Hollywood surveys the latest box office takings a new plot-line is emerging: the death of the movie star.

WE still envy their lifestyles, covet their Malibu mansions and marvel at their romances.

But as Hollywood surveys the latest box office takings a new plot-line is emerging: the death of the movie star.

Last weekend two titans of Tinseltown, Tom Hanks and Julia Roberts, appeared in Larry Crowne, a tale of middle-aged romance set amid economic recession. What was meant to be an uplifting rom-com left studio bosses weeping into their Martinis.

The ingredients were in place for a hit: a release over the Fourth of July holiday weekend; two A-list actors, each with a back-catalogue of blockbusters. But the reviews were tepid; the public unenthused.

Having cost dollars $27 million to make, the movie is deep in the red.

One turkey may not make a trend, but Larry Crowne joins a lengthening list of failed star vehicles. Tom Cruise and Cameron Diaz could not lure audiences to the spy romp Knight and Day. Johnny Depp, Hollywood's best-paid actor, and Angelina Jolie did not save The Tourist from commercial failure. Ryan Reynolds failed to set Green Lantern alight and How Do You Know?, which starred Reese Witherspoon, Owen Wilson and Jack Nicholson and cost dollars $75m to make, barely registered.

Instead, this has been the summer of blockbusters sans superstars: Super 8, Fast Five, Bridesmaids, The Hangover Part II and Transformers 3.

''Something profound is happening," said Peter Bart, the former Variety editor. "Where are today's equivalent of the idiosyncratic superstars of the past? The Spencer Tracys, Katharine Hepburns, Humphrey Bogarts - the stars who could carry a film?"

Exceptions prove the rule: Black Swan cost just dollars $12m to make and grossed more than dollars $306m last year, largely because of an Oscar-winning performance from Natalie Portman. Elsewhere, however, mounting evidence points to the demise of the film star.

The producers of Transformers 3, the biggest hit of the year so far, dropped their original leading woman, Megan Fox, to replace her with the unknown Rosie Huntington-Whiteley. It mattered not a jot, probably because the real stars of the movie are its special effects.

Last week witnessed the release of the final part of the Harry Potter series, a franchise that has grossed more than dollars $5.6 billion so far and which plucked its main stars from obscurity. The highest-grossing movie yet, unadjusted for inflation, was the 3D epic Avatar.

It starred Sam Worthington, an actor most notable for his anonymity.

Numerous theories seek to explain the demise of the Hollywood icon.

Some posit that America is now too unsure of itself to launch new lone-wolf heroes in the vein of John McClane or Rambo.

Others suggest that the biggest stars became too huge, causing the economic structure of Hollywood to implode.

The example most often cited is that of Tom Cruise, who earned dollars $70m for Mission: Impossible II and was dropped by Paramount shortly afterwards. Cruise is often said to be the shrewdest actor in Hollywood.

Tellingly, his next project is an ensemble piece based on a Broadway show, Rock of Ages. Other pundits suggest that the credit-crunched studios are exercising prudence by signing several lesser-known actors for individual projects, rather than banking on one big name. Or that filmmakers are following cues from hit television series, such as Mad Men and The Sopranos, which have large, sprawling casts.

But the most compelling argument is rooted in Hollywood's increasing reliance on overseas audiences.

Big special effects cross language barriers better than nuanced performances, noted Mr Bart, who helped to make The Godfather while working at Paramount Pictures. The wit of a Cary Grant, the menace of a Robert De Niro, the gravity of a Marlon Brando - all are rather harder to translate into Russian, Mandarin or Hindi than the spectacle of one giant robot pummelling another.

"When Paramount was deciding to make The Godfather, the question of how it was going to do overseas wasn't a factor," Mr Bart recalled.

"Times have changed. The studios no longer know how to nurture what was once their most valuable resource. All the effort is being channelled into building new franchises from comic-book heroes."