Monday, October 22, 2012

Enemy of wine

The Grape is perhaps the most economically important crop in Chile, with vineyards covering over 180,000 hectares in 2007, and about a third of production dedicated to table grapes. This crop accounts for about 42% of all fruit exports in Chile. The country is also the fifth largest exporter of wines in the world, and the ninth largest producer.

Mealybugs (Pseudococcidae) is the common name for some among the most destructive plant pests. They are scale insects coated with a powdery mealy waxy secretion; that feed on plant juices. Mealybugs are considered pests on many plants, including apple, avocado, cassava, citrus, coffee, grapes, pineapple, rice and sugarcane. The main phytosanitary problem for international sales of Chilean table grapes are mealybugs, e.g. 71.5% of all table grape rejections during inspections before export have been attributed to these tiny scale insects. They also deposit honeydew on the fruit, on which sooty mold subsequently develops
Correct identification is essential when dealing with species considered as pests. Insecticide applications have to be timed properly because different species occupying the same host may have different biological characteristics. Furthermore, natural enemies of mealybugs tend to specialize on particular species.  Therefore, any biological control program relies on proper identification of the mealybugs present. Another problem is that in international trade, different markets identify different mealybug species as quarantine pests. However, scale insects are not so easy to identify and mealybugs comprise over 2000 species!

Chilean researchers have now used DNA Barcoding to identify the most common mealybug species in their country thereby establishing a DNA library that will help for future inspections and studies. They could show that  Pseudococcus viburni, Pseudococcus meridionalis and Pseudococcus cribata are the main pest species of grapes in Chile's main grape production area. The genetic variability of Pseudococcus viburni and Pseudococcus cribata, at two molecular markers used (COI and ITS), suggest that they are either native or long-established in the region. In contrast, no genetic variability was found in Pseudococcus meridionalis, suggesting that this species may have been recently introduced to Chile.

This was already the second study on these pest species and given their importance for fruit production it certainly won't be the last one. Another group had looked at the potential of DNA Barcoding for species in France and Egypt.

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