While checking my tomato plants the other night I noticed that the dreaded hornworms were feasting away on my beautiful tomato and pepper plants. As I started looking for them, I remembered a conversation that my husband and I had last fall. He had seen a post on the internet about using a black light flashlight in the garden at night to look for hornworms. I was skeptical but thought that I would give it a try.
Much to my surprise it worked great! Hornworms are among several different insects that have bioluminescent properties which allow them to glow or light up when they are exposed to a black light. I looked over a period of 3 nights and found several each time ranging from very small to very large.
During the hunt I found three that were being parasitized by the tiny braconid wasp Cotesia congregate. The wasp lays its eggs inside of the horn worm and those eggs hatch into larvae. Those tiny larvae feed on the inside of the hornworm until they are ready to pupate and then they emerge from the hornworm and spin a cocoon around them. They complete their life cycle inside of the cocoon, emerge from the cocoon and start to feed on more hornworms. If you see hornworms with little white sacks all over them, leave them in the garden because they are beneficial.
If you see damage on your tomatoes but can't find the hornworms grab your black light flashlight and head to the garden!
If you would like to see the lifecycle of the braconid wasp check out this cool video from Purdue University https://www.youtube.com/watch?v=nZZyJQNmOV8