Wino wasp killers

Drosophila melanogaster. Photo credit: Wikipedia.

We have all heard about the possible health benefits of consuming red wine in moderation. An Emory University research team recently discovered that alcohol consumption also imparts benefits for another group of animals...fruit flies! In many households these little insects are viewed as a pesky nuisance, yet even fruit flies have their own pests: parasitoid wasps.

Parasitoid wasps don't just annoy their fly hosts, they kill them. The wasps are attracted to the smell of fermented products such as rotting fruit, where fruit flies reside. Once the female wasp finds a host she will deposit her larvae into a fruit fly maggot. The wasp larvae will develop inside of the fly, feeding on its tissues. After the wasps have matured into adults they will burst out of the dying fly's body.

The parasitoid wasp Leptopilinia boulardi. Photo credit: www.scitechdaily.com

What is a fruit fly to do? There are no urgent care clinics, but they do have a sort of "fly pharmacy" on hand. Fruit flies frequently dine on bacteria and yeast found in rotting fruit, and this meal is often accompanied by booze, ethanol to be exact. While the ethanol is a waste product of sugar-consuming yeasts, Dr. Todd Schlenke and his colleagues suspected that it could be a potent anti-parasite medication for fruit flies.

Schlenke and his team performed a series of experiments to test their hypothesis. They used Drosophila melanogaster (fruit fly host) and two different species of parasitoid wasp: Leptopilina heterotoma (generalist parasite of many Drosophila species) and Leptopilina boulardi (specialist parasite of Drosophila melanogaster).  First, the wasps were allowed to attack fly hosts from two different groups: larvae fed a non-alcoholic diet and larvae fed a six percent ethanol diet. Larvae reared on the ethanol diet harbored significantly fewer wasp eggs that did non-alcoholic larvae.

Next, the wasps were allowed to attack fly hosts from both groups to determine how host diet influenced wasp development. Wasps developing in alcohol free larvae thrived while over 60 percent of wasps in the ethanol flies died. Further, the internal organs of the less fortunate wasps had shot out of their anuses: what a way to go.

Infected fly larvae. Photo credit: www.scitechdaily.com

Schlenke and his team noticed that the timing of host alcohol consumption was key for a therapeutic effect; infected flies that subsequently drank alcohol fared well while those that switched to ethanol free diets after becoming parasitized experienced little benefit. They wondered if the flies were actively seeking alcohol to treat their infections. To test this hypothesis, the team placed parasitized and unparasitized fly larvae in bisected petri dishes that contained one side with ethanol free food and the other with ethanol rich food. First, both groups were placed on the ethanol free side. While just over 30 percent of the healthy flies migrated to the ethanol food, a whopping 80 percent of infected flies headed for the booze. They repeated the experiment, but this time they placed both fly groups on the ethanol rich side. Forty percent of the healthy flies switched to the non-alcoholic side, while some of the parasitized flies briefly left only to return to the ethanol side after 24 hours. These data suggest that the flies are deliberately seeking alcohol for therapeutic use!

Another cool aspect of their study was that the wasp species responded to the ethanol in different yet predictable ways. The generalist wasps were much harder hit by the alcohol, while the wasp specialists were more resistant. This is what we would expect given what we know about host-parasite coevolution; the generalists can go on to infect a wide range of hosts, while the specialists are much more restricted, thus there is stronger pressure on them to circumvent this anti-parasite strategy.

While we know that wild animals self-medicate when exposed to pathogens, this is the first study to demonstrate the use of alcohol as a medicine in wild animals. Since alcohol can be found in many natural habitats it is possible that other animals also use it to treat their infections. Lastly, more work is needed to determine if that glass of wine is also helping us to reduce our parasite loads!

Find out more about the flies, the wasps, and about anti-parasite behavior:

Neil F. Milan, Balint Z. Kacsoh, and Todd A. Schlenke. 2012. Alcohol consumption as self-medication against blood-borne parasites in the fruit fly. Current Biology 22: 488-493.

 http://dx.doi.org/10.1016/j.cub.2012.01.045

Brian Gray, Anne C. Jacobs, Adrienne B. Mora, and Marlene Zuk. 2012. Anti-parasite behavior. Current Biology 22: R255-R257.

http://dx.doi.org/10.1016/j.cub.2012.02.024

Parasite profile: The "brain-eating" Naegleria fowleri

Naegleria fowleri is a parasitic amoebo-flagellate that infects humans, causing severe illness and in many cases, death. This single-celled protist can be found in warm freshwater bodies, soil, and various contaminated water sources.

 Photo credit: www.soakersforum.com

Life Cycle


Naegleria fowleri can exist in three different forms during its life cycle: a cyst, a trophozoite, and a flagellate. The cyst is environmentally resistant and can protect the parasite during periods of poor environmental conditions. Once favorable conditions return, the parasite excysts as a trophozoite where it feeds and reproduces via binary fission. The trophozoite can then go on to the encysted or free-swimming flagellated form.

Life cycle stages for  N. fowleri from left to right: Cyst, trophozoite, flagellate. Photo credit: Wikipedia

How do people become infected?

Humans can become infected with N. fowleri when swimming in lakes, ponds, or untreated swimming pools, playing water sports, or even when irrigating sinuses with contaminated water. In addition, it is purported that inhaling viable cysts in dust can also lead to infection. Once the parasite contacts the nasal epithelium, it travels up the nasal mucosa and to the brain through the olfactory nerves.

Photo credit: Centers for Disease Control and Prevention

Symptoms, diagnostics, and treatment

    

Once the parasite enters the brain, it causes primary amebic meningoencephalitis (PAM), which is fatal in almost all cases. 

The onset of PAM is characterized by the following symptoms:

-fever

-headache

-changes in sense of smell or taste (due to destruction of the olfactory bulbs)

-stiff neck

-sensitivity to light

-changes in mental status

-seizures

-coma

-death  

Cerebrospinal fluid or tissue samples may be collected and analyzed for the presence of trophozoites. Treatment usually consists of administering high doses of amphotericin B and miconazole, although it is suggested that the rapid progression of infection makes successful treatment very difficult. As such, patients exhibit a high mortality rate.

Find out more about Naegleria fowleri:

Centers for Disease Control:
http://www.cdc.gov/parasites/naegleria/

National Society for Biotechnology Information:
http://www.ncbi.nlm.nih.gov/books/NBK7960/

Medscape:
http://emedicine.medscape.com/article/223910-overview

Zombifying flies and their honeybee hosts

Honey bees around the world have been dying at alarming rates, creating widespread concern and bafflement among both public and scientific communities. In the United States, symptoms of these impending declines are collectively referred to as Colony Collapse Disorder, or "CCD". CCD is primarily characterized by hive abandonment, where no or few honeybees are present in a hive even though a live queen remains.  While many factors contribute to bee declines such as mites, viruses, bacteria, fungi, and pesticides, Dr. John Hafernik, a biology professor at San Francisco State University, discovered another contender by accident: the parasitoid fly Apocephalus borealis. With the help of colleagues and his graduate student Andrew Core (the lead author), the team worked to figure out this mysterious host-parasite relationship. Recently, their fascinating findings were published in pLoS one.


It turns out that female A. borealis flies will locate honeybee hosts and land on them, depositing their eggs or "ovipositing" them into the bee's abdomen. The fly larvae develop inside of the bee and approximately seven days later they emerge, killing the bee in the process. This is very reminiscent of the movie "Aliens" isn't it?

The parasitoid fly and it's honeybee host. A) An adult female Apocephalus borealis fly. B) A female A. borealis fly deposits eggs into the abdomen of a honeybee (note how small the fly is). C) Two A. borealis fly larvae exiting the host. Photo credit: Core et al. 2012.

The even more curious thing is that the parasitized bees exhibit very unusual behavior before fully succumbing to the parasites. They abandon their hives at night; healthy bees usually leave their hives during the day to forage. They wander about aimlessly in circles, appearing disoriented and unable to properly balance. Moreover, the bees become attracted to light at nighttime. Core and colleagues suggest that the parasites may manipulate the light sensitivity or circadian rhythm of their hosts in some way, but more work is needed to fully investigate these possibilities.


The troubling realization from all of this is that honeybees usually occur in high densities, and colonies are often found in close proximity to each other. These conditions could make it very easy for fly populations to boom and further decimate honeybee populations that are already in decline. Honeybees are crucial for the pollination of many plants and agriculturally important crops, and for the production of their highly prized honey.  Research conducted by groups such as Core and colleagues is vital to the preservation of these important insects.

Find out more about colony collapse disorder:

USDA Agricultural Research Service

http://www.ars.usda.gov/News/docs.htm?docid=15572

Environmental Protection Agency:
http://www.epa.gov/pesticides/about/intheworks/honeybee.htm


Bromenshank et al. 2010:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013181