How to check lentils for bugs
There are liable to be insects among the lentils (as with other small legumes and with rice). In addition, lentils may be infested internally, like large legumes (such as dried beans and chickpeas). This holds true both for split and whole brown lentils. In some countries (such as Canada and Australia), where the lentils are grown under conditions of advanced technology, the internal infestation is not common. In other countries (like Turkey) where primitive methods of growing and storage are used, internal infestation is found. Inasmuch as it is hard to discern internal infestation, and it is difficult for the private consumer to determine where the product was produced, it is recommended that only lentils with a superior kashrus supervision, which oversees the quality of the lentils, be used.
from R Moshe Vaye, see: https://dinonline.org/Bedikat/lentils