In a striking act of self-sacrifice, infected ant worker pupae send a chemical alert that prompts their nestmates to kill them, safeguarding the colony.
Worker ant pupae infected with a deadly fungus actively produce a chemical signal that triggers their own destruction by colony members, researchers report in Nature Communications. This altruistic signaling, revealed through behavioral, chemical, immunological, and infection load analyses, contrasts with queen pupae, which hold back the infection without signaling.
The study focused on the invasive garden ant, Lasius neglectus, where workers switch from caring for brood to destructively disinfecting fatally infected pupae, unpacking them from cocoons, biting, and applying antimicrobials, to curb disease spread.
To explore if pupae actively signal for this fate, the team infected individual worker and queen pupae with the fungus Metarhizium brunneum or gave sham treatments, then kept them alone or with two workers for up to 42 hours. They analyzed surface chemicals, immune gene expression, and fungal growth.
“Here we show by behavioural, chemical, immunological and infection load analyses that sick ant pupae instead actively emit a chemical signal that in itself is sufficient to trigger their own destruction by colony members,” the study authors note.
Infected worker pupae ramped up two immune-linked cuticular hydrocarbons—C33:2 (tritriacontadiene) and C33:1 (tritriacontene)—only when with workers, deviating their chemical profile from controls and isolated infected pupae. This boost wasn’t tied to fungal load, hinting at host control.
Immune genes for pathogen recognition, regulation, and defense spiked upon infection in both castes, regardless of worker presence. But queens started with 35% higher baseline expression, enabling them to peak and then slash fungal loads nearly threefold late in infection, while workers saw steady fungal climbs.
Queen pupae showed no chemical shifts, and workers didn’t unpack them more than controls, unlike signaling worker pupae.
A bioassay confirmed causality: Coating healthy worker or queen pupae with extract from signaling pupae spurred more unpacking than non-signal extract. Detailed analysis revealed the signal involves not just higher C33:2 and C33:1 levels but shifts in C33:1 isomers.
“Our data suggest the evolution of a finely-tuned signalling system in which it is not the induction of an individual’s immune response, but rather its failure to overcome the infection, that triggers pupal signalling for sacrifice,” the researchers write.
This setup lets pupae try clearing infections solo before signaling doom, balancing personal survival with colony health. The parallels to honeybees suggest unsaturated hydrocarbons as key disease markers in social insects, though specifics vary.
Citations: Nature Communications. DOI: 10.1038/s41467-025-66175-z
