Where there are tomato plants there are often hornworms and where there are hornworms you are likely to find braconid wasps. Like many pests, hornworm caterpillars enjoy the newest greenest leaves and youngest fruit. They spend their morning and afternoons munching away before retreating to the base of the plant to rest in the evening.
During the summer months, we spend much of our early morning hand picking individual hornworms off their host plant. It is important to remove as many of them as possible to ensure they are unable finish out their life cycle and return the following season. This task is not only tedious and undesirable, it is one of our only weapons against this pest during the high season. However, come autumn evidence of the braconid wasps work is showing itself and will soon do away with any hornworms that may have been left behind on the tomato plants.
Braconid wasp although terrifying and savage to some are an incredible ally for organic farmers in the battle against hornworms. Braconid is a parasitic wasp that uses a remarkable weapon to disable the defenses of their host insects - a virus. The braconid wasp's life cycle begins when a female braconid deposits her eggs and injects the virus inside the hornworms body. Once the virus is injected it immediately goes to work disabling the host's defenses against intruders. Without the virus running interference, the host insect's immune response would quickly destroy the wasp eggs. After the eggs are laid the larvae develop and feed inside the caterpillar. When they're ready to pupate, the braconid wasp larvae chew their way out of their host, and spin silk cocoons on the caterpillar's exoskeleton (pictured below). The tiny adult wasps emerge from these cocoons a short time later. The affected caterpillar may continue to live as the braconid wasps are developing inside its body, but it will die before it can pupate. After emerging the adult braconid searches for a mate and the cycle begins again.
Witnessing the full life cycle of the braconid wasp is one of those things that is both fascinating and brutal. The inter-workings of how all species, ourselves included, are connected is just one of the things we are working to understand and utilize in our farming practices. Each season we learn more and more about how to better work with our ecosystem and the payoff has been two fold.