Abstract. 1. Seasonal or annual population fluctuations have been reported for various tropical insect species, exhibiting one or more peaks in abundance at certain times of the year. Such fluctuations have mostly been observed in areas that experience annual wet and dry seasons, and not in areas where climatic fluctuations are unpredictable on an annual basis.
2. This study attempted to evaluate the extent of seasonality in population fluctuations of a light-trapped chrysomelid assemblage consisting of 25 Garelucinae and one Eumolpinae in a Bornean rainforest that is characterised by an aseasonal climate.
3. This study also attempted to test the effects of short-term rainfall changes and leaf-flushing phenology on chrysomelid population fluctuations.
4. The majority of the chrysomelid species showed one or more abundance peaks that were unrelated to season.
5. The population fluctuations did not correspond to short-term fluctuations in rainfall or leaf-flushing phenology, although these environmental factors somewhat correlated with each other and fluctuated irregularly.
6. These results suggest that populations of most chrysomelids fluctuate aseasonally and that short-term fluctuations in rainfall and leaf-flushing phenology hardly affect population fluctuations in Bornean rainforests where seasonal climate patterns are weak.