Young aphids sacrifice themselves to make home repairs
Home renovation is never easy. Watch one of those shows on HGTV and you’ll see. But be glad you’re not a young aphid. For them, the cost of being dispatched to patch up a home can be death.
Nipponaphis monzeni is a tiny East Asian aphid. It makes its home in Asian winter hazel trees. Hundreds or thousands of the insects will share a hard-shelled, closed lump called a gall. The fragile insects induce the trees to make that gall, which will protect their colony. But sometimes a predatory caterpillar will chew into the wall to get at the aphids. At once, white wingless youngsters, called soldiers, rush to the breach.
Some mob and sting the intruder. Others get on to patching the hole. Swollen almost to bursting with fluids, these soldiers work as part repair crew, part repair goo. The tiny fluffs of juvenile aphids gush white glop from their bodies. They use this goo to repair a hole in the gall’s wall. New details of this patching chemistry suggest that the doomed young soldiers — each just a half-millimeter (0.2-inch) long — are their colony’s version of immune-system cells.
Researchers described the soldiers repair tactics in the April 30 Proceedings of the National Academy of Sciences.
The glue’s chemistry
Takema Fukatsu is an evolutionary biologist at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan. Near the rear end of each aphid is a pair of openings, called cornicles. The soldiers exude huge (in aphid terms) white gobs of fatty substances and other compounds, Fukatsu notes. The insects then use this goo to help plaster shut a hole.
Some aphids get stuck in the hardening patch and die there. Some perish when they get marooned outside the gall. As for the rest, releasing so much fluid shrivels the youngsters down to about a third of their original body size. That means “the soldiers must die sooner or later,” Fukatsu says.
Until needed, the repair substances normally stay inside the aphids’ bodies. The fatty goo sits in large cells that also hold an enzyme. The two compounds don’t become building “plaster” until after they get squirted out of the aphid’s body. As they burst from their cells, these compounds mix with the insect version of blood and find partners they react with. This thickens the goo.
The doomed youngsters will work the goo as if stomping grapes to make wine. The fatty substances then clot. Eventually, they will darken and harden into an effective patch. Like immune-system cells flooding a skinned knee, the aphid soldiers create a scab.
And they do it fast. A soldier releases about 0.01 to 0.03 microliter of goo in a one-time-only discharge. Yet drop by drop, the emergency crew can scab over a pinhead-sized hole in about 30 minutes.
This is not the only aphid species to use the bodies of colony members as defense tools. Young cabbage aphids (Brevicoryne brassicae) build up a mustardy toxin in their bodies. Crushing or biting one of these soldiers releases a nasty mouthful. The compound also works as an alarm signal that can benefit other aphids. This species is not closely related to the scab makers, says Carol von Dohlen. She’s an evolutionary biologist at Utah State University in Logan. These cabbage aphids evolved their defense chemistry independently.
Tiny as they are, von Dohlen notes, “aphids are surprising.”
caterpillar The larval stage of moths and butterflies. Somewhat wormy-shaped crawlers, caterpillars tend to eat leaves and other plant bits. Some will, however, dine on other insects.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells. Most organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
chemical A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemistry The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.
clot (in medicine) A collection of blood cells (platelets) and chemicals that collect in a small region, stopping the flow of blood.
compound (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
cornicles Tubes that rise up from the lower end of an aphid’s body. The insects release substances, such as pheromones or defensive compounds, through these cylindrical projections.
evolutionary biologist Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).
fat A natural oily or greasy substance occurring in plants and in animal bodies.
gall (in plants) An abnormal growth, often caused by insects, fungi or other plant pests.
immune system The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.
insect A type of arthropod that as an adult will have six segmented legs and three body parts: a head, thorax and abdomen. There are hundreds of thousands of insects, which include bees, beetles, flies and moths.
juvenile Young, sub-adult animals. These are older than “babies” or larvae, but not yet mature enough to be considered an adult.
Proceedings of the National Academy of Sciences A prestigious journal publishing original scientific research, begun in 1914. The journal's content spans the biological, physical, and social sciences. Each of the more than 3,000 papers it publishes each year, now, are not only peer reviewed but also approved by a member of the U.S. National Academy of Sciences.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
toxin A poison produced by living organisms, such as germs, bees, spiders, poison ivy and snakes.
Journal: M. Kutsukake et al. Exaggeration and cooption of innate immunity for social defense. Proceedings of the National Academy of Sciences. Vol. 116, April 30, 2019, p. 8950. doi: 10.1073/pnas.1900917116.
Journal: E. Kazana et al. The cabbage aphid: a walking mustard oil bomb. Proceedings of the Royal Society B. Vol. 274, July 10, 2007. doi: 10.1098/rspb.2007.0237.