Social insects such as ants, ter­mites, and some bees and wasps live in a sort of eternal “air­plane envi­ron­ment,” according Rebeca Rosen­gaus, an asso­ciate pro­fessor in Northeastern’s Depart­ment of Marine and Envi­ron­mental Sci­ences. That is, they live in con­fined quar­ters, sharing the same air, food, and even microbes for their entire lives.

Like jet­set­ters, she said, “social insects are exposed to pathogens just like every­body else in the world, but have the added hand­icap of being social.”

Fol­lowing the air­plane analogy, one might sus­pect that sociality would increase the risk of infec­tion, as microbes readily pass from one indi­vidual to the other. But, in fact, Rosen­gaus’ work has shown the exact oppo­site: social insects deal with dis­ease much better when they’re in groups than when they’re isolated.

In pre­vious research, Rosen­gaus’ team showed that the so-​​called “social stomach” of indi­vidual ants, which pro­duces droplets of liquid food to be passed from one adult ant’s mouth to the next, doesn’t just ensure the delivery of nutri­ents to the entire group. It also pro­motes the transfer of immune pro­teins from immu­nized to non-​​immunized mem­bers of the colony.

Rebecca Rosengaus is an associate professor in the Department of Biology. Photo by Brooks Canaday.

Rebeca Rosen­gaus is an asso­ciate pro­fessor in the Depart­ment of Marine and Envi­ron­mental Sci­ences. Photo by Brooks Canaday.

In a paper pub­lished in the journal Biology Let­ters, Rosen­gaus’ team has expanded that research to include an exam­i­na­tion of ant larvae. Given the metic­u­lous grooming that ant larvae receive from workers, as well as the transfer of fluids from the workers’ “social stom­achs” to the larvae, Rosen­gaus hypoth­e­sized that the imma­ture larvae may receive less nat­ural immu­ni­ties and instead focus their energy on growing faster.

It’s costly to pro­duce immune pro­teins, because it takes energy away from you,” Rosen­gaus said. “If you’re a little larva that wants to grow fast and get plump, why should you pro­duce your own immune pro­teins if you’re get­ting the immune goodies from some­body else?”

Rosen­gaus explained that if social transfer of immune pro­tec­tion via mouth-​​to-​​mouth regur­gi­ta­tion were enough, then evo­lu­tion should have reduced the work young ant larvae put into building their own immu­nity. To test this, her team vac­ci­nated larvae by injecting them with killed bac­teria (the same way humans are vac­ci­nated) or a saline solu­tion and then placed them with workers who tended to the larvae. On the third day, the team exposed the larvae to live, more destruc­tive bac­teria. They found that the vac­ci­nated insects were five times more likely to sur­vive the chal­lenge than those unvaccinated.

This con­firmed that ant larvae have retained their indi­vidual immune sys­tems throughout mil­lions of years of evo­lu­tion despite the fact that workers pro­vide exten­sive brood care, Rosen­gaus said, and that imma­ture larvae are indeed capable of immune priming.

The find­ings point to yet another method by which social insects deal with dis­ease. In the age of phe­nomena such as colony col­lapse dis­order among bees and inva­sive fire ant pop­u­la­tions in the southern United States, under­standing the mul­tiple mech­a­nisms of social insect immu­nity is crit­ical, according to Rosengaus.

We’re trying to under­stand the inter­ac­tion between group living and immu­nity at the dif­ferent levels of bio­log­ical com­plexity, from the mol­e­cules, to the pro­teins, to the indi­vidual, to the group, to the society,” she explained. “At every step as you go up the hier­archy of com­plexity, you could expect dif­ferent emer­gent prop­er­ties of an immune system.”

This new research shows that ant larvae can gen­erate an immune response. This indi­vidual capa­bility, together with the social trans­mis­sion of immune func­tion via mouth-​​to-​​mouth regur­gi­ta­tion from workers, helps the entire colony sur­vive path­o­genic challenges.

Inter­est­ingly, Rosen­gaus believes that the social nature of the insects, and the ability to transfer immune pro­teins from one ant to another, may have shaped the phys­ical attrib­utes of the immune pro­teins them­selves. Immune pro­teins, to be effec­tive when shared among nest­mates, need to be robust. They should not degrade easily during the exchanges and should retain antimi­cro­bial activity during and after their transfer. She said the ability to gen­erate immu­nity at the indi­vidual level and the exchange of immune pro­tec­tion between indi­vid­uals in a colony may be one reason why social insects are so geo­graph­i­cally wide­spread and so eco­log­i­cally dominant.