Word of the Day: Parasitoid (Biology)

Sunday, May 17th, 2009 | Science, Word of the Day |

Slashdot - Texas Makes Zombie Fire Ants:

What do you do when a foreign species has been introduced to your land from another continent? Bring over the natural predator from the other continent. Scientists in Texas have introduced four kinds of phorid flies from South America to fight fire ants. These USDA approved flies dive bomb ants and lay an egg inside the ant. The maggot hatches and eats away juicy tender delicious ant brain until the ant is nothing more than a zombie that wanders around for two weeks before the head falls off and the ant dies. A couple of these flies will cause the ants to modify their behavior and this will be a very slow acting solution to curb the $1 billion in damage these ants do to Texas cattle ranches and–oddly enough–electrical equipment like circuit breakers. You may remember zombifying parasites hitting insects like cockroaches.

“Zombifying” is a great word, but the scientific term for an insect pupa that eats its host is parasitoid:

A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism which it ultimately kills (and often consumes) in the process. Thus they are similar to typical parasites except in the certain fate of the host. In a typical parasitic relationship, the parasite and host live side by side without lethal damage to the host. Typically, the parasite takes enough nutrients to thrive without preventing the host from reproducing. In a parasitoid relationship, the host is killed, normally before it can produce offspring. When treated as a form of parasitism, the term necrotroph is sometimes (though rarely) used.

This type of relationship seems to occur only in organisms that have fast reproduction rates, such as insects or (rarely) mites. Parasitoids are also often closely coevolved with their hosts. Most biologists use the term parasitoid to refer only to insects with this type of life history, but some argue the term should be used more embrasively to include parasitic nematodes, seed weevils, and certain bacteria and viruses (e.g., bacteriophages), all of which obligately destroy their host.

Most of the common parasitoids I’m familiar with are wasps that prey on other insects or spiders: tarantula hawks, cicada killers, and dirt daubers. The first two bury the paralyzed host underground. The last carries away its much smaller spider victims and entombs them inside mud tubes the female dirt dauber creates by mixing earth and water in her mouth.

Interestingly, the Wikipedia article says that 10% of insects are parasitoid. I’ve have never guessed it was that many.

Aren’t you glad I spent six and half years getting a biology degree so I can explain this stuff?

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