Arthropods in epiphytes: a diversity component that is not effectively sampled by canopy fogging

Insecticide fogging is often used to document arthropod species richness in forest canopies, but this technique may not effectively sample invertebrates that are concealed within a variety of microhabitats. We quantified the effects of fogging on invertebrates in canopy epiphyte mats of a Costa Rican cloud forest by extracting arthropods from 18 paired pre- and post-fogging samples. Mean abundance and morphospecies richness of living arthropods were respectively reduced by 33 and 30% in epiphyte material after fogging, but most organisms survived the treatment. Relative abundances of major taxa were unaffected by fogging. Herbivores were less abundant after fogging than other trophic groups, and the median body length of non-mite arthropods present in epiphytes was significantly smaller after fogging. Examination of seven post-fogging samples showed that many arthropods killed by insecticide remained trapped within the epiphyte material. These results provide the first quantitative assessment of a specific component of arboreal arthropod biodiversity that is missed by the fogging technique.