The term Wasp, or WASP, acronym from white Anglo-Saxon Protestant, denotes a person who belongs to, or is thought of, as being part of a white, upper middle-class, northern European, Protestant group that dominates economic, political and cultural activity in the USA.

It might be interesting to note that in the 1920s Charles Lewis Fowler (1877-1974), Baptist minister and educator, used white Anglo-Saxon Protestant when promoting the Ku Klux Klan, an extremist right-wing secret society in the USA; the following is from the Danville Daily Messenger (Danville, Boyle County, Kentucky) of Monday 1^st May 1922:

DR. FOWLER SPEAKS ON PURPOSES OF KLU KLUX KLAN

Representative of American Educational Foundation Addresses Gathering at Court House on “America For Americans Only.”
Denouncing the idea that the Klu Klux Klan was a tar and feather organization and insisting that it was a group of red-blooded citizens that had dedicated on its knees that it will give acceptance to the things that are purely American, Dr. C. Lewis Fowler, representative of the American Educational Foundation, of Atlanta, Ga., addressed a gathering of about sixty Boyle county citizens at the Court House Saturday night on “America for Americans Only.”
[…]
Dr. Fowler […] entered upon the purposes of the Invisible Order of the Knights of the Klu Klux Klan. The purpose of this fraternity, which Dr. Fowler termed “the strangest, the most weird, the most mystical on all the continent is an attempt that is actively being consumated to elicit, to combine, and to direct the entire white, Anglo-Saxon, protestant native born manhood of this America.
He then gave reasons why the organization was excluding certain classes of citizens in this country. He said that the struggles and sorrows of history came from the liberty of ours given to us by our forefathers and urged that these distinctive principles be handed down to our children. The Klu Klux Klan is not fighting anybody; it is simply pro Anglo-Saxon, said Dr. Fowler.
He announced that the Governors of fourteen states, and eighteen United States Senators were members of the sublimest political, social institution in the country—the Klu Klux Klan, which was growing at the rate of 4000 members a day.

The earliest instance of the acronym Wasp that I have found is from The Daily Pantagraph (Bloomington, Illinois) of Thursday 28^th June 1956; in South in Transition: Desegregation Slow, Painful Process, Bill Harris gave an account of a conference that had taken place the previous day at Illinois State Normal University; one of the orators was Arnold Dewald Albright (1913-2009), educator-administrator from the University of Kentucky:

The problem of tensions between peoples is beginning to be more than racial, Mr. Albright said. It is beginning to be reflected in anti-Semitism, anti-Catholicism and anti-laborism.
The Southerner uses the term “WASP” to describe the average southerner — white, Anglo-Saxon, Protestant. He is proud of his Anglo-Saxon parentage. He is inbred.

This quotation seems to imply that the acronym was in common usage in the Southern United States.

In the text containing the second-earliest instance of Wasp that I have found, “in the cocktail party jargon of the sociologists” indicates that the term was at that time also used in the circle of American sociologists; this text is Liberal Democracy and Social Control, by the American political scientist Andrew Hacker (born 1929), published in The American Political Science Review of December 1957:

I. THE CLASS BASIS OF LIBERAL DEMOCRACY

Whether we like to admit it or not, a society which encourages the full flowering of individual liberty is, and can only be, a stratified society. […]
The bulk of the community defers to a small section and does not think to question that this class will hold the important positions and make the vital decisions. America has had such a class, and to it has been delegated national power in its economic, political, and social aspects. These “old” Americans possess, for the most part, some common characteristics. First of all, they are “WASPs”—in the cocktail party jargon of the sociologists. That is, they are white, they are Anglo-Saxon in origin, and they are Protestant (and disproportionately Episcopalian). To their Waspishness should be added the tendency to be located on the Eastern seaboard or around San Francisco, to be prep school and Ivy League educated, and to be possessed of inherited wealth.

Yet another source states that Wasp was in common usage among New York politicians during the same period; the following is from The Greenville News (Greenville, South Carolina) of Monday 13^th October 1958:

WASPS

On our recent safaris into the jungles of New York politics, we have made mention of the “balanced ticket” concept […].
(In case you have forgotten, the “balanced ticket” theory holds that it is absolutely necessary that the political parties nominate at least one man from each of the major racial and religious groups and geographical areas of the state. It subordinates—even ignores—such matters as talent, integrity and past performance in public office.)
We are indebted to The Reporter, a magazine of far left persuasion, for further information on this intriguing subject.
Giving its version of the facts behind the maneuvering by which Carmine De Sapio, boss of Tammany Hall, got the Democratic Party nomination for his man over the choice of Gov. Averell Harriman, The Reporter made use of the term, “Wasp.”
This, the magazine said, is the common term used by New York politicians to refer to White Anglo-Saxon Protestants.
It seems that Governor Harriman is a Wasp and one reason his man was not acceptable as a Senate nominee was that he is a Wasp, too. Under the “balanced ticket” theory, one Wasp is enough in New York which has a superabundance of “anti-discrimination” laws applying to just about everything except politics.