Insect assemblages attacking seeds and fruits in a rainforest in Thailand

Abstract

Abstract Insect seed predators are important agents of mortality for tropical trees, but little is known about the impact of these herbivores in rainforests. During 3 years at Khao Chong (KHC) in southern Thailand we reared 17,555 insects from 343.2 kg or 39,252 seeds/fruits representing 357 liana and tree species. A commented list of the 243 insect species identified is provided, with details about their host plants. We observed the following. (i) Approximately 43% of identified species can be considered pests. Most were seed eaters, particularly on dry fruits. (ii) Approximately 19% of parasitoid species (all Opiinae) for which we could determine whether their primary insect host was a pest or not (all Bactrocera spp. breeding in fruits) can be considered beneficials. (iii) The seeds/fruits of approximately 28% of the plant species in this forest were free of attack. Phyllanthaceae, Rubiaceae and Meliaceae were attacked relatively infrequently; in contrast, Annonaceae, Fabaceae, Sapindaceae and Myristicaceae were more heavily attacked. There was no apparent effect of plant phylogeny on rates of attack but heavily attacked tree species had larger basal area in the KHC plot than rarely attacked tree species. (iv) Insects reared from fleshy fruits were more likely to show relatively stable populations compared to insects reared from dry fruits, but this was not true of insects reared from dipterocarps, which appeared to have relatively stable populations throughout the study period. We tentatively conclude that insects feeding on seeds and fruits have little effect on observed levels of host abundance in this forest.