UCLA

Many montane, pine-dominated forests in the western United States are home to the Pandora moth, Coloradia pandora, a large lepidopteran species that has a 2-year life cycle, generally alternating between “moth years” and “larval years.” During the latter, larvae descend from their feeding locations in the pine canopy, disperse across the ground, and burrow in the soil for pupation. This study examines the nature of larval movement on trees as well as on and in the ground; the time required for the various phases during the day of descent; and parasitoid and environmental threats during ground dispersal. Locomotion during descent from trees was relatively slow at 0.64 cm/s (range 0.44–0.93 cm/s). Larvae slowed further as they transitioned from tree boles to the ground and were initially unsteady. Once on the ground, larvae quickly recovered and were able to move significantly faster (1.63 cm/s, range 1.23–2.08 cm/s) than during descent from the boles. About 10% of dispersing larvae were attacked by ovipositing tachinid flies and larvipositing sarcophagid flies. Larvae being attacked by parasitoids or traveling in full sun at high temperatures increased their speed to the point that locomotion appeared poorly coordinated. This apparently stressful locomotion was often followed by the affected animals burrowing only a centimeter below the surface of the loose soil, duff, and pine needles. Shallow burrowing by larvae stressed by heat or parasitoid attack may result in a positive feedback in terms of vulnerability because the resulting pupae would in turn be more exposed to several additional threats. Moreover, a warming climate would likely exacerbate a number of these linked causes of larval and pupal mortality.