Phenolic-metabolism
Guides
Hormaphis hamamelidis
Witch-hazel Cone Gall Aphid
Hormaphis hamamelidis is a gall-forming aphid that induces distinctive red, cone-shaped galls on witch-hazel (Hamamelis virginiana) leaves. The species exhibits host alternation, with sexual reproduction and gall formation on witch-hazel in spring, followed by migration to birch (Betula) for parthenogenetic summer generations, and return migration to witch-hazel in autumn. Founding females (fundatrices) actively manipulate host plant phenolic metabolism, increasing condensed tannins and decreasing hydrolyzable tannins within galls to enhance their own reproductive success. Gall size, determined largely by fundatrix manipulation of plant growth, is the primary predictor of fundatrix fecundity rather than leaf position or plant vigor per se.