Self-sacrificing gall repair by aphid nymphs.

Insect galls are vulnerable to invasion by moth larvae that can tunnel into the wall. We report that nymphs of the aphid Nipponaphis monzeni repair their gall self-sacrificingly. When a hole was bored into their gall, many globular nymphs discharged a large amount of body fluid from their cornicles onto the gall's wound, and kneaded the fluid, which soon became viscous and eventually congealed, plastering over the hole. Having discharged the fluid, the nymphs shrivelled to approximately one-third of their original volume. Several nymphs were buried in the plaster, like 'aphid sacrifices'. This is the most elaborate social behaviour so far known among aphids.