A 658-bp fragment of mitochondrial DNA from the 5' region of the mitochondrial cytochrome c oxidase 1 (COI) gene has been adopted as the standard DNA barcode region for animal life. In this study, we test its effectiveness in the discrimination of over 300 species of aphids from more than 130 genera. Most (96%) species were well differentiated, and sequence variation within species was low, averaging just 0.2%. Despite the complex life cycles and parthenogenetic reproduction of aphids, DNA barcodes are an effective tool for identification.

Summary 1. Aphids are notorious pests of world agriculture. Even so, uncertainty persists as to their capacity for successful aerial dispersal. Evidence exists that, under some conditions, aphids can be wind‐borne over long distances, i.e. hundreds of kilometers over desert or sea. It has been argued, in the recent past, that this phenomenon may be part of a strategy to locate fresh host plants in new distant areas. However, the proportion of these insects successfully colonizing new hosts is unknown. 2. Other work using meteorological backtracking has also indicated long‐distance movement, but the accuracy of such predictions is dubious unless the altitude of transport is known. Mark‐releaseecapture experiments with such small insects have limited potential due to large dilution effects. Static ‘snap‐shots’ of demographic population densities, using suction traps, cannot accurately distinguish local aerial density fluxes and population movements from a distance. However, genetic and physiological markers may provide more direct information on population mixing; for example, some allozyme studies have shown a limited level of inter‐population gene flow. 3. Under suitable conditions, aphids take off, maintain flight and alight in response to the appropriate visual and olfactory cues. Undoubtedly successful long‐distance movement occurs from time to time, but its ecological relevance may have been overstated in the past. It may be selectively disadvantageous for aphids to move from areas containing their host plants. In contrast, it is advantageous for aphids to maximise their chances of survival and reproductive success by landing on suitable plant hosts at the earliest opportunity. 4. The clonal nature of aphids (a single genotype may comprise vast numbers of individuals) means that there may be advantages to phenotypic variation between individuals in the readiness to move. Recent evidence indicates that such a variation exists in the duration of the behavioural migratory phase, the initial period of maiden flight when host‐plant cues are ignored and when landing is inhibited. 5. The relative biological importance of short‐ us. long‐distance movements is reassessed with reference to plant virus epidemiology and the spread of new genotypes, e.g. insecticide resistance. It is concluded that the biological relevance of short‐distance movements have a much greater impact on population and genotype distribution than long‐distance movements, which may be comparatively infrequent.

BackgroundDNA barcoding, the analysis of sequence variation in the 5′ region of the mitochondrial cytochrome c oxidase I (COI) gene, has been shown to provide an efficient method for the identification of species in a wide range of animal taxa. In order to assess the effectiveness of barcodes in the discrimination of Heteroptera, we examined 344 species belonging to 178 genera, drawn from specimens in the Canadian National Collection of Insects.Methodology/Principal FindingsAnalysis of the COI gene revealed less than 2% intra-specific divergence in 90% of the taxa examined, while minimum interspecific distances exceeded 3% in 77% of congeneric species pairs. Instances where barcodes fail to distinguish species represented clusters of morphologically similar species, except one case of barcode identity between species in different genera. Several instances of deep intraspecific divergence were detected suggesting possible cryptic species.Conclusions/SignificanceAlthough this analysis encompasses 0.8% of the described global fauna, our results indicate that DNA barcodes will aid the identification of Heteroptera. This advance will be useful in pest management, regulatory and environmental applications and will also reveal species that require further taxonomic research.

The Adelgidae form a small clade of insects within the Aphidoidea (Hemiptera) that includes some of the most destructive introduced pest species threatening North American forest ecosystems. Despite their importance, little is known about their evolutionary history and their taxonomy remains unresolved. Adelgids are cyclically parthenogenetic and exhibit multigeneration complex life cycles. They can be holocyclic, with a sexual generation and host alternation, or anholocyclic, entirely asexual and without host alternation. We discuss adelgid behavior and ecology, emphasizing plant-insect interactions, and we explore ways that the biogeographic history of their host plants may have affected adelgid phylogeny and evolution of adelgid life cycles. Finally, we highlight several areas in which additional research into speciation, population genetics, multitrophic interactions, and life-history evolution would improve our understanding of adelgid biology and evolution.

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