The witch-hazel cone gall aphid (''Hormaphis hamamelidis'') is a minuscule insect, a member of the aphid superfamily, whose presence on a

witch-hazel Witch-hazels or witch hazels (''Hamamelis'') are a genus of flowering plants in the family Hamamelidaceae, with three species in North America ('' H. ovalis'', '' H. virginiana'', and '' H. vernalis''), and one each in Japan ('' H.&n ...

(''Hamamelis virginiana'') plant is easily recognizable by a conical

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...

structure. The gall is green at first, then turns bright red. This gall, rich in nutrients, provides both food and shelter for the female aphid. Hormaphis hamamelidis gall

''H. hamamelidis'' have three generations per year, each with a different part in the life cycle. At the start of spring, females or ''stem mothers'' crawl to witch-hazel leaf buds. As the leaf grows, the aphid injects it with a substance, possibly an

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

, that causes that the galls to form around her. Once inside her gall, the stem mother reproduces parthenogenically and fills the gall with 50–70 female offspring. The second generation develops wings and disperses, repeating the process. The third generation includes both males and females. Towards the end of summer, the third generation reproduces sexually and lays eggs on the bark of the witch-hazel. The cycle begins anew in the following spring. ''Hormaphis hamamelidis'' is sometimes mistaken with ''

Hormaphis cornu ''Hormaphis'' is a genus of witch hazel and palm aphids in the family Aphididae. There are at least three described species in ''Hormaphis'', found mainly in eastern North America. Species These three species belong to the genus ''Hormaphis'': * ...

''. The two are closely related, both live in the eastern US, and both form galls on witch-hazel. However, while ''H. hamamelidis'' is

autoecious A heteroecious parasite is one that requires at least two Host (biology), hosts. The ''primary host'' is the host in which the parasite spends its adult life; the other is the ''secondary host''. Both hosts are required for the parasite to compl ...

and has three generations in a year, ''H. cornu'' lays eggs on both witch-hazel and river birch and has seven generations in year. ''H. hamamelidis'' is often found at higher elevations, while ''H. cornu'' is typically observed at lower elevations. The two species readily interbreed, but hybrids are probably inviable. Like galls formed by other insects, the galls of ''H. hamamelidis'' may deter herbivory.

Life history

The first generation of the year is composed entirely of female fundatrices (also called stem mothers), which hatch from winter eggs laid on the bark of witch-hazel. Shortly following bud break, she begins to feed on leaf tissue. She then repeatedly “stings” the abaxial surface of the leaf to induce gall formation. A gall forms around her approximately 7–14 mm tall on the adaxial (upper) side of the leaf. She then reproduces around 45 female offspring through parthenogenesis. The second generation consists of alate sexuparae, which are winged females. As the second generation matures within the gall, the stem mother and juveniles feed on witch-hazel phloem and push waxy detritus through the gall opening on the leaf's underside.Lewis, I. F. & Walton, L. (1958). Gall-Formation on Hamamelis virginiana Resulting from Material Injected by the Aphid Hormaphis hamamelidis. ''Transactions of the American Microscopical Society'', ''77''(2), 146. All the offspring from a given gall mature at the same time and become winged migrants. At maturity, the females leave the gall and begin to lay the eggs of the third generation on surrounding leaves, often on the same plant that they emerged from. The third generation comprises both male and female sexuales. Individuals begin mating after their final molt. Mating may occur on the leaves where the aphids hatched or on the plant's winter buds. There, females deposit between five and ten eggs, which remain throughout the winter.

Gall formation

The process of “stinging” the leaf to induce gall formation is distinct from normal feeding behavior. While feeding occurs seemingly haphazardly, a stem mother must repeatedly sting a site over some time to induce gall growth. When stinging, the aphid repeatedly inserts her stylets into the leaf over a small circular area. She injects a substance produced in glands near the stylar canal. This substance is distinct from saliva, and the cells of the leaf respond rapidly. Higher fecundity is linked to larger gall size, as well as increased levels of condensed tannins. Galls also have higher vacuolar invertase activity than surrounding leaf tissue, and greater cell wall invertase activity is positively correlated with fecundity.Rehill, B. J. & Schultz, J. C. (2003). Enhanced Invertase Activities in the Galls of Hormaphis hamamelidis. ''Journal of Chemical Ecology'', ''29''(12), 2703–2720.

References

External links

"Biting the Plant that Feeds You"Article on gall-forming aphidsSpecies ''Hormaphis hamamelidis'' - Witch Hazel Cone Gall Aphid
Hormaphidinae Insects described in 1851 Taxa named by Asa Fitch Hemiptera of North America Gall-inducing insects {{Aphididae-stub