title: Insecticidal activity of hypericin towardsManduca sexta larvae.
abstract: The toxic effect of hypericin (HYP), a photodynamic quinone that occurs in certain species of the genusHypericum, towardsManduca sexta third-instar larvae was investigated. The LD50 of purified hypericin was 16 μg/g larval initial fresh weight in constant light (22 W/m(2)). Reduced irradiance resulted in decreased mortality. Sublethal applications retarded larval growth (body fresh weight) in a dose-dependent manner. Toxicity had an absolute light dependence at the dose levels used, the active wavelengths being >500 nm. The phototoxic effect was rapidly lost when larvae were maintained in darkness (>8 hr) prior to irradiation. However, the potential for light-dependent mortality was retained if larvae were starved prior to irradiation.
authors.affiliation: School of Biological Sciences, University of Bath, BA2 7AY, Claverton Down, Bath Avon, UK.
authors.forename: R
authors.initials: R
authors.lastname: Samuels
authors.forename: P
authors.initials: P
authors.lastname: Knox