Main Difference – Parasites vs Parasitoids
Parasites and parasitoids are two type of organisms that benefit at the expense of the host. Endoparasites and ectoparasites are the two main types of parasites categorized based on the type of habitat. Endoparasites live on the host while ectoparasites live inside the host. The main difference between parasites and parasitoids is that parasites do not kill their host whereas parasitoids always kill their hosts. The young of the parasitoid develop on or within the host. Since they kill their host, parasitoids are considered to have predatory characteristics as well. Mosquito, leech, mite, flea, tick, louse worms such as roundworms, tapeworms, and trematodes and protozoans such as Plasmodium and Amoeba are parasites. Wasps, beetles, flies such as tachinid flies and worms such as Gordian worms are parasitoids.
Key Areas Covered
1. What are Parasites
– Definition, Features, Types
2. What are Parasitoids
– Definition, Features, Examples
3. What are the Similarities Between Parasites and Parasitoids
– Outline of Common Features
4. What is the Difference Between Parasites and Parasitoids
– Comparison of Key Differences
Key Terms: Ectoparasite, Endoparasite, Host, Parasites, Parasitoids, Predators
What are Parasites
Parasites refer to the organisms who live in or on another organisms and benefit by deriving nutrients at the expense of the host. As parasites grow, feed, and seek shelter from the host organism, the relationship is harmful to the host organism. Though most parasites do not kill the host organism, some parasites may eventually kill the host. These parasites are pathogenic, causing diseases in the host. Typically, parasites are small in size than the host organism. But, they exhibit higher reproduction rates once they invade the host. Animals, plants, fungi, bacteria or virus can act as parasites. A parasitic fungus that is parasitic on plants is shown in figure 1. This fungus is a saprophyte that feeds upon the plant it kills.
Figure 1: Armillaria mellea (honey fungus)
Parasitic plants derive their nutrient supplements from another plant. About 1% of angiosperms are parasitic. They possess modified roots called haustoria that penetrate the host plant to connect with the conductive system, either xylem or phloem. Thus, they can extract either water, nutrients or both from the host plant. A parasitic plant is shown in figure 2.
Figure 2: Cuscuta
Arachnids, insects, and crustaceans-like ectoparasites and roundworms, flatworms, and protozoans-like endoparasites are some examples of animal parasites. Parasitoids and epiparasites are other two types of parasites. Endoparasites can be either intercellular parasites or intracellular parasites. Intercellular parasites live outside of the cell such as inside blood vessels or intestine. Intracellular parasites can be single-celled protozoans, bacteria, and viruses that live inside the cells. Epiparasites feed on another parasite. Animal parasites can either be parasitic on animals or plants.
What are Parasitoids
Parasitoids refer to the organisms who live as parasites and eventually kill their host. The immature stage of the parasitoid lives in or on the host. The development of the parasitoid may eventually kill the host. The lifecycle begins when the adult female lays eggs on the body of the host. After hatching, the larva feeds on the insect. Since the growth of the parasitoid eventually kills the host, parasitoids are considered as a type of predators. A parasitoidal wasp, ovipositing into the body of an aphid is shown in figure 3.
Figure 3: A Parasitoidal Wasp, Ovipositing into the Body of an Aphid
Wasps, beetles, a few flies, and twisted wing insects are some examples of parasitoids. Some wasps such as mud daubers paralyze insects to seal them with an egg in a nest so that the emerging larva can feed upon the victim. Weevil, spider, and long-horned grasshoppers are the hosts of the wasps. The tachinid flies lay eggs on the bodies of insects such as true bugs or caterpillars. On that account, parasitoid wasps can be used as a biological control as they kill the harmful insects to the crop. A parasitoid plant that grows on a rainforest tree is shown in figure 4.
Figure 4: A Parasitoid Plant
Parasitoid plants exploit host’s resources such as light and space as well as support from the host.
Similarities Between Parasites and Parasitoids
- Both parasites and parasitoids benefit at the expense of a host.
- Both parasites and parasitoids can be either animals or plants.
- Both parasites and parasitoids can be either ectoparasites or endoparasites.
- Both parasites and parasitoids are smaller in size than their hosts.
- Most parasites and parasitoids are specific to their hosts.
- Both parasites and parasitoids function at low host density.
Difference Between Parasites and Parasitoids
Definition
Parasites: Parasites refer to the organisms that live in or on another organisms and benefit by deriving nutrients at the expense of the host.
Parasitoids: Parasitoids refer to the organisms that live as a parasite and eventually kill their host.
Killing the Host
Parasites: Generally, parasites do not kill their hosts.
Parasitoids: Parasitoids eventually kill their host.
Diurnal/Nocturnal
Parasites: Parasites can be either diurnal or nocturnal.
Parasitoids: Parasitoids are nocturnal.
Specificity
Parasites: Parasites can have several hosts during their lifecycle.
Parasitoids: Parasitoids are highly host-specific.
Significance
Parasites: Parasites live on or inside the body of the host.
Parasitoids: Parasitoids spend a significant portion of their lifecycle within the host.
Susceptibility for Biological Control
Parasites: Parasites are less susceptible for a biological control.
Parasitoids: Parasitoids are highly susceptible for a biological control.
Examples
Parasites: Mosquito, leech, mite, flea, tick, louse worms such as roundworms, tapeworms, and trematodes and protozoans such as Plasmodium and amoeba are parasites.
Parasitoids: Wasps, beetles, flies such as tachinid flies, and worms such as Gordian worms are parasitoids.
Conclusion
Parasites and parasitoids are two types of organisms that benefit at the expense of the host. Parasites live on or inside the host. Typically, they do not kill their host. Parasitoids are a group of parasites that spends its immature stage of the life on or inside the host. Parasitoids eventually kill the host. The main difference between parasites and parasitoids is the effect of the parasitism on the host.
Reference:
1. Nordqvist, Christian. “What is a Parasite? What do Parasites do?” Medical News Today, MediLexicon International, 26 Feb. 2016, Available here.
2. “Parasitism.” Wikipedia, Wikimedia Foundation, 16 Dec. 2017, Available here.
3.”Parasitoids”,bugs.bio. Available here.
4. “Parasitoid.” Wikipedia, Wikimedia Foundation, 12 Dec. 2017, Available here.
Image Courtesy:
1. “Armillaria mellea, Honey Fungus, UK 1” By Stu’s Images (CC BY-SA 3.0) via Commons Wikimedia
2. “Cuscuta parasite plant” By Khalid Mahmood – Own work (GFDL) via Commons Wikimedia
3. “CSIRO ScienceImage 2357 Spotted alfalfa aphid being attacked by parasitic wasp” By CSIRO (CC BY 3.0) via Commons Wikimedia
4. “Ficus watkinsiana on Syzygium hemilampra-Iluka” By Poyt448 Peter Woodard – Own work (Public Domain) via Commons Wikimedia
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