Congratulations to Roseanne Saalfield, the first of several readers who correctly identified the Mystery Photo as a stage in the life cycle of Cedar-Apple Rust (Gymnosporangium juniperi-virginianae Schwein). This rust is a member of the family Pucciniaceae, a group of fungi that contains many species that usually require plants from two different families (usually within a mile of each other) in order to complete their life cycle: one plant from the Cupressaceae family (eastern red cedar, juniper) and the other from the Rosaceae family (crabapple, apple, hawthorn, serviceberry).
The fungus assumes very different forms on each host. On rose family plants, the fungus can be present on the leaves (orange spots on the surface of the leaves and tiny projections beneath them) as well as the fruit. On cedars and junipers, brown spherical galls produce orange, fleshy projections.
For those readers who wish to know the fairly involved details of the life cycle of this fungus, read on: This rust produces four kinds of spores: basidiospores, teliospores, spermatia, and aeciospores. Teliospores are produced on orange, gelatinous telial horns (see bottom photo) which originate from hard, brown galls on red cedars or other junipers, usually in the spring when it’s been raining. Teliospores germinate to form basidia. Basidia produce basidiospores that are released into the air, blown two to three miles potentially to an apple or hawthorn leaf or fruit. They germinate and form a yellow or orange spot on the leaf or fruit (see photo). These spots produce spermogonia that in turn produce spermatia. The spermatia are released into a sticky liquid attractive to many insects. As insects carry spermatia from one spot to the next fertilization takes place. The fungus grows on the fruit or through the leaf and produce aecia on the underside of the leaf (see photo). The aecia produce aeciospores that are windblown back to the red cedars. They then germinate and start the formation of galls that in the following year will produce telial horns to start the process over again. (U.S. Forest Service)
In the spring, the 4mm-long cynipid gall wasp, Diplolepis rosae, lays up to 60 eggs (through parthenogenesis) inside the leaf bud of a rose bush. A week later, the eggs hatch and the larvae begin feeding on the leaf bud. This stimulates the abnormal growth of plant tissue, and a Mossy Rose Gall, covered with a dense mass of sticky branched filaments, is formed. The gall provides the larvae with food and shelter through the summer. In late October, when the Mossy Rose Gall is at its most colorful, the larvae stop eating and pass into the prepupal stage, in which they overwinter inside the gall. In February or March, the prepupae undergo a final molt and become pupae. If the pupae aren’t extracted and eaten by a bird during the winter or parasitized by another insect, adult wasps exit the gall in the spring and begin the cycle all over again.
Galls, abnormal plants growths caused by many agents including insects, are formed during the growing season on the buds, leaves, roots and branches of plants as a response to chemicals or physical irritation. These galls serve as shelters and a source of food for their inhabitants. Blackberry is host to numerous gall-making insects, including mites, midges and gall wasps, and their temporary homes (galls) are more obvious now that Blackberries have lost their leaves. The Blackberry Seed Gall is caused by a cynipid gall wasp, Diastrophus cuscutaeformis. This wasp gets its species name from the resemblance of the galls it forms to the fruit of Dodder or Cuscuta, a parasitic plant. A cluster of small, globular, seed-like galls within which the gall wasp larvae live are pressed together in a lump surrounding the cane. Each of these 1/10th-inch diameter chambers bears a spine, and together they create a reddish-brown hairy mass.