Goldenrod gall fly

Distribution

''E. solidaginis'' is widely distributed across the United States, ranging from Washington all the way to the eastern seaboard. The two subspecies occupy different ranges, with ''E. solidaginis'' subsp. ''solidaginis'' being found from the east coast to Minnesota and the Dakotas, up to the southeastern provinces of Canada, and down the southern border of the United States. ''E. solidaginis'' subsp. ''fascipennis'', on the other hand, can be found as far west as Washington and as far east as Minnesota.

Behavior

Adult ''E. solidaginis'' emerge from their galls in the spring, with the males emerging prior to the females. The flies proceed to mate on goldenrod plants, and the females use their ovipositors to insert fertilized eggs into the buds of the goldenrod.

Though ''E. solidaginis'' has been reported to form galls on seven different species of goldenrod, only three appear to be common targets: ''Solidago canadensis'', ''S. gigantea'' and ''S. altissima''. Once the larvae hatch, typically between 5 and 8 days after the egg is laid, the larva eats its way to the base of the goldenrod bud and induces a gall. These galls serve as food sources and shelters from rain, wind and ice. Despite being the larva’s overwintering structure, the gall itself does not provide significant insulation. Instead, the larva itself has robust freezing tolerance. The larva feeds on the tissues of the gall and molts twice before excavating a narrow exit tunnel out of the gall in mid-September. After digging its tunnel, without actually opening up the gall to the outside, the larva overwinters and, if it survives, molts into an adult and leaves the gall the following spring.

A number of predators and parasites prey on the larvae of ''E. solidaginis''. The black-capped chickadee and the downy woodpecker target large galls, breaking them open and removing the larva living inside. The parasitic wasps ''Eurytoma obtusiventris'' and ''E. gigantea'' also target the gallmaker. The former injects its eggs directly into ''E. solidaginis'' larvae prior to gall formation, whereas the latter oviposits into the gall itself. In both cases, the ''E. solidaginis'' larvae are consumed. There is also ''Mordellistena unicolor'', a beetle whose larvae, after hatching on the surface of a gall, burrow their way in and feed off of its nutritive tissues. ''M. unicolor'' typically kills the ''E. solidaginis'' larva inhabiting the gall, but this does not appear to be an essential part of its life cycle. One of the upshots of these interactions is that larvae that produce galls of a moderate size – that is, not small and thin enough for wasps to easily penetrate, but not large enough to attract the attention of birds – have a fitness advantage. In addition to these direct, predatory interactions, a negative correlation has been observed between goldenrod defoliation by ''Trirhabda'' beetles, suggesting that competition for plant resources may also have an important role to play in the ''Eurosta/Solidago'' system.

Habitat

Adult ''E. solidaginis'' emerge from their galls in the spring, with the males emerging prior to the females. The flies proceed to mate on goldenrod plants, and the females use their ovipositors to insert fertilized eggs into the buds of the goldenrod.

Though ''E. solidaginis'' has been reported to form galls on seven different species of goldenrod, only three appear to be common targets: ''Solidago canadensis'', ''S. gigantea'' and ''S. altissima''. Once the larvae hatch, typically between 5 and 8 days after the egg is laid, the larva eats its way to the base of the goldenrod bud and induces a gall. These galls serve as food sources and shelters from rain, wind and ice. Despite being the larva’s overwintering structure, the gall itself does not provide significant insulation. Instead, the larva itself has robust freezing tolerance. The larva feeds on the tissues of the gall and molts twice before excavating a narrow exit tunnel out of the gall in mid-September. After digging its tunnel, without actually opening up the gall to the outside, the larva overwinters and, if it survives, molts into an adult and leaves the gall the following spring.

A number of predators and parasites prey on the larvae of ''E. solidaginis''. The black-capped chickadee and the downy woodpecker target large galls, breaking them open and removing the larva living inside. The parasitic wasps ''Eurytoma obtusiventris'' and ''E. gigantea'' also target the gallmaker. The former injects its eggs directly into ''E. solidaginis'' larvae prior to gall formation, whereas the latter oviposits into the gall itself. In both cases, the ''E. solidaginis'' larvae are consumed. There is also ''Mordellistena unicolor'', a beetle whose larvae, after hatching on the surface of a gall, burrow their way in and feed off of its nutritive tissues. ''M. unicolor'' typically kills the ''E. solidaginis'' larva inhabiting the gall, but this does not appear to be an essential part of its life cycle. One of the upshots of these interactions is that larvae that produce galls of a moderate size – that is, not small and thin enough for wasps to easily penetrate, but not large enough to attract the attention of birds – have a fitness advantage. In addition to these direct, predatory interactions, a negative correlation has been observed between goldenrod defoliation by ''Trirhabda'' beetles, suggesting that competition for plant resources may also have an important role to play in the ''Eurosta/Solidago'' system.