Bug-B-Gone is an item in Pocket Harvest used to repel those pesky bugs in your farms. Its recipe is unlocked when you finish the first specialty of a set number of buildings on your farm.
The recipe for Bug B Gone calls for two bottles of the vitamin component (light green) in order to be crafted.
The easiest way to unlock specialties in Pocket Harvest is to have a Bio Lab next to a cluster of vegetables and fruits that you can turn on and off.
For this set of farms, you'll want to maximize yield via cultivation. In addition, you'll want to increase the components you can extract by "Using Items" on that particular farm plot.
After collecting some components from the Bio Lab, go to Specialties from the Items menu, and upgrade the first level of as many facilities as you have.
Bug-B-Gone's recipe will be unlocked when you have specialities in a number of buildings on your farm.
To get rid of those pesky catepillars, you actually don't need Bug-B-Gone. You can zoom in and tap on the bug to get rid of it. However, sometimes you will have to try a few times to actually get rid of the bugs.