Unit 11 in Entomology [1] Unit 11: Insect Parasitism [2] In this unit, we’ll differentiate between the three types of symbiosis, describe the different ways to classify parasites, discuss the costs and benefits of endo versus ecto parasitism, differentiate between parasite and parasitoid, define hyper, multiple and gregarious parasitoids, and explain in insect terms why being small is actually good. We’ll discuss more about parasites, but for the time being, take a look at the photographs below. Both of these are lice that can be found on chickens. One is found on the body and one is found on the feathers. Take a look at the morphological differences. Why do you think they’re shaped so differently? These are some things to think about as we discuss insect parasitism. [3] In this unit, we’ll discuss insects that parasitize humans, mammals, and other arthropods. You will first learn the difference in three symbiotic relationships, and between parasite/parasitoid, parasitoid/predator, and about various endo and ecto parasites. Prepare yourself for some repugnant pictures that illustrate some damage that insect parasites can do to other animals. [4] Symbiotic relationships refer to interactions between two different species. In fact, when broken into its Greek roots, the word symbiotic means “life together”. Sym means together and bio means life. In this unit you’ll first learn about three different types of symbiotic relationships: mutualism, commensalism, and parasitism. The balance of the unit will then focus on various aspects of parasitism. These terms are generally used to describe the relationship between species, but can also be used for interactions within a species, particularly humans. Mutualistic relationships are those in which both species involved benefit. For example, most friendships are a mutualistic relationship. As you can see in this picture, ants and aphids have a special mutualistic relationship. The aphids feed the ants by secreting a sugary solution called honeydew through cornicles on the tip of their abdomen. These ants, in return, protect the aphid by attacking predators such as ladybugs. [5] The second type of relationship is commensalism. In commensal relationships, one species benefits but the other neither profits nor is harmed. In this picture, orchids are growing on the side of a tree. The orchid needs the tree for support and protection, but the tree doesn’t benefit, not is it harmed, by the orchid’s presence. Relationships in which one species benefits at the expense of the other is a parasitic relationship. A good example of this is a mosquito and a human relationship. As pictured here, this mosquito has inserted her mouth part into a human to draw out a blood meal. The human will have a nice itchy lump where the mosquito has injected its poison, but the mosquito will use the protein it got from the blood to make her eggs. [6] Insects, more than any other arthropod class, practice parasitism. We humans are mostly aware of the insect parasites that affect us. Mosquitoes seem to be everywhere we go. Your household pets are commonly affected by fleas and schools often have to check for outbreaks of lice among the students. Not only do insects harm us, but they also harm other mammals, vertebrates, invertebrates, and even members within their own class, as depicted in the table below. Some orders are 100% parasitic. Some of these include Mallophaga and Anoplura and Siphonaptera. Hymenoptera are the next highest, with 50% of its members being parasitic. You’ll learn about a few wasps that use other insects as their host later in the unit. [7] There are two types of parasites we will be discussing in this unit: endoparasites and ectoparasites. Endoparasites are parasites that live within the body of its host, and an ectoparasite lives outside the body of its host. What type of parasite would a mosquito be, endo or ecto? It would be an ectoparasite, because it lives off of our blood by sucking it from the outside of the body. [8] Here are a few insect examples of endo and ectoparasites. First, endoparasites. An example is the tree squirrel bot fly. Bot flies often lay their eggs on habitat substrates where mammals live. When these eggs hatch into larvae, the larvae enter a body orifice, such as eyes, mouth, nose, anus, or a wound. They migrate for about a week through the host’s body before choosing a site to settle underneath the skin. There they cut a warble pore through the host’s skin from the inside out. Rodent and rabbit-bot flies rarely infect humans, but when they do, they may bore directly through a person’s skin from outside in. At pupation time, the larvae crawl out of their mammalian host and drop to the ground to pupate. And for those of you who are curious, or totally want to be grossed out, there is a human bot fly. To view more photos of the squirrel bot fly, please visit the bot fly website at botfly.ifas.ufl.edu. [9] Now let’s take a look at another bot fly, the horse bot fly. The horse boy fly, in the genus Gastrophilus, has a slightly different life cycle than that of the squirrel bot fly. Adults bot flies deposit the eggs on the forelimbs and head regions of a horse. As the horse licks its coat, it stimulates the eggs to hatch. The larvae then burrow into the mucosal membranes of the horse’s lips and gums and migrate to the stomach area. Here the larvae feed and may cause ulcers which can be fatal to the horse. Eventually, the horse will pass the larvae through fecal matter. Once on the ground, they pupate for about 1-2 months, before emerging as adult flies, which will then lay its eggs on the horse’s hair or skin for another generation of bot flies to hatch. Remember how I said in the life cycle of a horse bot fly, the larvae migrates from the mouth to the stomach area? If you take a look at the photo below, you’ll see the maggots in the stomach that killed a horse. [10] Now let’s take a look at some ectoparasite examples. Bedbugs: “Don’t let the bedbugs bite!” Did your parents ever say this to you when tucking you in at night? Bedbugs are an insect that feed on the blood of vertebrates, particularly humans. They like to feed at night and will crawl out of the seams of mattresses or from cracks and crevices where they stay during the daylight hours. When they bite, bedbugs have a welt similar to a flea or mosquito bite. Some people have a more severe reaction than others. Some people may have no reaction at all. Bedbugs are again becoming a problem in the United States. Pest control companies are recording large numbers of calls about bedbugs in homes from people who have recently stayed in a hotel or gone on a cruise. Bedbugs have a sweet odor and leave behind blood spots when they feed. If you suspect bedbugs in a place, pull back the bedding and check the seams of the mattress and box springs for small brownish spots. Bedbugs live in cracks and crevices during the day, so can be hard to spot. They are also very quick moving, so it can be hard to catch once you see one. To view a bedbug feeding, take a minute and watch the bedbug video. A bedbug colony was discovered in a student’s apartment near the University of Florida’s campus. The apartment tenant had purchased a used mattress and had a few unwanted inhabitants. See the piercing-sucking mouthparts as they probe for a blood vessel. Watch how the bedbug takes its blood meal, and then defecates out excess water at the conclusion of the meal. [11] (Bedbugs Feeding video) [12] Another example of an ectoparasite is a flea, and these guys like to feed on mammals and some birds. They are flattened side to side, which helps them navigate in between the host’s hairs. Flea larvae do not live on the host, but on the ground, bedding, or on other furniture. After pupating, the emerged adult flea jumps onto a host to feed on its blood. Some people are very allergic to flea bites and others may not react at all. [13] Remember we said in the chart before 50% of Hymenopterans are parasitic? Well, some wasps are able to find and parasitize beetle larvae that live in the soil. The picture on the left shows a wasp larva feeding on the side of a beetle grub. Remember, the beetle grub is the larger of the two in the left hand picture. On the right hand side, it shows the same wasp larva after it has consumed the beetle and, in the process, has grown much larger. [14] Many parasites do not kill their hosts. Fleas may weaken the host by sucking too much blood, but this action does not kill the animal they’re living on. However, there is a type of parasite that kills its host. It’s called a parasitoid. Only the larvae of holometabolous insects are parasitoids, especially in the Diptera and Hymenoptera orders. Because they kill their hosts, parasitoids are often used to kill insect agricultural pests like aphids, cabbageworms and European corn borers. Parasitoids have also been used to control house and stable flies. Some parasitoid examples include the tarnished plant bug parasitoid. This wasp, from the family Braconidae, is laying an egg on a tarnished plant bug.