From fertilizer to insecticide: urban leaf litter chemistry alters the survival landscape of Aedes aegypti

BACKGROUND: Urban leaf litter accumulating in water-filled containers may function as either a resource or a stressor for Aedes aegypti larvae, yet the chemical and botanical drivers of these contrasting effects remain poorly understood. We combined untargeted metabolite profiling with factorial life-history bioassays to examine how leachates from two dominant street trees, Tipuana tipu and Handroanthus heptaphyllus, influence mosquito life story. First-instar larvae were exposed to 25%, 50% or 100% leachate aged 7 or 14 days. RESULTS: The T. tipu leachates were defined by persistent oxalic acid (cyclohexyl hexyl ester) and condensed tannins over 14 days of decay, whereas H. heptaphyllus rapidly lost most phenolics within the first week, shifting to profiles dominated by short-chain alkenes. At 25% dilution, T. tipu reduced mortality to 7% and produced adults with greater wing lengths than controls. However, mortality was >90% in the 50% and 100% T. tipu treatments, independent of leachate age. By contrast, H. heptaphyllus never produced mortality > 16% across all concentration-age combinations. Adult body size responded nonlinearly, with 100% T. tipu aged 14 days generated the smallest adults, whereas the largest adults emerged from 25% T. tipu. CONCLUSION: These results indicate that T. tipu can shift from a nutritional subsidy to a potent chemical stressor depending on concentration and aging, whereas H. heptaphyllus exerts consistently mild effects. Urban leaf litter therefore represents an overlooked but influential driver of mosquito performance in city environments.