Lethal and Sublethal Toxicities ofAnnona sylvatica(Magnoliales: Annonaceae) Extracts toZabrotes subfasciatus(Coleoptera: Chrysomelidae: Bruchinae)
Plant secondary metabolites comprise a diverse range of compounds (allelochemicals) that affect insect-plant interactions; many function in plant defense against herbivory. Thus, allelochemicals constitute an important source of insecticidal molecules that potentially can be used in different forms in integrated pest management programs. The objective of this study was to evaluate the bioactivity of ethanolic extracts and partially purified fractions of these extracts obtained from the leaves,
... d from the leaves, branches, and seeds of Annona sylvatica A. St.-Hil. (Magnoliales: Annonaceae), a native Brazilian species, against Zabrotes subfasciatus (Boheman) (Coleoptera: Chrysomelidae: Bruchinae). In the screening assay, the ethanolic extract of A. sylvatica seeds was the most promising treatment, causing lethal (LC 50 = 753.47 and 701.06 mg kg −1 for males and females, respectively) and sublethal effects, mainly oviposition deterrence (EC 50 = 438.70 mg kg -−1 ). On the other hand, ethanolic extracts prepared from branches and leaves caused only sublethal effects including mainly oviposition deterrence (EC 50 = 1,168.90 and 1,010.70 mg kg −1 , respectively) and reduction in number of offspring. Based on these results, the extracts were submitted to liquid-liquid partitioning, and their fractions were tested against Z. subfasciatus to verify their bioactivity. Overall, the results of the fraction bioassays showed evidence of synergistic interactions among compounds of different chemical classes and polarities. Chemical analyses of active fractions revealed the presence of triglycerides, alkaloids, and acetogenins in the seed fractions; alkaloids, lignans, and long-chain fatty acid ethyl esters in the branch fractions; and glycosides, flavonoids, terpenoids, and long-chain fatty acid ethyl esters in the leaf fractions. Thus, A. sylvatica is an interesting and potentially important source of structurally diverse grain-protective compounds.