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COSEWIC Assessment and Status Report on the Aweme Borer in Canada

Limiting Factors and Threats

The main limiting factor for Aweme Borers would be the amount and extent of the host plant(s). Nieminen (1996) has pointed out that the pattern of population extinction in moths is affected by host plant characteristics rather than by the characteristics of the moths themselves, and that monophagous moths (feeding on a single species or type of food) are more likely to suffer extirpation than are polyphagous species (feeding on two or more species or types of food), as are species that occur in highly fragmented disjunct populations.

According to Bird (1934), the single most important factor that contributes to the decline of the genus Papaipema is fire. The eggs, which are present from early fall through late spring, are exposed and are particularly vulnerable to fires. Controlled and other burns are known to have a negative impact on Papaipema species, in particular where fires consume all patches of the host plant in an area in a single season. Food plant patches may be unoccupied, or nearly so, by immature stages of Papaipema for the season following a fall, winter or spring burn because most individuals are killed (Schweitzer 1999). Almost all major workers on the genus have commented on the fire sensitivity of Papaipema eggs. Dana (1986) advises always assuming high mortality of Papaipema eggs in fall, winter or spring burn units. To preserve the rarer Papaipema populations, Schweitzer (1999) recommends protecting an adequate amount of the food plant by dividing occupied habitat into smaller burn units. These smaller units can be burned in rotation with 3-5 years between burns of a single unit, and adjacent units should not be burned in consecutive years. No Papaipema site should ever be entirely burned in a single year. The principle of burning blocks and/or rotating burns is applied and addressed in the prescribed burn plans for The Pinery Provincial Park.

As for most species of wildlife, loss of habitat, or some habitat element upon which the species is dependant, is probably the greatest threat. Loss or degradation of native habitats to agricultural, recreational or other uses is perhaps the most widespread and pervasive threat to most species of wildlife, including the Aweme Borer. Cottage and other recreational development has largely replaced native habitat in the Grand Bend – The Pinery Provincial Park region (K. Stead, pers. comm., 2004). Most of the park itself was, or has been, restored to native habitat and is now managed as nature reserve and natural environment zones. Overgrazing by deer and livestock can seriously affect native vegetation and the species dependant upon it. Massive overgrazing by “grossly out of control deer populations” was noted at The Pinery Provincial Park in 1993 (Schweitzer 1999). The deer herd is now being managed and the habitat has recovered measurably and continues to do so. Conversion of grassland habitats to forested habitats, either by natural succession speeded up by suppression of wildfires (i.e. Spruce Woods area) or by planting trees (i.e., historically in The Pinery Provincial Park), are possible threats to species dependant on open habitats. Stabilization of active dunes by vegetation, whether through natural processes or deliberate intervention, can also be a threat to species dependant on active dune habitats. Only patches of remnant bur-oak prairies remain on Manitoulin Island, and only those that have not been burned can be expected to possibly support the Aweme Borer (D. Lafontaine, pers. comm.). Most of the remnants are subject to forest ingrowth as a result of natural succession.

Pesticide applications, especially widespread applications of Lepidoptera-targeting agents, such as Btk spores, could pose a threat in areas where gypsy moths or other pest species are targeted for control.