Sap-sucking insects (Auchenorrhyncha, Hemiptera) were sampled quantitatively from the foliage of 15 species of Ficus (Moraceae) in a lowland rain forest in Papua New Guinea. Continuous sampling throughout 12 months produced 61,777 individuals and 491 species. Two seasonality parameters, circular statistics and Lloyd's index, were calculated for 139 species with a sample size of more than 36 individuals. Most of the species were present in the adult stage for at least half of the year, and many of them continuously throughout the year. However, almost all species exhibited marked seasonal changes in abundance. The abundance peaks of species were scattered throughout most of the year, but more species reached their population maximum during the wet, especially early wet, season than during the dry season. Overall species richness and abundance of Auchenorrhyncha were also higher during the wet than the dry season. A significant correlation between seasonality and host specificity was revealed in the auchenorrhynchan community. In particular, species evenly distributed throughout the year had a tendency to feed on a larger number of Ficus species than seasonally more restricted species. The seasonality, and the seasonality versus specificity correlation, were independent of species abundance. Among the most abundant species (n > 300) there was a marginally significant negative correlation between abundance and host specificity, so that polyphagous species had, on average, larger populations than specialists. There was no similar correlation among rarer species. The Auchenorrhyncha comprises three feeding guilds, which were also analysed separately. The mesophyll-feeding guild exhibited more pronounced seasonality than the phloem- and xylem-feeders. This difference could be explained as a part of the overall correlation between seasonality and host specificity as mesophyll-feeders were significantly more host specific than the other two guilds.
Keywords: Host specificity; Insect abundance; Key words Herbivores; Phenology; Species diversity.