Repellency of essential oils against Nephotettix cincticeps: Laboratory and glasshouse assays

Four oils from Piper nigrum, Litsea cubeba, Zanthoxylum bungeanum and Curcuma longa were obtained by ethanol extraction. The repellency of these oils and two major compounds (linalool and piperine) was evaluated against female adult and third-instar nymphs of the rice pest, Nephotettix cincticeps, under laboratory and glasshouse conditions. Paired-choice and no-choice assays were used for each treatment, with essential oils evaluated after 24 and 48hr of exposure and chemical compounds evaluated after 12 and 24hr of exposure. The potential effects of essential oils on activities of glutathione S tranferase (GST), carboxyl esterase (CarE) and acetyl cholinesterase (AchE) were also evaluated after 48hr of exposure to leafhoppers. The constituents of the essential oils were determined using GC-MS. The results showed that the major components in the oils were piperine (34.75%) for P.nigrum, 9,12-octadecadienoic acid (Z,Z) (18.74%) for L.cubeba, ethanone, 1-(2-hydroxy-4,6-dimethoxyphenyl) (18.51%) for Z.bungeanum and turmerone (15.89%) for C.longa. In all cases, the essential oils repelled female adults and third-instar nymphs of N.cincticeps. The repellency of the tested oils and chemicals compounds in the paired-choice assay was higher than in the no-choice assay. In all experimental conditions, P.nigrum and C. longa oils were the most and the least potent, respectively. Linalool was the best repellent among the single-tested compounds under laboratory conditions. In the glasshouse study, the highest repellency was observed in the mixture of linalool and piperine. GST and CarE activities of leafhoppers were significantly enhanced by exposure to the four essentials oils; AchE activity increased significantly only in the P.nigrum and L.cubeba assays. Our results clearly indicate that the tested oils and chemical compounds are promising agents for developing plant-based pesticides to control N.cincticeps.