Assuming that vegetables are insect-free

Hi,

If a majority of members of a given set have a certain positive halachic characteristic, but that is only due to an action performed upon the set, then one may not assume that this characterstic will persist in the majority infinitely, and one must continue to check the members of the set for it.

Therefore: If growers of a particular type of vegetable employ tactics which eliminate non-kosher infestation, one may not assume that any particular vegetable in the sample is bug-free. One still must check the vegetables, although the check need not be as rigorous as in cases where that particular tactic is not employed.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:91:3)

Have a great day,
Mordechai