Evaluation of Natural Products as Antifeedants for the Pales Weevil (Coleoptera: Curculionidae) and as Fungitoxins for Leptographium procerum

Four natural plant compounds (limonin, S (+) and R (−) carvone, and cucurbitacin) and one insect pheromone (verbenone) were evaluated for antifeedant activity against the pales weevil, Hylobius pales (Herbst), on Pinus strobus seedlings and for toxic activity against the pathogenic fungus, Leptographium procerum (Kendrick) Wingfield, which is vectored by H. pales to P. strobus. All compounds demonstrated significant antifeedant activity in a choice test on treated pine seedlings, but none completely eliminated feeding. Only cucurbitacin elicited a linear dose-response relationship, with significant activity occurring at concentrations as low as 0.10 μg/ml. The other compounds significantly reduced feeding at concentrations as low as 1 μg/ml (the lowest concentration at which they were tested). Total feeding activity was unaffected for all but one treatment (S (+) carvone at 1 μg/ml) when compared with feeding on the untreated control seedlings. It is, therefore, unlikely that the compounds in this study were toxic to the weevils during the 2 d evaluation period. In the fungitoxin test, all compounds except cucurbitacin suppressed germination of L. procerum spores. R (−) carvone was the most effective, allowing only 5% germination at 1 μg/ml, compared to 96% germination in the water solvent.