South Bay

Exterminators sprayed bait containing the pesticide malathion on 31 properties in San Ysidro and National City this week after five adult Mexican fruit flies--including an egg-bearing female--were found in orange trees there last week, County Agricultural Commissioner Kathleen Thuner said.

However, the discovery of the flies, three of which were fertile females, may prompt more extensive action by the Department of Food and Agriculture’s Science Advisory Panel, which meets Friday in San Ysidro.

The panel may choose to release as many as 6 million sterile fruit flies to help prevent an infestation, Thuner said.

She said the U.S. Department of Agriculture, in conjunction with its Mexican counterpart, has been releasing sterile fruit flies south of the border to help prevent the spread of the flies, which spoil fruit by burrowing inside it to lay their eggs.

A successful eradication program requires a 100-1 ratio of sterile to fertile flies, which must be maintained for at least two generations, Thuner said. The last major infestation of Mexican fruit flies in the San Diego area occurred in 1954 in San Ysidro, she said.