Degree of Threat: High
Comments: Alien plants, inappropriate mowing, fires, trampling, grazing by wild and domestic mammals, and any other activity that incidentally kills immatures (less often adults) or damages their foodplants are among threats. If populations and habitats are as small as is now believed to be the case, even research and photography could pose threats in the form of trampling immature stages or damaging foodplants. Succession reduces habitats. Flooding during winter storms is considered a threat, although it cannot be assumed that such short term inundation of diapausing pupae, would necessarily be harmful. See Webster (1999) regarding a butterfly whose immature stages are routinely submerged during daily high tides nearly year round. Long term impacts of storm floods on the habitat need better documentation. Such storms might have some benefit by slowing succession. Btk applied against Asian gypsy moth is a potential threat if that pest is introduced again. However while it is sometimes assumed that Btk is lethal to all caterpillars, this is far from true (e.g. Peacock et al. 1998, among others). It is likely, but not actually known, that Btk would be lethal to at least the first instar or two, and maybe to all instars, if these were present at application time or a few days later. If sensitivity to Btk is identified as an important knowledge gap assays of larvae from a common subspecies of E. ausonides should address this gap. Recently (John Fleckenstein pers. com., October 2010, based on information from Ann Potter) reports a previously unrecognized threat. In the central valley of San Juan Island, winter plowing has resulted in large increases in weedy mustards upon which females oviposit. These are acting as ecological sinks drawing adults to lay eggs in plowed fields where larvae may do well (depending on insecticide use), but any resultant pupae are destroyed by subsequent plowing. The same is happening along the south coast of the island, where cereal grains are being raised. The extent of this effect at the population level needs to be evaluated.
