Fruit flies cells activate antimicrobial molecules as a precaution against infection in times of energy shortage.


From the largest whale to the tiniest bacterium, hunger and disease are two of life’s biggest threats. Both play a role in a unique survival strategy of the fruit fly (Drosophila melanogaster). When a fruit fly is stressed by hunger, its cells automatically start producing a type of compound that destroys bacteria and other pathogens. This reduces the likelihood that microbes can take advantage of the fly’s hunger-caused low-energy to launch a full-bore invasion.

The Strategy

Hunger creates stress for an organism by reducing the amount of energy available for keeping its organs and tissues humming along. This reduced energy in turn makes the organism more vulnerable to invasion by bacteria and other illness-causing organisms—similar to the way humans are more likely to make mistakes when we’re tired or distracted by problems we’re trying to solve or difficulties we’re trying to deal with.


The fruit fly reduces the risk of having one difficulty (hunger) lead to another (infection) by starting a cause‑and‑effect chain reaction of its own.

The fruit fly reduces the risk of having one difficulty (hunger) lead to another (infection) by starting a cause-and-effect chain reaction of its own. At the center of this operation is a category of molecules known as antimicrobial s, or AMPs. Unlike many immune system actors, these molecules are not tailored to specific pathogens. Rather, they attack and kill whatever bacteria they encounter, wherever they encounter them, by demolishing their cell walls. Since some bacteria are beneficial, you don’t want AMPs around everywhere, all of the time. But they’re a valuable asset to be able to produce when absolutely needed.

When hunger reduces the energy level within cells, levels of , also drop. This signals a chemical known as FOXO to enter the cell’s nucleus. Once in the nucleus, FOXO turns on the genes that make AMPs. These newly minted AMPs are then available to destroy pathogens, should any try to take advantage of the fly’s hunger-induced vulnerability.

While this is all well documented among fruit flies specifically, AMPs are found in many plants and animals, including humans. A similar mechanism could come into play when we are stressed, too.

The Potential

It’s easy to imagine that the right response when times get tough is to slow down other activities and focus on the stress. The fruit fly’s innate system for ramping up defense mechanisms under stress provides a template for using stress as a signal that it’s time to take preemptive actions to minimize the adverse consequences that might emerge from the stressed conditions. By responding to conditions that signal a potential increase in vulnerability, the fly preemptively fortifies itself against potential enemies.

The take-home lesson for humans: Rather than focusing exclusively on dealing with immediate sources of stress, also be mindful of what other, future stresses the current challenge might and take preventive actions to avoid being buried in an avalanche of snowballing stresses down the road.

Fruit fly on a banana
Image: Sanjay Acharya / Wikimedia Commons / CC BY SA - Creative Commons Attribution + ShareAlike

Fruit flies illustrate an important principle of dealing with stress: Consider, and take preventive actions against, follow‑on problems, too. 

Drosophila gut cells
Image: Gerit Linneweber / Flickr / CC BY - Creative Commons Attribution alone

When stressed by hunger, the cells that line the gut of a fruit fly’s digestive tract begin producing antimicrobial molecules that prepare it to fight off pathogens that might take advantage of its weakened state.

Last Updated September 14, 2016