Background: Aedes aegypti is the primary vector of viruses, such as Zika, chikungunya, yellow fever, and dengue. In this context, a biomonitored chemical study was conducted to evaluate the activity of the crude extract of the endophytic fungus Phomopsis sp. against the larvae of Aedes aegypti.Methods: Crude extract, fractions, and isolated substances were evaluated in in-vitro assays against third-stage larvae of Aedes aegypti. Results:We isolated 3-nitropropionic acid with an LC 50 of 15.172 ppm and LC 90 of 18.178 ppm after 24 hours of larval exposure. Conclusions:The results indicated that 3-nitropropionic acid exerted larvicidal activity.