Entomophagous parasites are insects that are parasitic on other insects; meaning that one organism attaches itself onto another organism, commonly known as the host, and collects nutrients for survival.  Parasites are defined as small organisms that complete most or all of their life cycle within a host, and many are capable of a high degree within host replication. Nearly all insects encounter other insect parasites within their lifetime. In general, arthropods that are considered parasitic are usually smaller in comparison to their host, they are only parasitic at the larval stage (unlike the pupal stages), each larva is limited to only one host and therefore results in the parasite to internally parasitize, and last but not least parasitic insects have a tendency to have a specific range of hosts. According to the Midwest Biological Control News, “(i)t is estimated that, on a world-wide basis, there are about sixty eight thousand species of parasitoids that are known to science and have been given a scientific name, (which) constitutes a little under ten percent of all known insect species.” One of the most commonly known and successful parasitic insect of these sixty eight thousand is the phorid fly.

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There are five parts to the process of parasitism for the phorid fly. First being that the parasite must locate where the host resides, then locate the host itself, pursue the host until accepted, distinguish between hosts that have already been attacked and hosts that have some potential to be parasitized, and finally establishing host regulation.  Besides developing an effective process, the phorid flies are considered successful parasites because of their parasite-host relationship with ants. Through this relationship, we can observe the process of natural selection, which is defined as, a process where organisms, which are adapting better to their environments or surroundings, tend to survive and produce more offspring. By “diminish(ing) the foraging activity of ants, frequently reducing the number and average size of foragers, and reducing the amount of food retrieved by a colony,” phorid flies not only obviously dominate in the relationship with ants, but also exercise natural selection by adapting to their environment.

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One question that might come up is why ants in particular? Out of all the insects in the world, why do phorid flies select ants as their hosts? Since host discrimination is a key part of the process of parasitism, phorid flies choose “social insects,”  such as ants, because of their blunt “ intraspecific chemical communication signals” that come in handy when trying to differentiate between potential hosts and already parasitized ones. In order to search for a host, phorid flies initiate the procedure by tracing the host’s habitat through the use of a host’s preferred environment. Since the phorid fly adapting itself to the host’s natural surroundings or environment, natural selection is explicated. Phorid flies proceed from there by detecting pheromones, which are the method in which ants communicate with themselves and are therefore manipulated as clues for their parasites to locate their potential hosts. Host regulation is established and maintained by even more cues, which include, “movement, host size, and contact chemical cues.” Host regulation is not only significant for parasitizing, but also can influence the success rate of offspring for the flies. Phorid flies hover over the ants, and then attack by inserting an egg underneath the ant’s exoskeleton once the process is close to an end or almost complete.

The effect phorid flies have on ants is noticeable in the fact that host regulation has the potential to “alter(ing) the physiology of the host in an attempt to facilitate growth or even alter(ing) host behavior to optimize nutrient intake or location within the external environment,”which therefore conveys the process of natural selection between the host-parasite relationship of the phorid fly and ant.

Sources: 

http://www.entomology.wisc.edu/mbcn/fea506.html

http://www.hindawi.com/journals/psyche/2012/380474/

http://www.hindawi.com/journals/psyche/2012/380474/

http://www.hindawi.com/journals/psyche/2012/895424/

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