As I got tired of picking up caterpillars one by one, so I invented another way. The new way was to use the dish soap. I have heard that insects breathe via little holes scattered on their skin instead of mouses. So if they were covered by something like gel, they will die due to lack of oxygen. Whenever I found a caterpillar, I poured did dish soap on them. finally, I just sprayed the dish soap to overall of the green. It works well.I didn't have to pick them up one by one but I could get rid of all the insects with one action. However it made another issue.