The influence of natural enemies has led to the evolution of various predator avoidance strategies in herbivorous insects. Many caterpillars are exclusively active at night and rest during the day. It is widely assumed that nocturnal activity in caterpillars reduces their risk of falling prey to their natural enemies. To test this hypothesis, we compared predation pressure between day and night in tree-fall gaps and closed-canopy forest sites in an Amazonian primary lowland rainforest. Artificial clay caterpillars, showing camouflaged colouration (green), were exposed as potential prey to a natural predator community. Attacks were significantly more frequent during daytime and were reduced by about a quarter at night in tree-fall gaps, and by a third in closed-canopy forest sites. This supports the idea of time-dependent activity in caterpillars as an antipredatory adaptation. Further, independent of the time of day, predation pressure on caterpillars was significantly higher in tree-fall gaps compared to closed-canopy forest habitats. Nearly all predation events were caused by arthropods, whereas birds played a negligible role. Across both habitat types and time scales, ants acted as major predator group, emphasising their important role in population control of herbivorous insects in lowland rainforest ecosystems. This is the first experimental study using artificial caterpillars to examine whether timescheduling of exposition might influence predation risk amongst undefended, solitary, free-living lepidopteran larvae.

Research on canopy arthropods has progressed from species inventories to the study of their interactions and networks, enhancing our understanding of how hyper-diverse communities are maintained. Previous studies often focused on sampling individual tree species, individual trees or their parts. We argue that such selective sampling is not ideal when analyzing interaction network structure, and may lead to erroneous conclusions. We developed practical and reproducible sampling guidelines for the plot-based analysis of arthropod interaction networks in forest canopies. Our sampling protocol focused on insect herbivores (leaf-chewing insect larvae, miners and gallers) and non-flying invertebrate predators (spiders and ants). We quantitatively sampled the focal arthropods from felled trees, or from trees accessed by canopy cranes or cherry pickers in 53 0.1 ha forest plots in five biogeographic regions, comprising 6,280 trees in total. All three methods required a similar sampling effort and provided good foliage accessibility. Furthermore, we compared interaction networks derived from plot-based data to interaction networks derived from simulated non-plot-based data focusing either on common tree species or a representative selection of tree families. All types of non-plot-based data showed highly biased network structure towards higher connectance, higher web asymmetry, and higher nestedness temperature when compared with plot-based data. Furthermore, some types of non-plot-based data showed biased diversity of the associated herbivore species and specificity of their interactions. Plot-based sampling thus appears to be the most rigorous approach for reconstructing realistic, quantitative plant-arthropod interaction networks that are comparable across sites and regions. Studies of plant interactions have greatly benefited from a plot-based approach and we argue that studies of arthropod interactions would benefit in the same way. We conclude that plot-based studies on canopy arthropods would yield important insights into the processes of interaction network assembly and dynamics, which could be maximised via a coordinated network of plot-based study sites.

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