Trophallaxis in a primitively social sphecid wasp

Summary In a total of six hours of observation of severalMicrostigmus nigrophthalmus nests with two or more adult wasps, nine buccal contacts, six between females and three between females and males were observed. Except for two cases, these occurred soon after one of the females involved (the apparent donor) had returned to the nest and involved transfer from older to younger individuals. Experimental feeding of colored solution confirmed the occurrence of trophallaxis. InM. nigrophthalmus, trophallaxis seems to have arisen as a prolongation of maternal care since food is transferred from an older to a younger individual.