Apple oak gall (Amphibolips confluenta or Amphibolips quercusinanis), backlit to show leaf-like venation. Second photograph is a cross section showing where the wasp larva develops. I’d love to know what the spotting does, if anything.
Cynipid wasps love oaks for some reason — over 3/4 of the 1300 species use Quercus as host. People argue about why that’s the case (e.g., Ronquist et al. 2015). Even Alfred Kinsey the sexologist weighed in, back in the days when he was obsessed with gall wasps.
Below are some photographs of strange growths on a patch of Asclepias syriaca I visited several weeks ago. From the few publications I’ve found, enations can be caused by viruses (Geminiviridae, Luteoviridae, etc.), and thus could be transmitted to nearby individuals via insect vectors or by the connected roots (milkweeds are clonal). Could be a genetic mutation, too, I suppose — could be spread by seed or via clonal growth. Anyone seen this before?
Photographed at Hildacy Farm Preserve in Media, PA.