Fruit Flies, Ethanol, Good Health & Biocontrol

March 19, 2012

SEXUAL DEPRIVATION INCREASES Ethanol Intake in Drosophilia” was the semi-tabloid headline in the American Association for the Advancement of Science (AAAS) journal Science (16 March 2012; v. 1355, p. 1351). No fools, the AAAS knows a scientific title readily translatable into good headlines and writerly fun; parental Internet filters be damned. I was particularly impressed by Scientific American Science Sushi blog writer Christie Wilcox’s entertainingly deft mix of science, human implications and fun stuff on fruit flies with quotes from lead scientist Gilat Shohat-Ophir.

You Tube has an entertaining mix of titles on the subject, such as: 1) Flies turn to drinking after sexual refusal; 2) Study: Rejected Male Flies Turn to Alcohol; 3) Scientists Find Fruit Flies Self Medicate With Booze; and from Emory University, 4) ‘Drunken’ fruit flies use alcohol as a drug. The underlying science has a certain fascination, as there are similar neural (molecular) pathways for rewards and addiction (and their interaction with social experiences) in the two species: neuropeptide F (NPF) in fruit flies and neuropeptide Y (NPY) in humans. “Flies exhibit complex addiction-like behaviors,” write Shohat Ophir and colleagues K.R. Kaun, A. Azanchi and U. Heberlein, including “a preference for consuming ethanol-containing food, even if made unpalatable.”

In primitive natural settings, ethanol from fermentation of overripe fruit functions as a cue or lure for humans, fruit flies and other animals to locate fruit crops. Indeed, there is evidence that fruit fly larvae “have evolved resistance to fermentation products” from millennia of eating “yeasts growing on rotting fruit.” But fruit flies are not immune to alcohol-related mortality; the dose of the poison (alcohol) determining whether it is medicinal.

“The high resistance of Drosophila melanogaster (fruit fly) may make it uniquely suited to exploit curative properties of alcohol,” wrote Emory University’s Neil Milan, Balint Kacsoh, and Todd Schlenke in an article titled “Alcohol Consumption as Self-Medication against Blood-Borne Parasites in the Fruit Fly” in Current Biology (2012). “Ethanol levels found in natural D. melanogaster habitats range up to 6% ethanol by volume in rotting fruits, and 11% in wine seepages found at wineries. Fly consumption of food with moderate levels of ethanol (i.e., less than 4% by volume) results in increased fitness, but consumption of higher ethanol concentrations (i.e., greater than 4%) causes increasing fly mortality.”

One of the hazards of life for fruit flies is parasitic wasps, which sting the flies and lay eggs hatching into parasitoid larvae living inside and eventually killing the fruit fly. From the fruit fly’s perspective, biological control by natural enemies is deleterious and best prevented or overcome. “We have shown here that ethanol provides novel benefits to flies by reducing wasp infection, by increasing infection survival, and by allowing for a behavioral immune response against wasps based on consumption of it in toxic amounts,” wrote Milan and his colleagues. “To our knowledge, these data are the first to show that alcohol consumption can have a protective effect against infectious disease and in particular against blood-borne parasites. Given that alcohols are relatively ubiquitous compounds consumed by a number of organisms, protective effects of alcohol consumption may extend beyond fruit flies. Although many studies in humans have documented decreased immune function in chronic consumers of alcohol, little attempt has been made to assay any beneficial effect of acute or moderate alcohol use on parasite mortality or overall host fitness following infection.”

Scientists and students with science projects have been rearing fruit flies for over a century, and unraveling many of the mysteries of biological life. Indeed, the common fruit fly, “Drosophila melanogaster is emerging as one of the most effective tools for analyzing the function of human disease genes, including those responsible for developmental and neurological disorders, cancer, cardiovascular disease, metabolic and storage diseases, and genes required for the function of the visual, auditory and immune systems,” wrote Ethan Bier of the University of California, San Diego, in Nature Reviews Genetics (v.6, Jan. 2005). Depending on the matching criteria, anywhere from 33% to “75% of all human disease genes have related sequences” in fruit flies. Thus, “D. melanogaster can serve as a complex multicellular assay system for analysing the function of a wide array of gene functions involved in human disease.”

Something to think about next time you see those tiny (1/8 inch; 3 mm) golden or brownish fruit flies flitting around your overripe bananas, vegetable-laden bins and garbage cans.