The Tomato Hornworm

A Parasitic Host


Parasitism Defined The Tomato Hornworm
We have all heard of parasites. Humans are occasionally infected with parasites such as tapeworms, round worms, mosquitoes and leeches. Parasitism is a biological relationship in which one species benefits; while harming the other and can occur in the smallest biolgoical niche. Because the parasite needs the host to remain alive, it is typically advantageous for the parasite NOT to kill its host, however there are examples of when death of the host occurs. An example of this is seen in the photo below. In the photo, a tomato hornworm is covered with cocoons of pupating braconid wasps. The braconid wasp is considered a parasitoid of the hornworm because it causes the hornworm to die as it pupates. By the time the wasps undergo metamorphosis, all of the hosts insides have been digested, thus by the time they are ready to pupate, the caterpillar will die. While this may be detrimental to the tomato hornworm, it is considered beneficial for gardeners...as the tomato hornworm can be a signifant pest. Parasitism usually connotes a negative feeling; however as seen in this case, it can be considered beneficial.