Fagodisuasión de extractos de Brugmansia candida (Solanaceae) en larvas de Hypsipyla grandella (Lepidoptera: pyralidae)

Abstract

Hypsipyla grandella is a key forest pest in Latin America and the Caribbean, where it has precluded attempts to establish commercial plantations of mahoganies (Swietenia spp.) and cedars (Cedrela spp.). In the search for methods to manage its larvae, being both preventative and cost-effective, as well as based upon resources from tropical flora, the crude flower extract of angel’s trumpet, Brugmansia candida, as well as four partitions thereof (water, hexane, dichlorometane, and ethyl acetate), were tested for phagodeterrence. Laboratory bioassays involved increasing concentrations of the crude extract (0.1, 0.3, 1.0, 3.2 and 10.0 % w/v) as well as each one of the partitions (in accordance to the yield obtained from the partitioning process). A randomized complete block design, with four replicates, was used. H. grandella instar III larvae were exposed for 24 h to Spanish cedar (Cedrela odorata) leaf discs dipped into the respective treatment, after which disc consumption was measured. Strong phagodeterrence was detected at concentrations as low as 1.0 % y 0.122 % w/v for the crude extract and the hexane partitions, respectively. In addition, a single bioassay was performed to compare a single concentration (0.38 % w/v) of the alkaloid scopolamine, which reduced consumption in 90 % with respect to the controls. Also, mortality and sublethal effects were assessed in larvae exposed to the crude extract, the hexane partition and scopolamine, with no evidence for them, which confirmed their phagodeterrence. Moreover, the crude extract was submitted to a phytochemical screening by means of a number of qualitative tests, which showed that alkaloids, tannins, triterpenes and cumarins were the most important secondary metabolites. Finally, the presence of scopolamine was confirmed in both the crude extract and the hexane partition, by means of the gas chromatography-spectrometry (GC-MS) analytical method. It is recommended to prepare a formulation of scopolamine plus some adjuvants, in order to test its effectiveness under greenhouse conditions, as a first step to advance in the development of a commercial phagodeterrent.