In my previous post (see “Manzanita Leaf Fungus” on 08-20-2019), I discussed a manzanita (Arctosstaphylos ssp) gall caused by a fungus. An aphid, the manzanita leaf gall aphid (Tamalia coweni), also induces galls on manzanita shrubs.
T coweni has an interesting, complex life cycle and causes two types of galls on glabrous (no hairs) species of manzanitas. In the spring a mature aphid, called a stem mother or fundatrix, emerges, initiates a gall and reproduces parthenogenically (asexually). The stem mother’s offspring develop into alates, winged females. The females then induce galls which produce male and female alates that mate and deposit eggs. The eggs overwinter and begin the cycle again the following spring.
In the spring the manzanita leaf gall stem mother selects a row of cells on a leaf and stings the cells causing the outer edge of the leaf to fold over one time and gall, enveloping the aphid. These galls on the leaf margins are succulent and red. Once in the gall the stem mother produces wingless female alates.
In July the wingless females seek out developing manzanita inflorescences, which would blossom the next spring. These wingless females resemble the stem mothers.
The wingless females induce pink-red, swollen “bag” galls in the flower bud. The alates that emerge from the bud galls pass through another stage and become males and females. They mate and deposit their eggs in the crevices of bark at the base of the manzanita shrub. The eggs overwinter and a new generation of stem mothers emerge in the spring to begin the life cycle anew.
By using two different host cell sites (leaves and developing flower buds) it is thought the manzanita leaf gall aphid is able to complete the many stages of its life cycle in one year. I am always amazed at the complexity of these tiny insects’ life cycle.
T coweni is found in the Pacific States, Colorado, Nevada and British Columbia.
The leaf galls were photographed along Modoc National Forest Road 40N11 near Adin CA (Modoc County). The bud galls were on manzanitas growing beside Spence Mountain South Ridge Trail near Klamath Falls OR (Klamath County).