'Body eruption': the aphids that sacrifice themselves for colony

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Scientists study species that releases huge quantities of bodily fluids to plug nest holes

Aphids sacrifice themselves to protect colony from predators - video

While humans might change their locks to deal with intruders, a species of aphid opts for a communal sacrifice, releasing huge quantities of a sticky bodily fluid to plug holes in their nests.

Researchers who studied the makeup of the fluid found the process for nest repair was similar to what happens when aphids are wounded, involving the release of substances that clot and form a scab. This means similar mechanisms underpin both individual immunity and so-called social immunity – when organisms work together to protect their communities from enemies and disease.

“The mechanistic bases of social immunity, which are mainly behavioural, physiological and organisational ones, are expected to be distinct from the molecular and cellular immune mechanisms,” said Dr Takema Fukatsu, a co-author of the research from the National Institute of Advanced Industrial Science and Technology in Japan. “In this context, our finding was quite unexpected and surprising.”

When predators break into the growths, or galls, on winter hazel trees that house the aphid Nipponaphis monzeni, “soldier nymphs” of the species gather to sting the invader and repair the damage. The breach is patched up with a white gunge, released by the soldier nymphs in what the team call a “body eruption”.

“Dozens of soldiers come out, erupt, mix and plaster, and the gall breach is promptly sealed with the coagulated bodily fluid,” the authors write in the journal Proceedings of the National Academy of Sciences. The shrivelled aphids use their legs to mix the fluids.

The soldier nymphs run the risk of being left outside or suffocated by their own goo, while even those that initially survive the body eruption are likely to die soon after. “It is unlikely that the tiny soldiers that have lost almost all body fluid can survive long,” said Fukatsu.

In the latest study, the team has discovered that the bodily fluid contains a cocktail of chemicals and is particularly rich in lipids that are released from a type of insect immune cell that disintegrates within the fluid after the body eruption. This allows them to patch up the breach in a sort of “soft plug” that hardens and becomes black over time. Gradually plant tissue grows and covers the area, completely sealing it up.

The results suggest the soldier nymphs have boosted levels of production of particular cells and substances involved in clotting and scab formation, meaning a mechanism initially developed for wound healing in individuals may have been adapted to become a key process in defending the entire colony.

“We are not sure that the body fluid coagulation mechanisms in the soldier nymphs are exactly the same as that [for wound healing] in normal aphids, but suppose that the mechanisms are fundamentally the same,” said Fukatsu.

“In most cases, the self-explosive behaviours to discharge the body fluid are for entangling and immobilising enemies. It is quite exceptional that such behaviours are utilised for nest [or] gall repairing. I don’t know other cases in the insect world.”