Insurance-based advantage to helpers in a tropical hover wasp

The origin and maintenance of eusociality is a central problem in evolution ary biology(1,2). Eusocial groups contain individuals that forfeit their ow n reproduction in order to help others reproduce. In facultatively eusocial taxa, offspring can choose whether to found new nests or become helpers in their natal groups. In many facultatively eusocial insects, offspring need continuous care during development, but adult carers have life expectancie s shorter than the developmental period(3-7). When a lone foundress dies, h er partly reared brood are usually doomed. Here, we show that helpers in a tropical hover wasp (Liostenogaster flavolineata) have an insurance-based a dvantage over lone foundresses because after a helper dies, most of the bro od that she has partly reared will be brought to maturity by surviving nest -mates. After some of the helpers are experimentally removed from a multi-f emale nest, the reduced group is left with more brood than it would normall y rear. We found that larger, more valuable extra brood were reared through to maturity, but not smaller, less valuable brood. Smaller brood may be sa crificed to feed larger brood, and reduced groups probably benefited from i ncreased short-term helper recruitment. Rearing extra brood did not increas e adult mortality or brood development time.