However, when we have an infestation of 'bad' caterpillars devouring our basil before we have a chance to, it's time to dispose of them on that particular plant. The best and safest means of doing so is by using a naturally-occurring soil bacteria called Bacillus thuringiensis , or Bt, a very specific organic insecticide. It affects only leaf-eating cutworms, and does no harm to ladybugs and their larva, lacewings and their larvae, spiders, the wasps and hornets that devour caterpillars, or humans. You simply spray a liquid form of Bt on the leaves of a plant, and when the caterpillars come to dine the next time, they ingest the Bt which proliferates in their intestines and paralyzes their digestive systems. The caterpillars quickly starve to death.
Thrips are brown or tan, about one-eighth of an inch long.
They're very narrow, appearing the shape of a tiny alligator. They're hard to see with the naked eye, but their damage is very clear. Thrips chew the top surface of leaves, leaving a striped, tan dead layer of leaf behind. The damage can appear as 'white spots' on leaves, or a lacy or skeletal appearance on the leaves. Insecticidal Soap will kill thrips very effectively.