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Wikipedia: Boll weevils (politics)
Boll weevils was an American political term used in the mid- and late-20th century to describe conservative Southern Democrats.
 
During and after the administration of Franklin D. Roosevelt, conservative southern Democrats were part of the coalition generally in support of Roosevelt’s New Deal and Harry Truman’s Fair Deal economic policies, but were opposed to desegregation and the American civil rights movement. On several occasions between 1948 and 1968, a prominent conservative Southern Democrat broke from the Democrats to run a third party campaign for President on a platform of states’ rights: Strom Thurmond in 1948, Harry F. Byrd in 1960, and George Wallace in 1968. In the 1964 presidential election, 5 states in the Deep South (then a Democratic stronghold) voted for Republican Barry Goldwater over Southern Democrat Lyndon B. Johnson, partly due to Johnson’s support of the Civil Rights Act of 1964 and Goldwater’s opposition to it. After 1968, with desegregation a settled issue, the Republican Party began a strategy of trying to win conservative Southerners away from the Democrats and into the Republican Party (see Southern strategy and Silent Majority).

Nonetheless, a bloc of conservative Democrats, mostly Southerners, remained in the United States Congress throughout the 1970s and 1980s (Conservative Coalition). These included Democratic House members as conservative as Larry McDonald, who was also a leader in the John Birch Society. During the administration of Ronald Reagan, the term “boll weevils” was applied to this bloc of conservative Democrats, who consistently voted in favor of tax cuts, increases in military spending, and deregulation favored by the Reagan administration.
 
“Boll weevils” was sometimes used as a political epithet by Democratic Party leaders, implying that the boll weevils were unreliable on key votes or not team players.
 
Most of the boll weevils eventually retired from office, or in the case of some such as Senators Phil Gramm and Richard Shelby, switched parties and joined the Republicans. Since 1988 the term boll weevils has fallen out of favor. A bloc of conservative Democrats in the House, including some younger or newer members as well as the remaining boll weevils who refused to bow to pressure to switch parties, organized themselves as the Blue Dogs in the early 1990s. A different bloc of Democrats also emerged in the 1990s, under the Democratic Leadership Council (DLC), espousing conservative pro-business views on economic issues and moderate views on social issues
   
Google Books
The Assault of Laughter:
A treasury of American political humor
By Arthur Power Dudden
New York, NY: T. Yoseloff
1962
Pg. 478:
It was Mr. Joe Tumulty, then secretary to Woodrow Wilson, who first described as boll weevils the new Southern Congressmen and deserving Democrats from below the line, but out of consideration for his position he was not charged with it at the time.
 
Google Books
Safire’s Political Dictionary
By William Safire
New York, NY: Oxford University Press
2008
Pg. 69:
boll weevil A Southern conservative Democrat.
(...)
The name of this Southern pest became a self-applied label by conservative Democrats in the 1950s. During Eisenhower’s Administration, Rep. Howard Smith of Virginia and, later, Rep. Omar Burleson of Texas advanced the boll weevil as the symbol of their unstoppable group.
 
In the 1980s, Rep. Charles Stenholm,  a Democrat from Texas, reapplied the term, linking himself with other tenacious conservative Democrats.