Biological control is the central stone of Integrated Pest Management (IPM) paradigm and natural enemies are becoming an increasingly desirable prospect. Parasitoids are a widely used group of invertebrate natural enemies as biological control agents and several species are being used to control various aphid pests. In recent years, an increasing emphasis is being given to the conservation and manipulation of naturally-occurring populations of parasitoids in agricultural ecosystems over traditional approaches to biological control. But these approaches must be underpinned by basic knowledge in host preference behaviour and ecology of the parasitoid species being manipulated. Three aspects of host preference behaviour, namely host recognition, host acceptance and host suitability have been discussed in this paper. Parasitoids’ host selection strategy is based on using long-range and short-range cues. Parasitoids respond to both semiochemical and physical stimuli to locate and recognise their hosts. These responses are either due to aphid sex pheromones acting as kairomones, or due to aphid-induced plant volatiles, acting as synomones. Various interactions like genetic, learning and conditioning factors, which play an important role in host selection behaviour of foraging parasitoids, have been discussed. The learning ability provides the parasitoid with behavioural plasticity to adapt its responses to suit prevailing foraging opportunities and the maintenance of genetic variability within natural populations of parasitoids may promote long-term population stability and help conserving genetic diversity by ensuring flexibility in host selection.
Key words: Aphid parasitoids, host preference, host selection, host recognition, host acceptance, host suitability, conservation of aphid parasitoids, manipulation of parasitoid behaviour, habitat.
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