What is the definition of a bug that is forbidden to eat. Let’s say the one can see a litte dot with the visible eye, but then if one were to take a microscope one could see that the little dot is really a bug–is that considered seeing with the visible eye?
If the naked eye cannot discern the spot to be a bug, and it cannot be seen to be in motion, it is permitted to eat it.
Sources: Rabbi Shlomo Zalman Auerbach (Halichos Shlomo, chap. 4, p. 53, note 78) writes that a spot on an esrog, which to the naked eye is nothing more than a spot, but under the microscope is seen to be a chazazis, does not disqualify or reduce the quality of the esrog. He extends this principle to all areas of Torah law, which depend on human senses, for “the Torah was not given to Divine angels.” A similar principle is stated in Iggros Moshe (Yoreh De’ah, vol. 2, no. 146), and this is also the ruling given by Shevet Halevi (vol. 7, no. 122), who explicitly addresses the question of a black spot that looks innocuous to the naked eye, but is seen to be a bug under the microscope, and writes that if most people see nothing more than a black spot (with the naked eye), it follows that there is no prohibition. See also Shemiras Shabbos Kehilchasah, chap. 3, note 105, whose ruling is less clear cut on this point.