Genetic GPS for Tracking Boll Weevils

Fortunately, the boll weevil (Anthonomus grandis), which devastated U.S. cotton crops for much of the 20th century, is now found only in parts of the mid-South and South Texas, thanks to eradication efforts. But monitoring weevils to keep track of where they are coming from—and where they’re going—is vital for protecting cotton crops in the United States.

Agricultural Research Service (ARS) entomologist Tom Sappington works in the ARS Corn Insects and Crop Genetics Research Unit at Ames, Iowa. He has tracked local weevil movements by marking the insects with enamel paint or fluorescent powders and recapturing them later. Now he uses “microsatellites”—short, repetitive DNA sequences—and population assignment tests to find out where weevils in different populations have come from. These tests help pinpoint the migratory patterns and origins of boll weevils over long distances.

Of course, the weevils don’t respect international borders. In 2004, a small group of boll weevils was found next to an eradication zone in Durango, Mexico, where weevils had not been reported for about 10 years. Sappington compared weevil microsatellites from this group to four other weevil populations from northern Mexico and southern Texas.

His analysis determined that some of the weevils in this group were immigrants. But most of them belonged to a previously undetected resident population that had suddenly increased because of greater rainfall levels. His findings also indicated that final weevil eradication efforts in Texas were being hindered by weevil migration within Texas and from Mexico.

Sappington’s work demonstrates that powerful microsatellite markers and population assignment tests are practical tools for identifying the origins of boll weevils found in areas that have previously been weevil-free. In addition, identifying boll weevil migrants within established weevil populations and knowing where these new migrants came from will foster better strategies for monitoring and managing boll weevil pest introductions throughout North America.

Read more about this research in the August issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.