Monday, November 25, 2013

Black flies

Black flies are members of the fly family Simuliidae. To date over 1,800 species of black flies are known. Most species belong to the large genus Simulium. Most black flies feed on the blood of mammals, including humans, although the males feed mainly on nectar. The ones feeding on human blood are a nuisance as the insects use their very short mouthparts that are sharp enough to cut into the flesh of their victim and lick the blood that comes out. A blood meal lasts about 3-6 minutes and can even go to 15 minutes. During this meal, a female eats as much blood as its own weight. In order to make the process more effective the insect injects saliva and an anticoagulant. The latter causes swelling and itching, and I can attest that the latter is really a nuisance. Also unlike the mosquito, black flies attack in silence without a distinct buzz.
Black flies are small insects, black or gray, with short legs, and antennae. They are known to spread several diseases, including river blindness in Africa and the (Central and South ) Americas.

Black flies are a nightmare for traditional taxonomy because of their small size and structural homogeneity. Banding patterns of the polytene chromosomes (cytotypes) have been the standard in addressing this challenge, but require experienced people to interpret them and typically are workable only for certain larva stages. 

Two researchers have now examined the efficiency of DNA Barcoding for differentiating morphospecies and cytoforms of species complexes occurring in Thailand:

A total of 351 cytochrome c oxidase subunit 1 sequences were obtained from 41 species in six subgenera of the genus Simulium in Thailand. Despite high intraspecific genetic divergence (mean = 2.00%, maximum = 9.27%), DNA barcodes provided 96% correct identification. Barcodes also differentiated cytoforms of selected species complexes, albeit with varying levels of success. Perfect differentiation was achieved for two cytoforms of Simulium feuerborni, and 91% correct identification was obtained for the Simulium angulistylum complex. Low success (33%), however, was obtained for the Simulium siamense complex. The differential efficiency of DNA barcodes to discriminate cytoforms was attributed to different levels of genetic structure and demographic histories of the taxa. DNA barcode trees were largely congruent with phylogenies based on previous molecular, chromosomal and morphological analyses, but revealed inconsistencies that will require further evaluation.

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