or the conservation of natural enemy populations within agro‐ecosystems by exploiting tritrophic interactions and manipulation of parasitoid behavioral responses to chemical cues.