New Technique May Help Farmers Identify the European Corn Borer
By Ed Ricciuti
Farmers who need to control the destructive European corn borer (Ostrinia nubilalis) may soon be able to distinguish it from look-alike species by simply scanning an image of its wing into a computer and pecking a few keys. A technique developed by Polish scientists marks the first time that measurements of key structural features in the wing have been used to identify the borer, potentially a major advance in controlling the pest.
The method was developed by Lukasz Przybylowicsz, Michal Pniak, and Adam Tofilski, and it is described in an article in the Journal of Economic Entomology.
The new identification technique may have important implications for integrated pest management (IPM), a system of controlling pests that combines a variety of tools, ranging from biological to chemical, with focus on managing the ecosystem. Successful application of IPM starts with monitoring the environment for damage and hinges on identifying the pests that are causing it.
“Quick, easy, and precise identification of the pest” is critical if a farmer wishes to use IPM, the authors wrote. “Most farmers are not able to identify the imago [adult] of the European corn borer and especially to distinguish it from other species.” In fact, it usually takes specialists to do the job.
Fast, on-site identification is essential because many IPM methods depend on hitting the pest at times in its life cycle when it is most vulnerable. The release of parasitic wasps of the genus Trichogramma, for example, must coincide with the time when the borer begins to lay eggs.
The experiments show that people who are unschooled in taxonomy and pest identification can easily identify the borer and other pest species of moth as long as they have access to “automatic computer equipment” and the appropriate software. However, the method still needs a bit of fine tuning and tweaking, according to the authors. More studies of the borer’s geographical subspecies and of related species are needed to complete the information required for accurate identification of the borer throughout its range.
The European corn borer is a prime pest on corn but also impacts more than 200 other crops, by some estimates causing up to $2 billion in damage annually in the United States alone. So far confined mostly to the east of the Rocky Mountains, the borer first showed up in Massachusetts in 1917. It may have reached North America in shipments of broom corn, and perhaps millet from Europe. It is widespread there and in much of Asia and North Africa.
Fully grown larvae overwinter in the lower stem and other remains of plants on which they feed. They pupate in spring, and emerge as adult moths in May and June. One to three times a season, mature females lay white eggs clumped on the undersides of the lower leaves of host plants. The second generation generally causes the most damage because it targets pollinating corn. Eggs hatch within a week. Inch-long caterpillars, pinkish with a dark head, chew their way into host plants, upsetting the movement of nutrients and water, damaging corn ears, and sometimes causing them to drop. After three to four weeks, the caterpillars pupate within the ears and emerge as adults in early summer and resume the reproductive cycle.
The wings of the adult, which span an inch, are yellowish-brown with lateral wavy dark bands. Females are slightly larger and lighter than males. To the unpracticed eye, it seems a rather nondescript moth, easy to confuse with some others, especially members of its own family, Crambidae.
The scientists used light traps to collect three species of Crambidae — Anania hortulata, Sitochroa verticalis and Pleuroptya ruralis — in north, east, and central Poland to compare them with the adult borer. All of them are found in corn fields at the same time as the borer, and all have somewhat similar coloration and markings on the wings.
The identification method developed by the scientists focuses on the arrangement of veins in the wings of the moths, applying a technique known as geometric morphometry. Essentially, it examines and compares the geometry of an organism’s structures — in other words, where its parts are positioned in relation to one another. Computerized statistical analysis is key to attaining results.
After scales on the wings were removed with a soft brush, the wings were mounted on glass photographic frames and scanned. The researchers selected nine points — called “landmarks” — at junctions of veins in the central part of the wing. Landmarks, such as where veins join, are a common feature among species. A mass of geometrical information based on coordinates of the landmarks was then entered into software used for identification, and when the shape of wing venation was compared, significant differences were seen between species. The accuracy of the test was 97 percent.
Ideally, according to the authors, a farmer should be able to collect suspect moths in a light trap, toss the ones that bear no resemblance to the adult borer, and retain the remaining specimens for further identification. Wings from the suspects would then be mounted and scanned. The nine landmarks would be marked on the image so software can separate the borers from other species.
Before farmers can be sure of results, the scientists note, the results “should be confirmed by further studies.” Additional studies would include repeating the experiment on larger samples of insects. Once that is done, the researchers say, “this method can be used by farmers to identify this pest and apply control measures at optimal time.”
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Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.