NOT since the Mormon Tabernacle Choir was formed in 1847 has America been listening to so many singing Mormons. They are calling them the Mormon melody mafia - an improbable group of singers, dancers and wannabe entertainers who have been taking US reality TV shows by storm.

When more than 20m viewers phoned in their votes to the penultimate episode of American Idol last week, they chose David Archuleta, a clean-cut Mormon teenager from Utah, as one of the two finalists for the country’s most popular talent contest.

A couple of weeks earlier, Brooke White, a blonde Mormon housewife from Arizona who revealed that she had never watched an X-rated film, was eliminated after joining Archuleta in the top five.

The Idol advances followed a remarkable pattern of Mormon successes in a wide range of television contests, from Dancing with the Stars, a celebrity ballroom dancing competition - won twice by Julianne Hough of Utah - to a series of Survivor set in China and won by Todd Herzog, who has become known as “the gay Mormon”.

With Mormons also starring in numerous other shows - including a Food Network cooking contest featuring Kelsey Nixon, who declared herself to be “a sweet little Mormon girl from Utah” - America has begun to wonder how a marginal religious community has managed to make a televisual impact out of all proportion to its size.

“With 5.5m church members in the US, they represent less than 2% of the population,” noted Mo Rocca, a popular satirist and television critic. “And yet they are 40% of the Idol top five. Are they simply better at singing than other Christian denominations?”

The Mormon success seems all the more striking because the sect continues to be regarded with considerable suspicion by many Americans, as Mitt Rom-ney, the former Republican presidential candidate, discovered to his cost when his Mormon beliefs became an issue early in the primary campaign.

Yet other critics have noted that the wholesome lifestyle and innocent demeanour of many young Mormons are ideally suited to mainstream American television, which still eschews nudity and swear words.

Mormons who are prepared to shed their goody-goody image have also proved popular on reality shows – notably the Mormon contestant who was known as “the Idaho virgin” but ended up sucking the toes of an eligible bachelor on a cable-channel dating show.

The emergence of Archuleta, 17, as a favourite to win Idol has ignited debate about the possible keys to Mormon success.

With his big-ballad voice, “aw, shucks” smile and self-effacing modesty, Archuleta was a favourite from the start with grandmothers and preteen girls, both important Idol viewing constituencies.

Simon Cowell, the British judge on American Idol, described him last week as “a chihuahua trying to be a tiger”, but the word used by most critics to describe both Archuleta and White was “safe”.

Others have argued that Mormon family traditions of singing and dancing - stretching back to campfire nights on the great 19th-century Mormon trek to Salt Lake City - give amateur contestants a head start when performing in public. The community is close-knit and well organised and forms an energetic voting bloc. Reality show producers have often noted a surge in telephone voting after their shows air in Utah.

Many Mormon families preserve a tradition of Monday night “family home evenings”, which critics believe may have helped the reality show career of a member of the other great Mormon singing institution - the Osmond family.

Marie Osmond competed last year in Dancing with the Stars. She advanced to the top three and may have been helped by the show’s being aired on Mondays, when Mormon viewer-voters tend to be at home.

The Mormon church, known to itself as the Church of Jesus Christ of Latterday Saints, has been generally supportive of reality show contestants, although Julie Stoffer, an unmarried student at the Mormon-run Brigham Young University, was suspended for living with male housemates in a Big Brother-style show.

Success can also be more complicated for Mormons. If Archuleta wins American Idol this week he will have to decide whether to pursue a professional singing career or to put it on hold for two years once he turns 19, the age at which Mormons are expected to undertake two-year evangelical missions before beginning university studies.

Archuleta’s bishop has suggested that entertaining millions as a clean-cut ambassador for the church might be considered such a mission.

The teenager’s rival in the Idol final has no such concerns. David Cook, from Missouri, is an unshaven rock’n’roller who used to be a barman. For some of Archuleta’s supporters, it’s a clear choice between good and evil.

Video: David Archuleta sings "With You" [Chris Brown] on American Idol

Video: Dancing with the stars: Apolo Anton Ohno and Julianne Hough dance the paso doble

Video: Julianne Hough wins Dancing with the stars

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