An Insecticide is a chemical that is used to kill insects that are living on your plants and will also prevent any from coming to eat them, these insects can include anything from insect eggs to large bugs.
An obvious signifier of an insect infestation or problem on your plants is that you’ll be able to see them there if you look closely. However, some can live in the soil and be affecting the health of your plant through the roots. Some other signs to look out for are a sudden change in leaf color or texture, or if your leaves are becoming misshapen or shriveled.