Photo: Wikipedia Commons
Ah, the tomato. A much beloved fruit, although many enthusiasts of Lycopersicon esculentus might give it a second thought if they knew that it is spawn of the nightshade family (Solanaceae), which contains many very poisonous species. But there's obviously no issues with eating the ripe plump succulent fruit, or our world's population would not be what it is. You'll not want to graze on the foliage, however, as it contains small amounts of various toxins, true to the tomato's nightshade heritage.
One of my co-workers mentioned that she had plenty of tobacco hornworms noshing on her tomato crop, and that many were victimized by a very interesting and oft-seen hornworm predator. I convinced her to cup one up and bring it into the office so I could capture some images, and she most kindly did just that.
NOMENCLATURE NOTE: Sometimes caterpillar common names are confusing, and this is one of those cases. Manduca sexta is an example of a moth that has different names for the adult (Carolina sphinx) and the larva (tobacco hornworm). In this case, it is doubly confusing as there is also a tomato hornworm, Manduca quinquemaculata, larva of the five-spotted hawk moth. It is also a nightshade specialist, but is far less commonly found on tomatoes than is the tobacco hornworm. The common names of these two species should probably switched for clarity's sake.
Photo: Beatriz Moisset/Wikipedia Commons
The wasps are tiny indeed, as can be seen in this image. Note how neatly the tips of the cocoons rupture when the adult wasp pushes its way out. Female Cotesia wasps seek out tobacco hornworms, and when a victim is located, she'll inject numerous eggs into its tissue with a needlelike ovipositor. Along with the eggs comes symbiotic viruses that hamper the caterpillar's defense systems. The wasp eggs hatch in about two days, and the little grublets begin devouring the nonvital soft parts of the caterpillar's innards.
Nature is chock full of predators on every level, and the hornworm/Cotesia wasp dynamic is an especially obvious example of a predator-prey relationship that would normally go unnoticed. I recently wrote about two similar but far less seen parasitoids HERE. Were it not for the legions of predators engaging and killing their legions of victims, ecosystems would go wacky. Even though some of the tactics employed by insect predators - especially, perhaps, the parasitoids - seem grisly, they are also fascinating studies.
In this case, we have a plant - the tomato - that has evolved chemical toxicity that is effective enough to exclude most caterpillars from eating its foliage. Some tubular warriors will always manage to battle through the plant's chemical defense systems, and in this case the hornworm is the conqueror. It wins two prizes, as not only does the caterpillar get to nosh on tomato foliage free of competing herbivores, it also sequesters the nightshade's toxins and thus becomes unpalatable to most predators. Nothing is enemy-free, however - enter the parasitoid Cotesia congregata wasp. But the wasp undoubtedly has its enemies as well. It may well be victimized by even more devious hyperparasitoids - other wasps whose larvae consume those of the parasitoid. Even if that doesn't happen, the adult wasps are vulnerable to scores of predatory insects, songbirds, and others.