Solidago galls
There are two types of insects that form galls on Solidago (goldenrod):
Eurosta solidaginis (a fly species) and Epiblema saiddeniana (a moth species).
The fly produces a round, ball-like gall on the stem and the moth produces a more elongate spindle-like gall. The adults lay their eggs on the top of the stem and when the eggs hatch, the larvae burrow down into the stem and induce the plant to form a gall.
The larvae of both of these species overwinter in the galls. This means they must be able to tolerate very cold temperatures. Many other insects would overwinter in the soil or litter where it is much warmer. However, these larvae are able to tolerate very cold temperatures. Much of the damage associated with cold winter temperatures is related to the formation of ice crystals. Water expands when it freezes and this ruptures the cells. Both these species produce antifreeze compounds to prevent the formation of ice. The primary compounds are sorbitol and glycerol. These compounds, just like the ethylene glycol in your car’s radiator, depress the freezing point of water. In the moth species, freezing never takes place. In the fly species, the cells don’t freeze but ice crystals do form in the intercellular spaces and body cavity.
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