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Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers

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A special issue of Insects (ISSN 2075-4450).

Deadline for manuscript submissions: closed (30 September 2019) | Viewed by 49169

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Special Issue Editors

Prof. Hugh Loxdale

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Guest Editor

School of Biosciences, Cardiff University, Cardiff, UK
Interests: dispersal ranges of different aphid species; clonal fidelity; generalism vs. specialism; rapid insect evolution; local population genetics of geometrid moths; effects of chromosome telomere lengths on aphid clones; acto-myosin crossbridge cycle of insect flight muscle; exploration of effects of parasites on the behaviour of their insect hosts

Prof. Dr. Astrid T. Groot

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Guest Editor

Faculty of Science, Mathematics and Computer Science Institute for Biodiversity and Ecosystem Dynamics, Amsterdam, The Nederlands
Interests: evolutionary chemical ecology; sexual selection; sex pheromones; population genetics; speciation
Special Issues, Collections and Topics in MDPI journals

Dr. David G. Biron

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Guest Editor

Laboratory Microorganisms: Genome and Environment Build, CNRS National Center for Scientific Research, Paris, France
Interests: parasitism; microorganism; molecular cross-talk; trophic relations; biodiversity dynamics

Special Issue Information

Dear Colleagues,

Natural insect populations are always likely to diverge ecologically under the influences of selection, competition for scarce resources (both intra- and interspecific, including intra- and interclonal in predominantly asexual insects), and genetic drift. This may arise by allopatric, parapatric, or sympatric means. In the case of the last, even though individuals are contiguous within a population, divergence can arise by chromosomal means—for example, complementary and non-complementary regions of the genome where genetic exchange can or cannot occur; fusions and fissions, especially translocations; rearrangements such as inversion polymorphisms brought about by transposon-induced “hot-spots”; mutation of sex determining genes causing asexual populations, as in aphids; possibly mutualistic symbionts leading to unique specialised host insect populations; sexual selection; and polyploidy—to name only the principal mechanisms. There are undoubtedly others, some as-yet unknown. All such mechanisms are liable to produce mutant individuals that can no longer interbreed with the natal population, with divergence perhaps reinforced by chemical means, such as kairomones, pheromones, and cuticular hydrocarbons (CHCs), immune responses, and in some species (e.g., cicadas), auditory mechanisms related directly to behaviour. In the present collection of overview articles, various international experts in the field of molecular ecology and genetics explore how insects have diverged and continue to do so at the molecular-genetic level, sometimes rapidly, to become new ecological entities and thereby new players in the great ongoing panoply of evolution on Earth.

Prof. Hugh Loxdale
Prof. Dr. Astrid Groot
Dr. David G. Biron
Guest Editors

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Published Papers (13 papers)

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18 pages, 2575 KiB

Open AccessArticle

“Generalist” Aphid Parasitoids Behave as Specialists at the Agroecosystem Scale

by Stéphane A.P. Derocles, Yoann Navasse, Christelle Buchard, Manuel Plantegenest and Anne Le Ralec

Insects 2020, 11(1), 6; https://doi.org/10.3390/insects11010006 - 19 Dec 2019

Cited by 11 | Viewed by 3607

Abstract

The degree of trophic specialization of interacting organisms impacts on the structure of ecological networks and has consequences for the regulation of crop pests. However, it remains difficult to assess in the case of parasitoids. Host ranges are often established by listing host records from various years and geographic areas in the literature. Here, we compared the actual hosts exploited at a local farm-scale by aphid parasitoids (Hymenoptera: Aphidiinae), to the available species listed as hosts for each parasitoid species. We sampled aphids and their parasitoids in cultivated and uncultivated areas in an experimental farm from April to November 2014 and thereafter used DNA-based data to determine whether a differentiation in sequences existed. Twenty-nine parasitoid species were found on 47 potential aphid hosts. Our results showed that the great majority of the parasitoid tested used fewer host species than expected according to data published in the literature and parasitized a limited number of hosts even when other potential hosts were available in the environment. Moreover, individuals of the most generalist species differed in their DNA sequences, according to the aphid species and/or the host plant species. At a local scale, only obligate or facultative specialist aphid parasitoids were detected. Local specialization has to be considered when implementing the use of such parasitoids in pest regulation within agroecosystems. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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14 pages, 2258 KiB

Open AccessArticle

Life on the Edge: Ecological Genetics of a High Arctic Insect Species and Its Circumpolar Counterpart

by Jean-Christophe Simon, Frédérique Mahéo, Lucie Mieuzet, Christelle Buchard, Jean-Pierre Gauthier, Damien Maurice, Joël Bonhomme, Yannick Outreman and Maurice Hullé

Insects 2019, 10(12), 427; https://doi.org/10.3390/insects10120427 - 26 Nov 2019

Cited by 4 | Viewed by 2544

Abstract

Arctic ecosystems are subjected to strong environmental constraints that prevent both the colonization and development of many organisms. In Svalbard, few aphid species have established permanent populations. These high arctic aphid species have developed peculiar life-history traits such as shortened life cycles and reduced dispersal capacities. Here, we present data on the distribution and population genetics of Acyrthosiphon svalbardicum in Spitsbergen, the main island of the Svalbard archipelago, and compared its genetic structure with that of its close relative Acyrthosiphon brevicorne, sampled in the top of Scandinavian mainland. We found that A. svalbardicum is common but heterogeneously distributed along the west coast of Spitsbergen. We recorded this species up to 79°12’, which constitutes the northernmost location for any aphid. Genetic structure examined using microsatellite markers showed more pronounced spatial differentiation in A. svalbardicum than in A. brevicorne populations, presumably due to reduced dispersal capacities in the former species. Although populations of A. brevicorne and A. svalbardicum were well-delineated at nuclear loci, they shared similar cytoplasmic DNA haplotypes as revealed by sequence analysis of two DNA barcodes. These results raise questions about whether these two taxa are different species, and the colonization sources and history of the Svalbard archipelago by A. svalbardicum. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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14 pages, 1301 KiB

Open AccessArticle

Unraveling the Genetic Structure of the Coconut Scale Insect Pest (Aspidiotus rigidus Reyne) Outbreak Populations in the Philippines

by Joeselle M. Serrana, Naoto Ishitani, Thaddeus M. Carvajal, Billy Joel M. Almarinez, Alberto T. Barrion, Divina M. Amalin and Kozo Watanabe

Insects 2019, 10(11), 374; https://doi.org/10.3390/insects10110374 - 26 Oct 2019

Cited by 9 | Viewed by 4558

Abstract

Despite the fact that massive outbreaks of the coconut scale insect pest, Aspidiotus rigidus Reyne (Hemiptera: Diaspididae) are inflicting significant economic losses to the Philippines’ coconut industry, little is known about the population and dispersal history of this invasive pest in the country. Here, we examined the genetic diversity, structure and demographic history of A. rigidus sampled from localities with reported outbreaks from 2014 to 2017. We analyzed the genetic structure of the outbreak populations using mitochondrial COI and nuclear EF-1α markers. Both markers and all methods of population genetic structure analyses indicate clear differentiation among the A. rigidus populations separating the north from the southern regions of the Philippines. Very low or no genetic differentiation was observed within and amongst the populations per geographic region indicating two unrelated outbreak events of the pest originating from two genetically uniform populations isolated in each respective region. Historical data supports the resurgence of an established A. rigidus population in the south which could have been driven by sudden climatic changes or human-induced habitat imbalance. Our study provides valuable information on the genetic differentiation of the two A. rigidus groups that would be useful for developing and implementing biological control strategies against this pest in the Philippines. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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12 pages, 3534 KiB

Open AccessArticle

Comparative Analysis of Intra- and Inter-Specific Genomic Variability in the Peach Potato Aphid, Myzus persicae

by Mauro Mandrioli, Deborah Salvatore, Agnese Ferrari, Niccolò Patelli and Gian Carlo Manicardi

Insects 2019, 10(10), 368; https://doi.org/10.3390/insects10100368 - 22 Oct 2019

Cited by 4 | Viewed by 3618

Abstract

The availability of genomic data in the last decade relating to different aphid species has allowed the analysis of the genomic variability occurring among such species, whereas intra-specific variability has hitherto very largely been neglected. In order to analyse the intra-genomic variability in the peach potato aphid, Myzus persicae, comparative analyses were performed revealing several clone-specific gene duplications, together with numerous deletions/rearrangements. Our comparative approach also allowed us to evaluate the synteny existing between the two M. persicae clones tested and between the peach potato aphid and the pea aphid, Acyrthosiphon pisum. Even if part of the observed rearrangements are related to a low quality of some assembled contigs and/or to the high number of contigs present in these aphid genomes, our evidence reveals that aphid clones are genetically more different than expected. These results suggest that the choice of performing genomes sequencing combining different biotypes/populations, as revealed in the case of the soybean aphid, Aphis glycines, is unlikely to be very informative in aphids. Interestingly, it is possible that the holocentric nature of aphid chromosomes favours genome rearrangements that can be successively inherited transgenerationally via the aphid’s apomictic (parthenogenetic) mode of reproduction. Lastly, we evaluated the structure of the cluster of genes coding for the five histones (H1, H2A, H2B, H3 and H4) in order to better understand the quality of the two M. persicae genomes and thereby to improve our knowledge of this functionally important gene family. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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14 pages, 1308 KiB

Open AccessArticle

Expansion of Imaginal Disc Growth Factor Gene Family in Diptera Reflects the Evolution of Novel Functions

by Martina Zurovcova, Vladimir Benes, Michal Zurovec and Lucie Kucerova

Insects 2019, 10(10), 365; https://doi.org/10.3390/insects10100365 - 20 Oct 2019

Cited by 8 | Viewed by 3116

Abstract

Imaginal disc growth factors (IDGFs) are a small protein family found in insects. They are related to chitinases and implicated in multiple functions, including cell growth stimulation, antimicrobial activity, insect hemolymph clotting, and maintenance of the extracellular matrix. A number of new IDGFs have been found in several insect species and their detailed phylogenetic analysis provides a good basis for further functional studies. To achieve this goal, we sequenced Idgf cDNAs from several lepidopteran and trichopteran species and supplemented our data with sequences retrieved from public databases. A comparison of Idgf genes in different species showed that Diptera typically contain several Idgf paralogs with a simple exon-intron structure (2–3 exons), whereas lepidopteran Idgfs appear as a single copy per genome and contain a higher number of exons (around 9). Our results show that, while lepidopteran Idgfs, having single orthologs, are characterized by low divergence and stronger purifying selection over most of the molecule, the duplicated Idgf genes in Diptera, Idgf1 and Idgf4, exhibit signs of positive selection. This characterization of IDGF evolution provides, to our knowledge, the first information on the changes that formed these important molecules. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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21 pages, 1930 KiB

Open AccessArticle

Spatial and Temporal Genetic Diversity of the Peach Potato Aphid Myzus persicae (Sulzer) in Tunisia

by Amen Hlaoui, Sonia Boukhris-Bouhachem, Daniela A. Sepúlveda, Margarita C.G. Correa, Lucía M. Briones, Rebha Souissi and Christian C. Figueroa

Insects 2019, 10(10), 330; https://doi.org/10.3390/insects10100330 - 1 Oct 2019

Cited by 7 | Viewed by 3076

Abstract

The peach potato aphid, Myzus persicae (Sulzer), is a worldwide pest of many crops, and the most important aphid pest of peach and potato crops in Tunisia, mainly due to virus transmission, for which insecticides are frequently applied. We studied the genetic structure of M. persicae populations in Tunisia, in order to further our understanding of the biotic and abiotic factors shaping populations and to predict their evolutionary responses to the present management practices. We monitored peach orchards and seed potato crops in different seasons and regions from 2011–2013 and in 2016 (19 populations), assessing the genetic diversity of M. persicae at six microsatellite loci. Temporal and spatial changes in the frequency and distribution of 397 genotypes in 548 sampled aphids were studied. Only 37 genotypes were found more than once (clonal amplification), as most genotypes were found only once (91.60% in peach; 88.73% in potato crops). A similarly high genetic diversity was observed in aphids sampled from peach (G/N = 0.76; Ho = 0.617) and potato (G/N = 0.70; Ho = 0.641). Only a weak genetic differentiation among populations was found, mainly between geographic locations. Clustering analysis revealed genotypes to be grouped mainly according to host plant. The availability of the primary host, high proportion of unique genotypes, high genetic diversity and lack of structuring suggest that the aphid reproduces mainly through cyclical parthenogenesis in Tunisia. On the other hand, we provide a farm-scale study that shows how easily M. persicae can colonize different areas and hosts, which may have important implications in relation to plant virus vectoring. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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13 pages, 968 KiB

Open AccessArticle

Variation in Performance and Resistance to Parasitism of Plutella xylostella Populations

by Rieta Gols, Gaylord A. Desurmont and Jeffrey A. Harvey

Insects 2019, 10(9), 293; https://doi.org/10.3390/insects10090293 - 11 Sep 2019

Cited by 2 | Viewed by 2566

Abstract

Two major ecological factors determine the fitness of an insect herbivore: the ability to overcome plant resistance strategies (bottom-up effects) and the ability to avoid or resist attack by natural enemies such as predators and parasitoids (top-down effects). In response to differences in selection pressure, variation may exist in host-plant adaptation and immunity against parasitism among populations of an insect herbivore. We investigated the variation in larval performance of six different Plutella xylostella populations originating from four continents when feeding on a native Dutch plant species, Brassica rapa. One of the used populations has successfully switched its host plant, and is now adapted to pea. In addition, we determined the resistance to attack by the endoparasitoid Diadegma semiclausum originating from the Netherlands (where it is also native) and measured parasitoid performance as a proxy for host resistance against parasitism. Pupal mortality, immature development times, and adult biomass of P. xylostella differed significantly across populations when feeding on the same host plant species. In addition, parasitism success differed in terms of parasitoid adult emergence and their biomass, but not their development times. Variation among natural populations of insects should be considered more when studying interactions between plants and insects up the food chain. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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19 pages, 2978 KiB

Open AccessArticle

Geographic and Ecological Dimensions of Host Plant-Associated Genetic Differentiation and Speciation in the Rhagoletis cingulata (Diptera: Tephritidae) Sibling Species Group

by Meredith M. Doellman, Hannes Schuler, Gilbert Jean Saint, Glen R. Hood, Scott P. Egan, Thomas H.Q. Powell, Mary M. Glover, Daniel J. Bruzzese, James J. Smith, Wee L. Yee, Robert B. Goughnour, Juan Rull, Martin Aluja and Jeffrey L. Feder

Insects 2019, 10(9), 275; https://doi.org/10.3390/insects10090275 - 29 Aug 2019

Cited by 10 | Viewed by 3841

Abstract

Ascertaining the causes of adaptive radiation is central to understanding how new species arise and come to vary with their resources. The ecological theory posits adaptive radiation via divergent natural selection associated with novel resource use; an alternative suggests character displacement following speciation in allopatry and then secondary contact of reproductively isolated but ecologically similar species. Discriminating between hypotheses, therefore, requires the establishment of a key role for ecological diversification in initiating speciation versus a secondary role in facilitating co-existence. Here, we characterize patterns of genetic variation and postzygotic reproductive isolation for tephritid fruit flies in the Rhagoletis cingulata sibling species group to assess the significance of ecology, geography, and non-adaptive processes for their divergence. Our results support the ecological theory: no evidence for intrinsic postzygotic reproductive isolation was found between two populations of allopatric species, while nuclear-encoded microsatellites implied strong ecologically based reproductive isolation among sympatric species infesting different host plants. Analysis of mitochondrial DNA suggested, however, that cytoplasmic-related reproductive isolation may also exist between two geographically isolated populations within R cingulata. Thus, ecology associated with sympatric host shifts and cytoplasmic effects possibly associated with an endosymbiont may be the key initial drivers of the radiation of the R. cingulata group. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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15 pages, 2579 KiB

Open AccessArticle

Optical Modelling and Phylogenetic Analysis Provide Clues to the Likely Function of Corneal Nipple Arrays in Butterflies and Moths

by Adrian Spalding, Katie Shanks, Jon Bennie, Ursula Potter and Richard ffrench-Constant

Insects 2019, 10(9), 262; https://doi.org/10.3390/insects10090262 - 22 Aug 2019

Cited by 5 | Viewed by 4162

Abstract

The lenses in compound eyes of butterflies and moths contain an array of nipple-shaped protuberances, or corneal nipples. Previous work has suggested that these nipples increase light transmittance and reduce the eye glare of moths that are inactive during the day. This work builds on but goes further than earlier analyses suggesting a functional role for these structures including, for the first time, an explanation of why moths are attracted to UV light. Using a phylogenetic approach and 3D optical modelling, we show empirically that these arrays have been independently lost from different groups of moths and butterflies and vary within families. We find differences in the shape of nipples between nocturnal and diurnal species, and that anti-glow reflectance levels are different at different wave-lengths, a result thereby contradicting the currently accepted theory of eye glow for predator avoidance. We find that there is reduced reflectance, and hence greater photon absorption, at UV light, which is probably a reason why moths are attracted to UV. We note that the effective refractive index at the end of the nipples is very close to the refractive index of water, allowing almost all the species with nipples to see without distortion when the eye is partially or completely wet and providing the potential to keep eyes dry. These observations provide a functional explanation for these arrays. Of special interest is the finding that their repeated and independent loss across lepidopteran phylogeny is inconsistent with the explanation that they are being lost in the ‘higher’, more active butterflies. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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22 pages, 2679 KiB

Open AccessArticle

Mitochondrial Gene Sequence (COI) Reveals the Genetic Structure and Demographic History of Lymantria dispar (Lepidoptera: Erebidae: Lymantriinae) in and around China

by Yao Xu, Sufang Zhang, Hongbin Wang, Mei Wang and Guohong Li

Insects 2019, 10(5), 146; https://doi.org/10.3390/insects10050146 - 22 May 2019

Cited by 12 | Viewed by 4298

Abstract

The gypsy moth, Lymantria dispar, is among the most destructive quarantine pests of forests. Here, we reconstructed the genetic structure and determined the population differentiation of gypsy moths across its distribution range at different times. This information could be used to both improve the prevention and detection of gypsy moths in the field. Using 31 newly designed species-specific primers targeting fragments of 216–1102 bp, we identified 103 full-length cytochrome oxidase subunit I (COI) gene sequences from eight fresh samples and 95 L. dispar specimens collected between 1955 and 1996, mainly in China. Combining 103 full-length COI gene sequences with 146 COI gene sequences from Genbank or DNA barcode libraries, we analyzed the genetic differentiation, gene flow and haplotypes between gypsy moth populations in order to reflect the genetic structure and population dynamics of gypsy moths. We discovered 25 previously unknown haplotypes from old gypsy moth specimens. We found that the genetic diversity among gypsy moth populations (collected in the same region at different time points) was relatively high. Furthermore, the genetic structure of Chinese geographical populations (Heilongjiang, Liaoning, Beijing) in different years was distinct. Our results suggested that some gypsy moths in China showed the genetic affinity with European gypsy moths (a sub-species of gypsy moths found mainly in Europe). Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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Review

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21 pages, 1279 KiB

Open AccessReview

Use of DNA Markers for Grape Phylloxera Population and Evolutionary Genetics: From RAPDs to SSRs and Beyond

by Javier Tello and Astrid Forneck

Insects 2019, 10(10), 317; https://doi.org/10.3390/insects10100317 - 25 Sep 2019

Cited by 14 | Viewed by 4119

Abstract

Grape phylloxera (Daktulosphaira vitifoliae Fitch) is a major pest of cultivated grapevines (Vitis spp.), occurring in virtually all viticultural regions around the world. Different grape phylloxera strains can be found at varying levels on leaves and roots on both own-rooted plants and in plants grafted onto partially resistant rootstocks. Considering its relevance for the adequate management of the pest in infested vineyards, the analysis of its genetic diversity has received considerable attention from the scientific community in the last decades. Here, we review 25 years of DNA-based molecular markers applied to the analysis of the genetic structure and the reproductive mode of grape phylloxera in its native range and in different introduced regions. The use given to RAPD, AFLP, mtDNA sequencing and microsatellite (SSR) genetic markers for the analysis of grape phylloxera diversity is discussed, and an overview of the main findings obtained after their application to different populations collected in diverse regions all around the world is shown. Lastly, we explore how recent advancements in molecular biology and in modern high throughput genotyping technologies may be applied to better understand grape phylloxera natural diversity at a molecular level. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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25 pages, 3161 KiB

Open AccessReview

Neo Sex Chromosomes, Colour Polymorphism and Male-Killing in the African Queen Butterfly, Danaus chrysippus (L.)

by David A.S. Smith, Walther Traut, Simon H. Martin, Piera Ireri, Kennedy S. Omufwoko, Richard ffrench-Constant and Ian J. Gordon

Insects 2019, 10(9), 291; https://doi.org/10.3390/insects10090291 - 9 Sep 2019

Cited by 8 | Viewed by 5850

Abstract

Danaus chrysippus (L.), one of the world’s commonest butterflies, has an extensive range throughout the Old-World tropics. In Africa it is divided into four geographical subspecies which overlap and hybridise freely in the East African Rift: Here alone a male-killing (MK) endosymbiont, Spiroplasma ixodetis, has invaded, causing female-biased populations to predominate. In ssp. chrysippus, inside the Rift only, an autosome carrying a colour locus has fused with the W chromosome to create a neo-W chromosome. A total of 40–100% of Rift females are neo-W and carry Spiroplasma, thus transmitting a linked, matrilineal neo-W, MK complex. As neo-W females have no sons, half the mother’s genes are lost in each generation. Paradoxically, although neo-W females have no close male relatives and are thereby forced to outbreed, MK restricts gene flow between subspecies and may thus promote speciation. The neo-W chromosome originated in the Nairobi region around 2.2 k years ago and subsequently spread throughout the Rift contact zone in some 26 k generations, possibly assisted by not having any competing brothers. Our work on the neo-W chromosome, the spread of Spiroplasma and possible speciation is ongoing. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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15 pages, 334 KiB

Open AccessConcept Paper

Generalism in Nature…The Great Misnomer: Aphids and Wasp Parasitoids as Examples

by Hugh D. Loxdale, Adalbert Balog and Jeffrey A. Harvey

Insects 2019, 10(10), 314; https://doi.org/10.3390/insects10100314 - 24 Sep 2019

Cited by 13 | Viewed by 2935

Abstract

In the present article we discuss why, in our view, the term ‘generalism’ to define the dietary breadth of a species is a misnomer and should be revised by entomologists/ecologists with the more exact title relating to the animal in question’s level of phagy—mono-, oligo, or polyphagy. We discard generalism as a concept because of the indisputable fact that all living organisms fill a unique ecological niche, and that entry and exit from such niches are the acknowledged routes and mechanisms driving ecological divergence and ultimately speciation. The term specialist is probably still useful and we support its continuing usage simply because all species and lower levels of evolutionary diverge are indeed specialists to a large degree. Using aphids and parasitoid wasps as examples, we provide evidence from the literature that even some apparently highly polyphagous agricultural aphid pest species and their wasp parasitoids are probably not as polyphagous as formerly assumed. We suggest that the shifting of plant hosts by herbivorous insects like aphids, whilst having positive benefits in reducing competition, and reducing antagonists by moving the target organism into ‘enemy free space’, produces trade-offs in survival, involving relaxed selection in the case of the manicured agro-ecosystem. Full article

(This article belongs to the Special Issue Cutting-Edge Evolution of Insects: Factors Governing Ecological Divergence of Natural Populations Assessed Using Molecular and Genetic Markers)

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