Try putting a clear bag over it at night with a lamp on . Usually the light will attract the insects. Holes in the leaf are signs of a slug or other insect eating the leafs. Clean off the remnants left behind with a Q-Tip dipped in alcohol.
Or use a granular systemic to sprinkle on the top soil. Each time the plant is watered it Will retain and absorb the systemic to eliminate soil insects or flying insects that feed on the plant.
