Reproductive seasonality in the tropical butterfly Hypolimnas bolina (Lepidoptera : Nymphalidae) in northern Australia

Because seasonality in tropical environments is driven by variation in rain fall, phytophagous tropical organisms are expected to exhibit mechanisms of escape in space and time that allow them to synchronize their breeding eff orts with suitably wet periods of the year. This hypothesis was addressed b y studying the breeding phenology of the nymphalid butterfly Hypolimnas bol ina (L.) in the Australian wet-dry tropics. This species favours small, her baceous larval foodplants that either die off annually or exhibit marked de clines in leaf quality during the dry season. As expected, reproductive act ivity in H bolina was broadly correlated with both rainfall and humidity, w ith individuals spending part of the dry season (early April to late August ) sheltering in overwintering sites in a state of reproductive diapause. Th e timing of the overwintering period was similar between the 2 years, which suggests that individuals respond to seasonally predictable cues such as p hotoperiod. At least in 1998, the exit of butterflies from overwintering si tes was relatively sudden and coincided with the first spring rainfall even t. These findings suggest that H. bolina copes with seasonal adversity in t he tropics by means of a regularly timed diapause.