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Leafminers Identified Faster


Two leafmining flies—Liriomyza huidobrensis and L. langei—are pests of many vegetable and flower crops, including peas, beans, melons, onions, tomatoes, potatoes, celery, garlic, lettuce, chrysanthemums, and carnations. Their larvae tunnel inside leaves and other plant parts as they feed, leaving winding trails called mines that are visible through the leaf surface.

During outbreaks, these insects can cause severe damage, resulting in substantial economic losses. Originally present only in the western United States and South America, they have now invaded Europe, the Middle East, and Asia.

L. huidobrensis and L. langei are so similar in form and structure that they were once considered to be one species. But ARS molecular biologist Sonja Scheffer and biological sciences technician Matthew Lewis used DNA sequence data from mitochondrial and nuclear genes to show that there are actually two species. DNA data also showed that the invasive leafminers causing extensive crop damage around the world are L. huidobrensis, not L. langei. Currently, the highly invasive L. huidobrensis is not known to be present in the United States.

Using DNA sequence data is an expensive, time-consuming way to identify species. Now Scheffer has refined a less expensive, faster molecular method to differentiate the two pests. It uses polymerase chain reaction combined with restriction fragment length polymorphism (PCR-RFLP) analysis. This method can be used with adult, larval, or pupal leafminer specimens. It was developed to provide researchers, pest managers, and quarantine officers with a simple and quick molecular method to differentiate L. langei from L. huidobrensis.

In early 2000, Scheffer confirmed the accuracy of PCR-RFLP by applying it to 31 fly specimens for which DNA sequence data had clearly identified the species. She tested 52 more specimens from recently introduced leafminer populations in Sri Lanka, South Africa, and Canada and found all to be L. huidobrensis.

PCR-RFLP can be performed by anyone with access to a laboratory that has a PCR thermocycler and associated paraphernalia—an increasingly common piece of equipment.

"The entire set of procedures—from DNA extraction to final identification—can be completed within a single working day," says Scheffer, "compared to several days and additional expense for DNA sequencing."

But there's more opportunity for misidentification with this method than with sequence data, because PCR-RFLP banding patterns may be shared by multiple species. For this reason, it is appropriate to use a particular PCR-RFLP test only with those species for which the test was developed.—By Jennifer Arnold, formerly with ARS.

Sonja Scheffer is with the USDA-ARS Systematic Entomology Laboratory, Bldg. 011A, 10300 Baltimore Ave., Beltsville, MD 20705-5129; phone (301) 504-5317, fax (301) 504-6482.


"Leafminers Identified Faster" was published in the July 2002 issue of Agricultural Research magazine.


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