Abstract
Early experience of olfactory stimuli associated with their host–plant complex (HPC) is an important driver of parasitoid foraging choices, notably leading to host fidelity. Mechanisms involved, such as peripheral or central modulation, and the impact of a complex olfactory environment are unknown. Using olfactometer assays, we compared HPC preference of Aphidius ervi Haliday (Hymenoptera:Braconidae) females originating from two different HPCs, either with the other HPC in close vicinity (complex environment) or without (simple environment). We also investigated antennal responses to volatiles differentially emitted by the two respective HPCs. In a simple environment, HPC of origin had an influence on olfactory choice, but the preferences observed were asymmetric according to parasitoid origin. Electroantennographic recordings revealed significant sensitivity differences for some of the tested individual volatiles, which are emitted differentially by the two HPCs. Besides, presence of an alternative HPC during early stages modified subsequent parasitoid preferences. We discuss how increased olfactory complexity could influence parasitoid host foraging and biological control in diversified cropping systems.
Highlights
In order to find suitable hosts, female parasitoids of phytophagous insects use a wide array of sensory cues, generally emitted directly by the hosts themselves or by the plants on which they feed [1,2]
Females originating from the A. pisum/faba bean HPC (ApF) host–plant complex (HPC), without host switching, spent significantly more time in the olfactometer branches with odors from their HPC of origin than in the branches with the alternative HPC odors (SaB) (Figure 2A, Table 1)
A preference for the volatiles emitted by the A. pisum/faba bean HPC was shown in populations of A. ervi collected on this complex and reared on it for many generations, and for populations of A. ervi collected on this complex and reared on it for many generations, and for populations collected and reared on the alternative HPC but switched on A. pisum/faba bean for one generation collected and reared on the alternative HPC but switched on A. pisum/faba bean for one generation only
Summary
In order to find suitable hosts, female parasitoids of phytophagous insects use a wide array of sensory cues, generally emitted directly by the hosts themselves or by the plants on which they feed [1,2]. Whereas specialist species generally rely on innate preferences [3], such innate preferences for the most suitable host in generalist species are in many cases modified by experience. Learning of host-related cues during larval development or just after adult emergence in generalist species can lead to host fidelity, i.e., the preference for the host–plant complex on which they developed [6]. This mechanism could help parasitoids to effectively forage for the most abundant species when resource availability varies over generations [7], but may represent a first step towards speciation [8,9]. Antennal odor detection has Insects 2019, 10, 127; doi:10.3390/insects10050127 www.mdpi.com/journal/insects
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