The parasite turns the host into a bodyguard

There are many examples of parasites that bring about strange behavior changes for their hosts. For example, trematodes can cause ants, intermediate hosts, to move onto grass leaves in the evening and early morning. There, they used the upper jaw to cling to grass leaves, so they were eaten by sheep and the last host of trematodes. Conversely, non-parasitic ants return to the cave in the evening or cool times of the day.

Or another example is a land worm that kills a parasitic hairworm by jumping into the water, which is where adult worms reproduce. Such behavioral changes are believed to be caused by parasites to increase their infection to their hosts. But there are still other explanations. It is very likely that the host behaved differently before being parasitic. So being infected is a consequence of different behavior, not cause .

But there are still questions about the possibility of increasing infection: changing host behavior can make other animals more likely to attack, while this may reduce the likelihood of serious infection. important. Therefore increasing infection should be checked under natural conditions.

In a recent online article published in the journal Open PLoS ONE, the research team at the University of Amsterdam, the Netherlands, and the federal university of Vicosa, Brazil, directed by Arne Janssen gave evidence that change host behavior is beneficial for parasites in practice. In a study funded by WOTRO conducted in Brazil, they studied caterpillars eating local guava leaves and exotic eucalyptus trees. Small caterpillars are attacked by a parasitic insect, which quickly lays 80 eggs inside the caterpillar.

Caterpillar.(Photo: wikimedia.org)

Inside the host body (a caterpillar), a cruel play occurs: the eggs of the parasite, and the larvae hatch into the liquid part of the host's body. Caterpillars continue to eat, move and grow like their other non-parasitic sisters. When parasitic larvae are large, they escape through the host's skin, and begin to grow nearby. Unlike the combination of host and other parasites, caterpillars continue to live but change strange behavior: it stops eating and lives close to the parasite of the parasite. Furthermore, it protects the parasite's pupae from other predators by shaking its head violently.

Caterpillars die after the adult parasite comes out of the pupae, so there are no benefits for caterpillars. In contrast, non-parasitic caterpillars do not have these behavioral changes, but continue to eat and mature. The team found that in fact, larvae of the parasite-protected parasite had a half-time attack of predators compared to unprotected ones. Therefore, behavior changes in hosts increase the survival of parasites because hosts act as a bodyguard for the pupae of parasites.

How the parasite can change host behavior is not well understood, but this is an interesting research topic. The team found that one or two parasitic larvae remained within the host. Maybe they have influenced the behavior of caterpillars, they must sacrifice themselves for their siblings.

Quote: Grosman AH, Janssen A, de Brito EF, Cordeiro EG, Colares F, et al. (2008) Parasitoid Increases Survival of Its Pupae by Inducing Hosts to Fight Predators. PLoS ONE 3 (6): e2276. doi: 10.1371 / journal.pone.0002276 - http://www.plosone.org/doi/pone.0002276