Fortress repair in the social aphid species Pemphigus spyrothecae

Nest repair is a vital element in the cooperative brood care that is a distinctive feature of eusocial animals. We investigated the repair role of individuals of the social aphid Pemphigus spyrothecae by prematurely opening their gall by cutting a hole of the same size and position as a natural opening. This resulted in increased mortality from predation. No subsequent responsive shift towards increased investment in soldiers was detected. However, repair of the holes by compensatory regrowth from undamaged adjoining areas of the gall was observed in 97.5% of the experimental galls that were protected from predation. Subsequent experiments confirmed that the aphids were responsible for this repair, with soldiers likely to be the major agents. Active maintenance of the integrity of the gall represents another altruistic task for which soldiers are predominantly responsible and indicates that social complexity in the order Hemiptera is greater than previously assumed.