SOLDIERS EFFECTIVELY DEFEND APHID COLONIES AGAINST PREDATORS IN THE FIELD

Morphologically specialized soldiers occur in more than 50 aphid speci es in the families Pemphigidae and Hormaphididae. To study the effecti veness of soldiers of the gall-forming aphid, Pemphigus spyrothecae Pa ss., in protecting their galls against natural levels of predation, we manipulated the proportions of soldiers and non-soldiers in sets of g alls still attached to poplar trees in the held. Galls with 50 soldier s and 50 non-soldiers were approximately 10 times less likely to be at tacked by predators than galls that contained 100 non-soldier aphids. There were significantly fewer live aphids, and significantly more dea d aphids, in galls without soldiers than in galls protected either by soldiers or by being within a bag. There were no significant differenc es in the survival of aphids in galls protected by soldiers compared w ith those protected by bagging. The soldiers did not protect the galls against invasion by the cohabiting aphid Chaitophorus leucomelas Koch . These observations provide the first demonstration that soldiers are effective in defence against natural levels of predation under field conditions. (C) 1998 The Association for the Study of Animal Behaviour .