Monday, July 29, 2013

Book lice and DNA Barcoding

Psocids (Psocoptera) are small, soft-bodied insects and are now considered significant pests of stored products. They can persist on a variety of foods, and there is variation in biology and ecology among the different species. Psocids are tiny insects that live in damp environments where they eat mold and mildew. They are often called bark lice or book lice. The name bark lice probably comes from the fact that they gather under the bark of trees while the name book lice comes from the fact that they gather on moldy books in damp homes. Experts think that the sizing and starch in the bindings of books supports mold growth in humid environments.

The pest status of stored-product psocids is due to the weight losses caused by consumption of germ and endosperm. As a result commodities infected can be rejected for export. They also have the ability to spread fungal pathogens, thereby making them a human health threat especially through allergic responses they cause in sensitized people.

Recent studies have shown psocids to be quite tolerant to some of the currently used insecticides when applied at rates usually effective for control of other stored-product insect pests, such as Coleoptera and Lepidoptera. Most challenges in psocid control stem from the fact that even very similar species differ in their sensitivity to various insecticides. The problem is that morphological identification is extremely difficult, further hampered by the lack of psocid entomological experts. A good example is the the genus Liposcelis that includes 126 valid species. About 10% of those commonly occur in habitats associated with humans and many have been identified as pest species.

A new study now successfully tested the suitability of DNA-based identification for Liposcelis members using 16S rDNA and DNA Barcoding (COI). Although it is not entirely clear to me why there was a need to use two mitochondrial markers for species identification it certainly worked well. Unfortunately, the authors join the increasing number of people calling e.g. 16S-based species identification DNA Barcoding which it isn't. Remember, DNA Barcoding for most animals is done only with COI and the community went through great lengths in order to define such standards. Well, I won't go on too long as the researchers did COI which is in turn very helpful for all other researchers that like to use DNA Barcoding for more targeted pest control. Given that different Liposcelis pest species respond differently to control measures, DNA Barcoding might be the only suitable method to optimize response.

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