Abstract
1. Parasitoids are known to utilise learning of herbivore‐induced plant volatiles (HIPVs) when foraging for their herbivorous host. In natural situations these hosts share food plants with other, non‐suitable herbivores (non‐hosts). Simultaneous infestation of plants by hosts and non‐hosts has been found to result in induction of HIPVs that differ from host‐infested plants. Each non‐host herbivore may have different effects on HIPVs when sharing the food plant with hosts, and thus parasitoids may learn that plants with a specific non‐host herbivore also contain the host.2. This study investigated the adaptive nature of learning by a foraging parasitoid that had acquired oviposition experience on a plant infested with both hosts and different non‐hosts in the laboratory and in semi‐field experiments.3. In two‐choice preference tests, the parasitoid Cotesia glomerata shifted its preference towards HIPVs of a plant–host–non‐host complex previously associated with an oviposition experience. It could, indeed, learn that the presence of its host is associated with HIPVs induced by simultaneous feeding of its host Pieris brassicae and either the non‐host caterpillar Mamestra brassicae or the non‐host aphid Myzus persicae. However, the learned preference found in the laboratory did not translate into parasitisation preferences for hosts accompanying non‐host caterpillars or aphids in a semi‐field situation.4. This paper discusses the importance of learning in parasitoid foraging, and debates why observed learned preferences for HIPVs in the laboratory may cancel out under some field experimental conditions.
Highlights
The ability to learn to associate certain cues with the presence of a food reward is important for animals to optimise their foraging success (Ishii & Shimada, 2010; Hoedjes et al, 2011; Mery, 2013; Dridi & Lehmann 2016)
The landing preference of C. glomerata parasitoids shifted in the direction of plants infested by hosts plus non-host aphids if, previously, cues from non-host aphids were experienced in the presence of hosts
C. glomerata parasitised hosts on similar numbers of plants infested by hosts plus non-host caterpillars as on plants infested by hosts plus non-host aphids, irrespective of their previous experience
Summary
The ability to learn to associate certain cues with the presence of a food reward is important for animals to optimise their foraging success (Ishii & Shimada, 2010; Hoedjes et al, 2011; Mery, 2013; Dridi & Lehmann 2016). Mixed infestations of plants with host and non-host herbivores affect the HIPVs and herbivore-related cues that parasitoids encounter during foraging for hosts By the induction of different volatile blends and the production of different herbivore-related direct cues, the presence of non-host herbivores with various feeding styles partly determines the olfactive environment of the parasitoid (De Rijk et al, 2013; Aartsma et al, 2017). Learning to associate HIPVs of a specific plant–host–non-host complex with host presence may allow parasitoids to fine-tune their foraging in environments with various non-host herbivore species
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