Aphids Do Home Repair
Hole in a gall has been repaired by soldier aphids (white dots).
Credit: Mayako Kutsukake

Social aphids have a soldier caste whose recruits may tackle civic projects as well as military operations.

Take Nipponaphis monzeni, which induces tree twigs to grow hollow, woody balls called "galls." The aphid colonies live inside those galls and feed on the plant material within. If a gall becomes damaged, a new study shows, soldiers can help the plant heal it.

A hole in a gall can expose a colony to desiccation or predator invasion. A few years ago, three researchers, including Takema Fukatsu at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, reported that when a hole appears in a gall wall, soldier aphids emerge and discharge body fluids into the breach to plug it.

The soldiers get stranded outside. Some get stuck in the plug. All perish.

Back inside the gall, other soldiers continue the repair work for many days, Fukatsu, Mayako Kutsukake, and two colleagues have now shown. By periodically inspecting wounded galls, the team found that the soldiers plaster more body fluid onto the plug's interior surface to maintain the seal, and then stimulate the surrounding plant tissue to grow and eventually to replace the plug. Just how the aphids get the tree to mend itself remains unknown, but a gall won't heal if the aphids inside are killed.

The observations show that some aphids have a degree of job specialization comparable to the more celebrated insect societies of bees, ants, and termites.

The findings were detailed in Proceedings of the Royal Society B.