Behaviour of late-instar gypsy moth larvae in high and low density populations

1. Using scaffolding and night‐vision equipment, we observed fifth and sixth instars of the gypsy moth, Lymantria dispar (L.), on Quercus velutina Lam. in the field. 2. In low‐density populations, larvae fed at night and spent the day resting in sheltered sites away from the canopy. In high‐density populations, larvae remained in the canopy throughout the day and night, and the amount of feeding during daylight hours increased with population density. 3. Larvae at all population densities used a similar sequence of behaviours and sampled a number of leaves when selecting feeding sites, but larvae in high‐density populations switched feeding sites more frequently and fed continuously for shorter periods. 4. Larvae seldom interfered with each other's feeding in any of the populations. 5. When fifth instars were collected from the field and held for 24 h in an electronic feeding monitor, they maintained feeding rhythms that were characteristic of their source populations. Larvae spent more time crawling and less time feeding when offered foliage from high‐density rather than low‐density populations.