Defensive Mutualism of Endophytic Fungi: Effects of Sphaeropsidin A against a Model Lepidopteran Pest

Sphaeropsidin A (SphA) is a pimarane diterpene produced by several fungi associated with plants. Following previous evidence of insecticidal properties of SphA, we investigated its contact and oral toxicity against the model chewing lepidopteran Spodoptera littoralis. The compound showed no lethal effect when directly sprayed on larvae, while it produced an evident oral toxic effect, associated with sublethal effects. These results demonstrated that SphA might play a defensive role against lepidopteran insects in plants harboring the producing fungus, depending on the extent at which the endophytic strains are able to perform biosynthesis of this and eventually other bioactive metabolites in vivo.