A thick blanket of fog forced agricultural officials Wednesday night to postpone planned aerial pesticide spraying of a portion of the city's west side to try and eradicate an infestation of crop-destroying Mediterranean fruit flies.

Three helicopters fitted with sprayers were scheduled to lift off from Santa Monica Municipal Airport at 10 p.m. Wednesday, but fog forced them to postpone the spraying until Thursday evening, weather permitting, said Virginia Lopez, an entomologist for the California Department of Food and Agriculture.The spraying of the pesticide malathion over a 35-square-mile area was ordered earlier this week after 30 of the crop-destroying Medflies were discovered over the weekend.