SEASONALITY AND VERTICAL STRUCTURE OF LIGHT-ATTRACTED INSECT COMMUNITIES IN A DIPTEROCARP FOREST IN SARAWAK

Nocturnal flying insects were collected monthly for 13 months using ul tra violet light-traps set at various vertical levels in a weakly-seas onal, tropical lowland dipterocarp forest in Sarawak, Malaysia. Abunda nce, faunal composition, size distribution and guild structure of thes e samples were analyzed with respect to temporal and vertical distribu tions. The nocturnal flying insect community in the canopy level was h ighly dominated by fig wasps (84%) in individual number, and by scarab aeid beetles (28%) in weight. A principal component analysis on monthl y catches detected non-random, seasonal trends of insect abundance. Th e first two principal trends were an alternation of wetter (September to January) and less wet seasons (February to August) and an alternati on between the least wet (January to March) and the other seasons. Man y insect groups were less abundant in the least wet season than the ot her seasons, whilst inverse patterns were found in Scarabaeidae and Te nebrionidae. Significantly positive and negative correlations between monthly catch and rainfall were detected only in ovule-feeders and in phloem-feeders, respectively. Delayed, significant negative correlatio ns between monthly catch and 1-3 month preceding rainfall were more fr equently detected in phytophages, phloem-feeders, seed-feeders, wood-b orers and scavengers. The peak in abundance along vertical levels were found at the canopy level (35 m) for phloem-, ovule-, seed-, root-, f ungal-feeders and nectar collectors, at an upper subcanopy level (25 m ) for scavengers and aquatic predators, and at a middle subcanopy leve l (17 m) for ants. Catches at the emergent level (45 m) did not exceed those at the canopy level.