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Title: Acute toxicity of plant essential oils to scarab larvae (Coleoptera: Scarabaeidae) and their analysis by gas chromatography-mass spectrometry

Author
item Ranger, Christopher
item Reding, Michael - Mike
item OLIVER, JASON - Tennessee State University
item Moyseenko, James
item YOUSSEF, NADEER - Tennessee State University
item Krause, Charles

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2012
Publication Date: 2/1/2013
Citation: Ranger, C.M., Reding, M.E., Oliver, J., Moyseenko, J.J., Youssef, N., Krause, C.R. 2013. Acute toxicity of plant essential oils to scarab larvae (Coleoptera: Scarabaeidae) and their analysis by gas chromatography-mass spectrometry. Journal of Economic Entomology. 106(1):159-167.

Interpretive Summary: Larvae of scarab beetles (Coleoptera: Scarabaeidae), also known as white grubs, are important contaminant and root-herbivore pests of ornamental crops. In order to develop alternatives to conventional insecticides, 24 plant essential oils were tested for their toxicity to larvae of the Japanese beetle, European chafer, oriental beetle, and northern masked chafer. Essential oil solutions were applied to the larvae, and mortality was assessed 1 day after treatment. A wide range in acute toxicity was observed across all four species of scarab larvae. Of the 24 oils tested, allyl isothiocyanate, cinnamon leaf, clove, garlic, and red thyme oils exhibited toxicity to all four species of white grubs. Allyl isothiocyanate was the most toxic oil tested against the European chafer, and among the most toxic against the Japanese beetle, oriental beetle, and northern masked chafer. Red thyme was also comparatively toxic to the Japanese beetle, oriental beetle, European chafer, and northern masked chafer. In general, the oriental beetle was most susceptible to the plant essential oils and the northern masked chafer was the least susceptible. Analysis of the active oils by gas chromatography-mass spectrometry revealed a diverse array of compounds. These results will aid in identifying active oils and their constituents for optimizing the development of plant essential oil mixtures against scarab white grubs.

Technical Abstract: Larvae of scarab beetles (Coleoptera: Scarabaeidae) are important contaminant and root-herbivore pests of ornamental crops. In order to develop alternatives to conventional insecticides, 24 plant essential oils were tested for their acute toxicity against third instar larvae of the Japanese beetle Popillia japonica Newman, European chafer Rhizotrogus majalis (Razoumowsky), oriental beetle Anomala orientalis (Waterhouse), and northern masked chafer Cyclocephala borealis Arrow. Diluted solutions were topically applied to the thorax, which allowed for calculating LC50 and LC90 values associated with 1 d after treatment. A wide range in acute toxicity was observed across all four species of scarab larvae. Of the 24 oils tested, allyl isothiocyanate, cinnamon leaf, clove, garlic, and red thyme oils exhibited measurable toxicity to all four species. Allyl isothiocyanate was the most toxic oil tested against the oriental beetle, European chafer, and northern masked chafer, and among the most toxic against the Japanese beetle. Red thyme was also comparatively toxic to the Japanese beetle, oriental beetle, European chafer, and northern masked chafer. Interspecific variability in susceptibility to the essential oils was documented, with 12, 11, 8, and 6 of the 24 essential oils being toxic to the oriental beetle, Japanese beetle, European chafer, and northern masked chafer, respectively. Analysis of the active oils by gas chromatography-mass spectrometry revealed a diverse array of compounds, mostly consisting of mono- and sesquiterpenes. These results will aid in identifying active oils and their constituents for optimizing the development of plant essential oil mixtures against scarab larvae.