Giant panda Shuan Shuan's charms failed this time. The 16-year-old, in Japan on a breeding mission from Mexico, was unable to spark the interest of Japan's male panda Ling Ling, and breeders have resorted to artificial insemination, Tokyo's Ueno Zoo said Tuesday.

Shuan Shuan had come into heat and the two had exchanged glances across a fence, but "Ling Ling showed no signs of feeling compelled to mate naturally," the zoo said in a statement.

"Sperm was extracted from Ling Ling and artificial insemination was performed" on Monday, it said.

The zoo expects to find out in July if the operation was successful.

Ling Ling, 18, had made three previous trips to Mexico City's Chapultepec Zoo, but attempts there had ended unsuccessfully after he showed signs of being ill at ease.

The first took place from January to April 2001, while the second took place from November 2001 to April 2002. Ling Ling's third impregnation attempt at Chapultepec Zoo lasted three months, beginning in January 2003.

Zoo officials had decided to bring a female to Tokyo, hoping Ling Ling would feel more comfortable on his own turf.

If Shuan Shuan is successfully impregnated, she will remain in Japan until spring 2006 to watch over her offspring.

If she does not get pregnant, she will return to Mexico in August.

Despite attempts to save the endangered species, breeding pandas in captivity has proved difficult.