Weird Willow Gall

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Arguably, one of the weirdest galls found in Ohio is produced on willow by the gall-midge, Rhabdophaga strobiloides (family Cecidomyiidae).  The gall's appearance isn't weird; it looks like a pine cone.  However, finding a "pine cone" on a willow is weird.  As the common name implies, the Willow Pinecone Gall, which is sometimes called the "pine cone willow gall," closely resembles a pine cone with closed seed scales.


Willow Pinecone Galls


Females initiate gall formation when they lay a single egg in terminal buds in the spring.  Chemicals injected by the female coupled with chemicals exuded by the egg and then by the resulting larva (maggot) direct the stem tissue to stop elongating and the nascent leaf tissue to broaden and harden into the shape of scales on a pine cone.  Early-season galls are ball-like; late-season galls are cone-shaped.


Willow Pinecone Gall


Slicing the gall open lengthwise will reveal a single, midge fly larva housed in an elongated chamber at the center of the gall structure and protected by multiple layers of cone-like scales.  Early instar larvae are yellowish-white but they become yellowish-orange as they molt through successive instars.  Mature larvae spend the winter inside their protective chamber.  Pupation occurs in early spring with the new adults emerging from the top of the gall to initiate the formation of new galls.