Q. If someone removed an insect from the lettuce leafs of a salad when rinsing it in water on Shabbos, can one eat that salad that day?
A. Biur Halacha (319: 1 – haborer) quotes P’ri Megadim that after the fact when someone transgressed over the prohibition of borer, selecting or choosing items on Shabbos, one should not benefit on that Shabbos from the prohibited work done. However, he adds that following the opinion of Hagra it would be permitted when done unintentionally. This is different from bishul or cooking, where there is a change done on the food itself.
Ketzos Hashulchan 125, Oz Nidberu 3:11, Piskei Teshuvos 119: 13 and others also rule leniently.
Rabbi A. Bartfeld as advised by Rabbonim at the Toronto Kollel