Defensive nymphs in the water-repellent gall of the social aphid Colophina monstrifica (Hemiptera: Aphididae: Eriosomatinae)

Abstract

The aphid Colophina monstrifica forms woolly colonies with sterile soldiers on the secondary host Clematis uncinata in Taiwan. However, the gall or primary-host generation of C. monstrifica has not been found to date. We successfully induced galls of the species on trees of Zelkova serrata through attaching its eggs onto the trees, and also found a few naturally formed galls on another Z. serrata tree. The identity of the aphids was confirmed by examining their morphology and mitochondrial DNA sequences. First- and second-instar nymphs in the galls exhibited attacking behavior toward artificially introduced moth larvae. Observations with a scanning electron microscope revealed that the gall inner surface was densely covered with minute trichomes. This indicates the water repellency of the inner surface, and strongly suggests that young nymphs of C. monstrifica dispose of honeydew globules outside the gall, as known in the congener C. clematis.