Abstract
Parasitoids searching for polyphagous herbivores can find their hosts in a variety of habitats. Under this scenario, chemical cues from the host habitat (not related to the host) represent poor indicators of host location. Hence, it is unlikely that naïve females show a strong response to host habitat cues, which would become important only if the parasitoids learn to associate such cues to the host presence. This concept does not consider that habitats can vary in profitability or host nutritional quality, which according to the optimal foraging theory and the preference-performance hypothesis (respectively) could shape the way in which parasitoids make use of chemical cues from the host habitat. We assessed innate preference in the fruit fly parasitoid Diachasmimorpha longicaudata among chemical cues from four host habitats (apple, fig, orange and peach) using a Y-tube olfactometer. Contrary to what was predicted, we found a hierarchic pattern of preference. The parasitism rate realized on these fruit species and the weight of the host correlates positively, to some extent, with the preference pattern, whereas preference did not correlate with survival and fecundity of the progeny. As expected for a parasitoid foraging for generalist hosts, habitat preference changed markedly depending on their previous experience and the abundance of hosts. These findings suggest that the pattern of preference for host habitats is attributable to differences in encounter rate and host quality. Host habitat preference seems to be, however, quite plastic and easily modified according to the information obtained during foraging.
Highlights
Host plants are a major source of information for insect parasitoids during host searching [1,2,3], even when they are not infested [4,5,6]
If the nutritional quality of the herbivore host varies among plant species, natural selection should favour female parasitoids that are attracted to plants in which the hosts are nutritionally better [23,24,25,26], a concept known as the preference–performance hypothesis (PPH) [27,28]
We addressed the innate preference of D. longicaudata females among odours from four host habitats and, when a preference pattern was found, we tested both the PPH and the potential benefits in terms of parasitization rate
Summary
Host plants are a major source of information for insect parasitoids during host searching [1,2,3], even when they are not infested [4,5,6]. The type of chemical cues used by parasitoids during host searching has been related by Vet and Dicke [11] to the range of plant species where the host can be found. An innate response towards chemical cues could have evolved from some host-plant systems if the reward in terms of cumulative fitness varies among them [22]. If the nutritional quality of the herbivore host varies among plant species, natural selection should favour female parasitoids that are attracted to plants in which the hosts are nutritionally better [23,24,25,26], a concept known as the preference–performance hypothesis (PPH) [27,28]. PPH has been widely studied in bi-trophic scenarios: host plant-herbivore (see Gripenberg et al [28] and references ) and parasitoid-herbivore host [29,30,31]
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