Leaf eating pests on my Guava tree :( | Plant Pests | Commercial Hydroponics farming

Hi,

I have a 3 - 4 year old medium sized guava tree in my garden that has just started flowering. However, I have been observing that some insects are eating away its leaves. I haven't been able to identify the insects but there aren't any eggs on the backside of the leaves. The picture of the eaten leaves is attached. I tried using Methyl Parathion but am not sure if it is working. What should I do?