Crop protection | Obtaining genetic markers for various insects would speed identification and help determine the best crop protection method

LINDELL BEACH, B.C. — Understanding insect diets can eat up a lot of a researcher’s time as they try to observe behaviour and document what they find.


Having a means to more quickly identify a particular insect feeding on a farmer’s valuable crop can also speed up diagnoses and develop quicker responses to fight the bugs. 


New genetic techniques that develop what researchers call a genetic barcode, small DNA regions within an organism’s genome, could soon be available to provide speedier identification.


Scientists with the Smithsonian Institution recently developed DNA extraction techniques to profile the DNA inside the stomachs of 20 species of rolled leaf beetles in Costa Rica and to study 33 species of flowering plants in the ginger and banana order zingiberales on which the beetles eat and lay their eggs. 


Carlos Garcia-Robledo, a post-doctoral fellow at the Smithsonian and lead author of the study published in the journal PLOS ONE, said the new method improves understanding of the interrelationships between plants and insects.


Researchers extracted not only DNA from the stomachs, but also from the actual insects, then used DNA markers to specify each insect and each plant to profile the diet.


After extracting the DNA, re-searchers used baseline data gathered through years of field observation to test the accuracy of the DNA method.


Garcia-Robledo said the study was designed to confirm a methodology that would be efficient and time-effective for environmental management and for the management and protection of valuable commercial crops. 


“Scientists proposed several DNA barcodes, as not every gene works for all plant groups. The first step is to determine if a given DNA barcode works for the plant group of interest. After identifying (the DNA barcode), it is possible to understand the diets of a whole community of insects. In habitats of difficult access, such as the forest canopy, this method will prove invaluable.”


Two years ago, the need for a quick identification method became apparent with the appearance of an insect in the fruit growing region of Washington state. 


An unrecognized fruit fly was found feeding on crabapples in Kennewick close to the heart of Washington’s $1.5 billion apple-growing region. 


The discovery was alarming be-cause of the possibility that a fruit fly not associated with crabapples had expanded its usual diet to include the fruit. 


It also raised the question about the dietary expansion of other flies known to be pests, in particular the invasive apple maggot fly.


Larvae of the fruit fly feeding on crabapples were sent to research entomologists at the U.S. Department of Agriculture’s Yakima Agricultural Research Laboratory in Wapato, Wash., where they were raised over four months to adulthood and visually identified as rhagoletis indifferens.


One larva was sent to the University of Notre Dame in Indiana, where within two days biological sciences professor Jeffrey Feeder identified it through genetic analysis as the same species. 


“R. indifferens is a major pest of sweet and sour cherries in Washington and Oregon but is not of concern to apple growers, and no R. indifferens has been reared from apple,” he said.


“The crabapples are smaller and more like cherries, so it is easier to see how R. indifferns may have chosen to oviposit (lay eggs) into it. So while we cannot rule out the possibility that the cherry fly could someday switch to apple, it is not of relatively great concern.”


The observation of the changing diet of the cherry fly is a concern to watch for in a range of invasive, problematic insects such as the apple maggot fly.


“Right now, the apple maggot has not been reared from a commercial orchard, but it is beginning to en-croach nearer to them,” said Feder. 


The expansion of the apple maggot fly includes the B.C. Lower Mainland and Vancouver Island and concerns are growing that it might spread to the commercial apple growing regions in the Interior.


The refinement of the DNA barcodes allows identification not only from the insects themselves, but from their eggs and larvae.


“In addition to plant DNA barcodes, we also obtained for each beetle the animal DNA barcode CO1,” said Garcia-Robledo. 


“Using this DNA barcode, it is possible to determine the species of eggs and larvae. These results will be published soon.”


He said other laboratories are interested in using the methods developed at Smithsonian. 


“These methods can be used to determine, for example, if an adult insect found in a crop field is actually feeding on a plant and also to associate eggs and larvae with adults. This information is fundamental for any integrated pest management program.”