Spatial and temporal dynamics of Aroga moth (Lepidoptera: Gelechiidae) populations and damage to sagebrush in shrub steppe across varying elevation.

Abstract

Spatial and temporal variation in the density of the Aroga moth, Aroga websteri Clarke (Lepidoptera: Gelechiidae), and in its damage to its host plant, big sagebrush (Artemisia tridentata Nuttall), were examined at 38 sites across a shrub steppe landscape in mountain foothills of northern Utah. Sites were sampled from 2008 to 2012 during and after an outbreak of the moth, to assess whether and how local variation in moth abundance, survivorship, and damage to the host plant was accounted for by sagebrush cover, elevation, slope, aspect, or incident solar radiation. As moth numbers declined from a peak in 2009, individual sites had a consistent tendency in subsequent years to support more or fewer defoliator larvae. Local moth abundance was not correlated with sagebrush cover, which declined with elevation, and moth survivorship was highest at intermediate elevations (1,800-2,000 m). North-facing stands of sagebrush, characterized by lower values of incident solar radiation, were found to be especially suitable local habitats for the Aroga moth, as reflected in measures of both abundance and feeding damage. This high habitat suitability may result from favorable microclimate, both in its direct effects on the Aroga moth and in indirect effects through associated vegetative responses. North-facing sites also supported taller and more voluminous sagebrush plants in comparison to south-facing sites. Thus, the moth is reasonably predictable in the sites at which it is likely to occur in greatest numbers, and such sites may be those that in fact have most potential to recover from feeding damage.