Two field experiments determined an effective intertrap distance (ITD) for early detection and delimitation sparse gypsy moth (Lepidoptera: Lymantriidae, Lymantria dispar L.) populations in mountainous terrain. This study found that current Animal and Plant Health Inspection Service trapping guidelines are not sufficient for early detection of small gypsy moth populations in mountainous terrain. Detection trapping in mountainous terrain should have an ITD of not more than 804 m. Delimiting trapping should use a grid design with an ITD of 152 m. A related study determined natural adult male mortality in the climate of the intermountain West, which includes Utah, Nevada, western Wyoming, and southern Idaho. An interaction was found between mortality, temperature, and humidity. During high temperatures, most mortality occurred on the second day. When lower temperatures prevailed, the largest percent mortality occurred on the third or fourth day.