Abstract
Host range in parasitoids could be described by the preference–performance hypothesis (PPH) where preference is defined as host acceptance and performance is defined as the sum of all species on which parasitoid offspring can complete their life cycle. The PPH predicts that highly suitable hosts will be preferred by ovipositing females. However, generalist parasitoids may not conform to this hypothesis if they attack a large range of hosts of varying suitability. Under laboratory conditions, we tested the PPH relationship of three aphid parasitoids currently considered as generalist species (Aphelinus abdominalis, Aphidius ervi, Diaeretiella rapae). As expected, the three parasitoids species showed low selectivity, i.e., females stung all aphid species encountered (at least in some extent). However, depending on the parasitoid species, only 42%–58% of aphid species enabled producing parasitoid offspring. We did not find a correlation between the extent of preference and the performance of three generalist aphid parasitoids. For A. ervi, host phylogeny is also important as females showed higher attack and developmental rates on hosts closely related to the most suitable one. In addition, traits such as (a) the presence of protective secondary endosymbionts, for example, Hamiltonella defensa detected in Aphis fabae and Metopolophium dirhodum and (b) the sequestration of plant toxins as defense mechanism against parasitism, for example, in Aphis nerii and Brevicoryne brassicae, were likely at play to some extent in narrowing parasitoid host range. The lack of PPH relationship involved a low selectivity leading to a high adaptability, as well as selection pressure; the combination of which enabled the production of offspring in a new host species or a new environment. Testing for PPH relationships in parasitoids may provide useful cues to classify parasitoids in terms of specialization degree.
Highlights
Host specificity, and more broadly diet breath, has been described by the preference–performance hypothesis (PPH) of Jaenike (1978)
The selection of hosts by parasitoids involves the detection of physical and/or chemical cues from the other trophic levels (Mackauer, Michaud, & Völkl, 1996; Vet & Dicke, 1992; Vinson, 1985), and the host specificity of parasitoids may be mainly shaped by infochemicals, i.e., chemicals emitted by host and/or host plant (Afsheen, Wang, Li, Zhu, & Lou, 2008)
The sex ratio was male‐biased in M. dirhodum, M. persicae, and R. padi and female‐biased in M. euphorbiae on tomato (p = 0.036; Table 4)
Summary
More broadly diet breath, has been described by the preference–performance hypothesis (PPH) of Jaenike (1978) It predicts a positive relationship between the choice of adult females (preference) and the degree of successful offspring development (performance). Specialist parasitoids may use more specific cues related to their hosts (Barbosa, 1988; McCormick, Unsicker, & Gershenzon, 2012; Vet & Dicke, 1992) This is the case, for example, for Microplitis croceipes that uses host kairomones from a variety of host‐related sources (e.g., frass, hemolymph, and salivary secretions; Alborn, Lewis, & Tumlinson, 1995; Jones, Lewis, Bowman, Beroza, & Bierl, 1971). The generalist fly parasitoid Aphaereta minuta does not use host‐derived chemical cues to select host larvae and attacks almost all hosts that are present in encountered decaying materials (Vet, 1985)
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