Defensive nymphs and water-repellency in previously unknown galls of the social aphid Colophina monstrifica (Hemiptera: Aphididae: Eriosomatinae)

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 Zelkova serrata by attaching its eggs to 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 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 suggests that young nymphs of C. monstrifica dispose of honeydew globules outside the gall, as known in the congener Colophina clematis.