RÍO BRAVO, Mexico — It has bedeviled the United States for more than a century, becoming a bane of the American South, causing widespread job losses and setting off countless debates about stopping migration from Latin America.

This is a wave that even the biggest, most expensive wall might never hold back.

We’re talking about the boll weevil.

It is just one of the many issues that rely on bilateral cooperation between the United States and Mexico, and it embodies, in microcosm, many of the essential qualities of the broader relationship between the two countries: an alliance bordering on codependence despite economic, political and cultural differences.

Thought to be native to Mexico and Central America, the boll weevil is a beetle that attacks cotton plants. It first crossed into the United States in the 1890s around Brownsville, Tex., and quickly spread to the Atlantic Seaboard, nearly wiping out the cotton industry.