Indeed some intriguing facts on these fascinating animals. However, most importantly Aphids are small insects that are often transported around the globe, constituting an invasive threat to native and cultivated plants. Actually they are considered one of the most serious agricultural pests of temperate regions because they cause direct damage by feeding on phloem and because they can act as vectors of many plant viruses.
Unfortunately, the range of continuous morphological variation in aphids is probably wider than in any other insect group which makes any accurate identification very difficult. Researchers also know of the occurrence of different morphs on different host plants and at different times in the year. A number of genera can't be identified by using morphology alone. Researchers need to include information on host-plant association to arrive at an accurate identification. There are also considerable gaps in our knowledge which is e.g. illustrated by the fact that for the genus Aphis, no taxonomist has yet succeeded in writing a comprehensive dichotomous morphological key that effectively separates all the species of a given local fauna.
A new study by a group of French researchers from the Centre de Biologie pour la Gestion des Populations (CBGP) and the Institut national de la recherche agronomique (INRA) is now showing how to use DNA Barcoding to overcome these obstacles. They created the first European aphid barcode database including about 274 species:
These data confirm that COI barcoding is a useful identification tool for aphids. Barcode identification is straightforward and reliable for 80% of species, including some difficult to distinguish on the basis of morphological characters alone. Unsurprisingly, barcodes often failed to distinguish between species from groups for which classical taxonomy has also reached its limits, leading to endless revisions and discussions about species and subspecies definitions. In such cases, the development of an effective procedure for the accurate identification of aphid specimens continues to pose a difficult challenge.
The authors also suggest to establish a host-plant herbarium linked to aphid voucher specimens, which would allow the confirmation of aphid species identification when aphid morphology is not sufficient. Aphid taxonomists are, by necessity, also “amateur” botanists, they are not specialists in plant systematics. In situations in which the identification of the aphid is dependent on correct host-plant identification, the frequency of misidentification may be increased further. Once both aphid species and host plant species have a proper DNA Barcode designation they can be used for future reference.