Diel activity of arboreal arthropods associated with Papua New Guinean trees

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Abstract
The diel activity of arboreal arthropods foraging within the crowns of nine species of trees native to submontane rain forests in Papua New Guinea was studied. Data were collected over a 30-day period, using modified flight-interception traps, which are described briefly. Sampling was designed to enable segregation of material into day- and night-catches. Arthropod activity (measured by the number of individuals collected) was correlated positively with minimum air temperature. As a probable consequence, overall arthropod activity was significantly higher during day-time than night-time and night catches represented 72% of day catches. Predators, parasitoids, wood-eaters, ant workers and entomophagous arthropods were significantly more active during day than night. Few arthropod groups showed an inverse behaviour. Regression slopes comparing entomophages versus herbivores during day- and night-time were not significantly different. The data do not support the hypothesis that herbivores are particularly active during night-time in rain forests in order to escape day-active predators. However, this hypothesis may apply in specific situations, which are reviewed briefly. Additional hypotheses explaining the relatively low densities of insect herbivores in tropical rain forests but a level of leaf damage comparable to that estimated for their counterparts in temperate forests are suggested.