Compounds from Duguetia lanceolata St.- Hil. (Annonaceae) bioactive against Zabrotes subfasciatus (Boheman) (Coleoptera: Chrysomelidae: Bruchinae)

The variety of chemical compounds produced by members of Annonaceae exhibiting wide activity against pest organisms makes this family an interesting source for insecticidal compound identification. Accordingly, this study first aimed to evaluate the lethal and sublethal effects of ethanolic extracts of different parts of Duguetia lanceolata St.-Hil. against Zabrotes subfasciatus (Boheman) (Coleoptera: Chrysomelidae: Bruchinae), the primary pest of stored beans in tropical regions. Based on a screening bioassay, the ethanolic extract from D. lanceolata leaves was selected for chemical partitioning due to its high bioactivity against the weevil. The hexanic partition of the ethanolic leaf extract caused 98% mortality of Z. subfasciatus adults in a residual contact bioassay and completely eliminated the number of eggs per sample. Chromatography subfraction Flh2-5, a hexanic partition of D. lanceolata leaves, resulted in 100% mortality of Z. subfasciatus adults. An aromatic compound (2,4,5-trimethoxystyrene) and a mixture of sterols [(campesterol (8.44%) + stigmasterol (12.37%) + sitosterol (79.19%)] were isolated from subfraction Flh2-5 using various chromatographic procedures. The aromatic compound resulted in 60% weevil mortality, and the steroid mixture applied at 75 mg kg−1 promoted 28% mortality; in contrast, the positive control (K-Obiol® 2P, deltamethrin 2 g a.i./kg) at 375 mg kg−1 resulted in 100% mortality. Moreover, both 2,4,5-trimethoxystyrene and K-Obiol® 2P completely prevented oviposition on bean samples, demonstrating that, similar to a deltamethrin-based formulation, 2,4,5-trimethoxystyrene is able to act as a grain protector. Therefore, the aromatic compound and mixture of isolated sterols from D. lanceolata may be suitable management tools of stored-product pests and promising sources of insecticidal molecules with both lethal and sublethal effects on Z. subfasciatus.