Are Prescribed Fires Endangering the Endangered Silphium Borer Moth (Papaipema silphii)?

Abstract

The silphium borer moth (Papaipema silphii), a rare endemic insect in midwestern prairies, completes one life cycle per year and has a short dispersal distance. The moth eggs are presumably laid in the duff near host Silphium plants. Silphium species distributions are primarily restricted to fragmented prairie patches, commonly in upland habitats that can burn more intensely than lowland patches. Thus, these moths must cope with existence in a fire-prone environment. Currently, there is controversy regarding how prescribed fire affects the sustainability of prairie invertebrate populations. We counted larval densities of silphium borer moths within thirty-four 0.1-ha plots in three isolated southern Wisconsin prairies with different burn patterns. The median density of larvae was significantly lower in the rotationally burned prairie than in one of the prairies that has been repeatedly burned edge-to-edge. Larval densities did not differ significantly between recently burned and recently unburned plots. These findings suggest that prescribed fires are not endangering the silphium borer moth, regardless of burn method, at least at these three sites. However, more studies at more locations are needed. We still recommend burning only two-thirds of isolated prairies every year.