The chemical diversity of essential oils from galls of two Artemisia spp., and their insecticidal activity against the storage pest Callosobruchus chinensis

Plant galls are an important chemical resource, and allow scientists to explore the active substances resulting from continuous interactions between plants and gall-inducing insects. In this study, the gall-inducing insect, Cryptosiphum atriplicivorum (Hemiptera: Aphididae), was identified for the first time from galls on Artemisia sieversiana and A. sylvatica. The chemical components of the galls were analyzed using hydro-distillation, and higher concentrations of essential oils (EOs) were found in galls on A. sylvatica than in those from A. sylvatica. GC-MS analysis revealed that the major chemical components in the EOs from A. sieversiana and A. sylvatica galls were monoterpenoids and sesquiterpenoids, including eucalyptol, (–)-borneol, (+)-camphor, β-caryophyllene, and (E)-β-farnesene. Concentrations of these chemicals were higher in the galls than in uninfected plants. Fumigant toxicity assays demonstrated that A. sylvatica and A. sieversiana gall EOs had strong insecticidal activity against C. chinensis, with LC50 values of 7.65 ± 1.84 and 46.79 ± 5.21 μL/L, respectively. Moreover, the monoterpenoids eucalyptol, (–)-borneol, and (+)-camphor, which were prominent in the gall tissues, all exhibited significant fumigant activity against Callosobruchus chinensis (Coleoptera: Bruchidae), with LC50 values of 20.96 ± 4.19 μL/L, 7.37 ± 0.60 μL/L, and 4.89 ± 1.52 μL/L, respectively. Interestingly, fumigation with these EOs at insecticidal concentrations did not affect soybean seed germination or seedling growth. These results illustrate that chemicals from the galls on A. sieversiana and A. sylvatica have the potential to be exploited as insecticides for overcoming storage pests.