Effects of burning and burn season on the interaction between <em>Solidago altissima</em> and gallmaking insects

Abstract

The complex interactions between plants and insects are commonly investigated on the Iowa prairie. Abiotic factors affect the success of host plants while insects adapt to take advantage of their hosts' relative success. While many plant-insect relationships fit this description, the close interaction between galling insects and their host plants makes them of particular interest. After a galling insect deposits its eggs into a host plant, the eggs release chemicals that induce the formation of a bulge in the stem. The larvae typically develop for a year inside the bulge before they emerge as adults. Because the reproductive success of galling insects is dependent on their ability to successfully use their host plant, the environmental factors that affect the abundance and size of their host plant indirectly affect the galling insects. We chose to observe the relationship between the common prairie plant, Solidago altissima (Tall Goldenrod,) and its three gall makers, Eurosta solidaginis (Diptera: Tephritidae), Gnorimoschema gallaesolidaginis (Lepidoptera: Gelechiidae) and Rhopalomyia solidaginis (Diptera: Cecidomyidea) in the seasonal burn treatments at the Conard Environmental Research Area (CERA). Each species of gall maker has a unique reproductive cycle, and we suspected that the timing of the burns would affect the abundance and size of galls relative to their overlap with the insects' lifecycle. There is also evidence of preference among galling insects for certain heights of S. altissima. We hypothesized that if the differing burn treatments resulted in varying heights of S. altissima, galls might become more prevalent in plots with their preferred average S. altissima height and basal stem width.