Research paperHost range patterning of parasitoid wasps Aphidiinae (Hymenoptera: Braconidae)
Introduction
Insect parasitoids, their phytophagous hosts and their host plants compose a major proportion of the world's biodiversity (Hawkins, 1994). Aphidiinae are solitary koinobionts, endoparasitoids that lay a single egg into the aphid body (Aphididae, Hemiptera) (Völkl and Mackauer, 2000). They represent one of the most important and best investigated groups because of their significant role in biocontrol as aphid natural enemies. Previous studies of Aphidiinae have included their morphology, taxonomy and phylogeny (Smith et al., 1999) as well as behaviour and ecology (Völkl and Mackauer, 2000).
A large number of patterns in host-parasitoid interactions can be designed taking into account many different parameters (Hawkins, 1994). Host specificity is defined as a continuum from extreme specialists with a host-range restricted to a single host species to those which have a broad host-range, considered as generalists. In addition, the term host-range, applied to an insect, represents the sum of plant or animal species which are its hosts (van Klinken, 1999). Information regarding the trophic associations between parasitoids and their hosts is very important, especially for the biological control programs (e.g., Starý, 1970, Hågvar and Hofsvang, 1991, Trdan, 2005). Aphidiinae show very different range in host specificity, even among the species belonging to the same genus. In response to selective pressures, some populations of the same parasitoid species may follow different evolutionary trajectories (Hufbauer and Roderick, 2005). Zepeda-Paulo et al. (2013) investigated the existence of local host adaptation in Aphidius ervi (Haliday, 1834) by examining relevant traits related to infectivity and virulence on different hosts (native and alochtonous aphid species) showing significant variability of parasitoid fitness.
A large number of patterns in host-parasitoid interactions aiming to explain host specificity have been published, in the first place it is the host range of parasitoids. In addition, Starý (1981a) split aphidiines into five host specificity groups using its host range: (1) a single host species, (2) two or more species of the same aphid genus, (3) species of two or more genera of the same aphid subfamily, (4) species of two or more genera of two or more subfamilies of the same aphid family, (5) species of several genera of two or more aphid families. This classification mostly relies on aphid phylogeny, taking into account phylogenetic relations among aphid hosts (related genera and families, nowadays aphid subfamilies). Based on this classification, various strategies and/or aphid’s biological control programs have been proposed by Starý and Rejmánek (1981), and later by Boivin et al. (2012). Until today, many authors worldwide (e.g., Starý, 1979, Starý, 2006, Shi and Chen, 2001, Kavallieratos et al., 2004, Žikić et al., 2012, Rakhshani et al., 2012, Barahoei et al., 2014) have invested much effort into investigating pattern tritrophic chains. Thus, new connections between plants, aphids, and parasitoids have been revealed over trophic associations, solving the problem of previous synonymization.
After almost 35 years since previous publications concerning aphidiines host specificity (Starý, 1981a), there is a need to revise this topic, having in mind that many new taxa of Aphidiinae have been described. Also, many species have been introduced in new niches intentionally, through various biological control programs, or unintentionally, by importing plants from one geographical region to another. Development of new methods in ecology allows the consideration and integration of a very large number of parameters which are possible to estimate nowadays.
Having all this in mind, the main goal of this study was to test host specificity over the host range of all valid species of Aphidiinae in the world fauna, including the species of the southern hemisphere. The aim was to define the classes and thresholds of host specificity for Aphidiinae wasps, using the specific spectre of host species, genera and subfamilies which they prefer. To achieve this, the following tasks were set: (1) to examine the host range for each parasitoid species over quantification of used data, not taking into account the phylogenetic relations among aphid hosts, (2) to pattern parasitoid host specificity which rely on host range, (3) to present a vast dataset in the most effective way through visible and comparable output graphs, (4) to test how diversity of plant species as members of tritrophic associations, as well as the Aphidiinae distributional gradient affect the host range among parasitoids and (5) to examine host specificity patterns along the phylogenetic tree.
Section snippets
Material and methods
We sampled data of the world fauna of Aphidiinae subfamily counting 505 species belonging to 38 genera. Furthermore, there are approximately 5000 described species of aphids distributed in 250 genera and 20 subfamilies (Remaudière and Remaudiere, 1997), with the major percentage described in the temperate zones (Blackman and Eastop, 2006). The diversity of plants as first trophic members in this analysis was presented with more than 6500 species (Table S1). For this research we sampled as much
Results
The SOM analysis of the host specificity in Aphidiinae species produced five groups marked as: A, B, C, D and E (Fig. 1). The Kruskal–Wallis and Mann–Whitney tests revealed the classification criteria which defined the trophic groups that were previously obtained by SOM (Table 1). Component planes showed how classification criteria (aphid host species, genus, and subfamily) vary along the defined groups (Fig. 2). Group A consists of almost one half of the Aphidiinae (225 taxa; Table 2),
Discussion
The key result of the present study is an overall host specificity analysis of the world aphidiines excluding any previous reference to the taxonomic and phylogenetic relations among parasitoids, as well as for the aphid hosts. The entire concept of parasitoid host range is complex, and its measurement is difficult (Shaw, 1994), and selecting the adequate parameters to interpret those associations will always be criticized. However, having in mind that the categorisation of parasitoids from
Acknowledgment
We would like to thank to Dr. Olivera Petrović-Obradović (Faculty of Agronomy, Belgrade, Serbia) for the alignment of aphid subfamilies with the recent classification. Also, we would like to thank to Dr. Petr Starý (Institut of Entomology, České Budějovice, Czech Republic) and Dr. Ana Ivanović (Faculty of Biology, Belgrade, Serbia) for the great help in interpreting the results of this study. Proofreading was done by Dr. Lydia Mitits and Antonis Mylonopoulos. This work is supported by the Grant
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