We have adapted an insect bioassay to test the insecticidal activity of lichen secondary products on Bemisia tabaciB type (syn. Bemisia argentifolii). Lichens are symbiotic organisms composed of a fungal partner, the mycobiont, in close association with one or more photosynthetic partners, the photobiont(s). The majority of lichen secondary metabolites originate from the mycobiont. Two metabolites that have previously been isolated and characterized were tested in the assay. (-)-Usnic acid, a triketone, is the key enzyme in the synthesis of porphyrins and chlorophylls and is an inhibitor of p-hydroxyphenyl dioxygenase (HPPD), an important enzyme in carotenoid biosynthesis. Vulpinc acid is an inhibitor in both respiratory and photosynthetic pathways. The bioassay employed scintillation vials containing disks of pumpkin leaves that were dipped into test solutions. Whiteflies were introduced into each assay vial and, after 48 hours, whitefly mortality was determined. Negative and positive controls were established with distilled water and Isotox©, a known pesticide of whiteflies. Both lichen secondary compounds showed effectiveness in limiting survival rates of whiteflies. Vulpinic acid, with an average mortality of 29%, had a slightly greater pesticidal activity than -(-)usnic acid, which caused an average of 24% mortality. We are continuing to screen additional lichen compounds and developing studies to determine the mode of action for the lichen secondary metabolites, at the biochemical and ultrastructural levels.
Species 1: Hemiptera Aleyrodidae Bemisia tabaci (sweetpotato whitefly, silverleaf whitefly)
Keywords: natural products, lichen secondary compounds
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA