Due to their role in the transmission of diseases, it is important to be able to determine which species of insect are present in a particular area. Vector borne diseases are transmitted by a limited range of vector species, so recognizing, for instance, which species of Anopheles mosquitoes are found allows field entomologists to implicate the species in malaria transmission, and tests can then be done to determine the infection status of captured individual mosquitoes.

Classification by morphology
The traditional method used to identify species is based on morphological characteristics. Using a dissecting microscope or hand lens it is possible to examine fine features such as the shape and colouration of the abdomen or the pattern of veins on the wings. Specialised body parts such as the cerci, a pair of sensory appendages located at the back of the abdomen, and tarsi, the bottom portion of an insect’s leg, are also features used in identification. 

Taxonomic classification can be made using taxonomy keys. The first classification that is made for insects in the taxonomic order. Mosquitoes belong to the Diptera, an order than includes an estimated 1 million species including house flies, hover flies, crane flies, Tsetse flies and other insects that have just a single pair of wings. Triatomine bugs, which transmit Chagas disease, belong to the Hemiptera, an order of true bugs. Other insects within the Hemiptera include cicadas, aphids, planthoppers, leafhoppers, and shield bugs. Taxonomic keys allow further identification at the family, subfamily, genus and species level.

Classification using genetic techniques
The identification of specimens collected in the field as part of disease surveillance programmes can be particularly challenging if specimens are poorly preserved or if there are many species in an area that have similar physical characteristics. Even for experts in this field, the adults of some species remain difficult to identify morphologically. More modern approaches to species identification can make use of genetic differences between species; DNA can be extracted from recently-collected or preserved specimens using commercially available kits, and polymerase chain reaction (PCR) techniques allow the DNA in regions of interest to be amplified and analysed. These approaches rely on fixed, characterized differences in the DNA sequences of different species^[1]. For example, members of the Anopheles minimus group can be distinguished more simply, rapidly and accurately using genetic techniques^[2] than through morphological classification.

References

1. Higa Y, Toma T, Tsuda Y, Miyagi I. A multiplex PCR-based molecular identification of five morphologically related, medically important subgenus Stegomyia mosquitoes from the genus Aedes (Diptera: Culicidae) found in the Ryukyu Archipelago, Japan. Japanese journal of infectious diseases. 2010;63(5):312-6. 
   http://naosite.lb.nagasaki-u.ac.jp/dspace/bitstream/10069/24511/1/JJID63_312.pdf
   
   
2. Phuc, A. et al., 2003. Multiplex PCR assay for malaria vector Anopheles minimus and four related species in the Myzomyia Series from Southeast Asia. Medical and Veterinary Entomology 17: 423–428. 
   https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2915.2003.00462.x