Setae vs pupal cases

Hello, I’m Amanda McNulty with Clemson Extension and Making it Grow. My son Conrad is obsessed with growing tomatoes in his tiny yard in Los Angeles -no fungal diseases and he has pretty good success. He called recently about giant caterpillars eating his tomato plants – the tomato horned worm. I told him that if the caterpillar got projections from its back that it was no longer a threat to his having BLTs for supper. These projections are not setae – the sometimes benign sometimes poisonous structures on some caterpillars. Rather, they are the pupal cases of Braconid wasps that have eaten the inside of the caterpillar, causing it to stop feeding. He moved the caterpillar from an heirloom plant to a tomato plant that he considered a grocery store type, he will make tomato sauce from those that survive.