The Influence Of Pesticides On Rice Plant Volatiles And Its Ecological Effects

The influence of pesticides on rice plant volatiles and its ecological effects were investigated in a system involving pesticides, rice, pests (brown planthopper (BPH), Nilaparvata lugens St?l and the rice leaf folder (RLF), Cnaphalocrocis medinalis Guenee) and their natural enemies (an egg parasitoid, Anagrus nilaparvatae Pang et Wang, a predatory bug, Cyrtorhinus lividipennis Reuter and a predatory spider, Pirata subpiraticus Boes.et str.). The results are as follows:1) Volatiles of rice plants treated with 4 pesticides, including imidacloprid (new neonicotinoid insecticide), azadirachtin (botanical insecticide), triazophos (organophosphorus insecticide), MCPA-Na (hormone herbicide), were collected by solid phase microextraction (SPME) and then identified by gas chromatography coupled with mass spectrometry (GC-MS). Forty components were collected from headspace of rice plants infested by BPH under imidacloprid application, 25 of which were identified, including terpenes (16 kinds), alcohols (3 kinds), alkanes (3 kinds), ketones (1 kind), acetates (1 kind) and naphthalene (1 kind); Twenty-five components were collected from headspace of rice plants infested by BPH under azadirachtin application, 14 of which were identified, including terpenes (8 kinds), alcohols (3 kinds), alkanes (2 kinds) and acetates (1 kind); Thirty-six components were collected from headspace of rice plants infested by RLF under triazophos application, 15 of which were identified, including terpenes (8 kinds), alcohols (3 kinds), alkanes (2 kinds), acetates (1 kind) and ketones (1 kind); Twenty-four components were collected from headspace of healthy rice plants under MCPA-Na application, 8 of which were identified, including terpenes (6 kinds), alcohols (1 kind) and alkanes (1 kind). Eleven of the identified components were newly found in rice plants, including (-)-isoledene,(-)-α-cedrene,(+)-β-cedrene,thujopsene,cadina-1(10),4-diene,cadina-3,9-diene,2,4a,5,6,7,8,9,9 a-octahydro- 3,5,5-trimethyl-9-methylene-1H-benzocycloheptene,cedrene,muurolene,1,2,3,4,6,8 a-hexahydro-1-methylethyl-4,7-dimethyl-naphthalene and 2,6,10-trimethyl-tetradecane.Both kinds and proportions (percent of total peak area) of the sesquiterpenes were the highest in all treatments (pesticides treated or not). Compared with the CK (water treated plants), the treatments of pesticides did not result in the emission of new compounds, but rather the relative proportions among the compounds in the blend were altered. The proportions of 20% components had significant differences under imidacloprid application at three levels. The proportions of 85% components changed at different days after imidacloprid treatment. Furthermore, the proportions of 90% components were significantly changed due to the interactions between imidacloprid and other factors. The corresponding values of azadirachtin were 88.0%,76.0%,96.0%, triazophos were 13.9%,75.0%,88.9% and MCPA-Na were 54.2%,45.8%,75%, respectively. Therefore, the effect of pesticide on rice volatiles (ordered from high to low) were azadirachtin > imidacloprid > triazophos > MCPA-Na. The botanical insecticide azadirachtin was most effective which maybe have relation with its action mode. Among the changed components, methyl salicylate, (-)-isoledene, (-)-α-copaene, (-)-α-cedrene, (+)-β-cedrene, (-)-isocaryophyllene, (-)-zingiberene, cedrol, n-heptadecane were much easier to be influenced by pesticides treatment. The various biosynthesis pathways were responsible for the different changing trends of volatile components.2) Orientation responses of A. nilaparvatae (using Y-tube olfactometer) and C. lividipennis (using H-tube olfactometer) to rice plants treated by imidaclopid were conducted. The results showed that volatiles emitted from rice plants treated by imidacloprid with 3 concentrations had significant effects on the orientation responses of A. nilaparvatae and C. lividipennis. When the density of BPH was 10 females per plant, a majority of the parasitoid were attracted to rice plants treated with low concentration (15.00 g a.i /hm2) of imidacloprid, but not to high concentration (37.50 g a.i / hm2) ones, except at 5 days after treatment (DAT). The attractions of rice plants to the bug were water treated ones (CK) > low concentration treated ones > high concentration treated ones. Volatiles emitted from rice plants at different days after imidacloprid treatment also had significant effects on host searching behaviors of A. nilaparvatae and C. lividipennis. When BPH density was 2 females per plant, the parasitoid exhibited greater preference to rice plant volatiles from 1DAT, 3DAT, 5DAT than those from 7 DAT. When the damage density was 10 females per plant, the parasitoid preferred rice plant volatiles from 3 DAT under high imidacloprid application than those from 1 DAT. The bug preferred volatiles emitted from rice plants at 1DAT than those from 3DAT, 5DAT, 7DAT. The effects (attraction or repellent) of the components changed after imidacloprid treatment, such as methyl salicylate, (-)-isoledene, (-)-α-copaene, (-)-zingiberene, n-heptadecane, thujopsene, n-hexadecane, on the natural enemies maybe one reason of their orientation responses.3) Orientation responses of A. nilaparvatae and P. subpiraticus to rice plants treated by azadirachtin at three levels were studied with Y-tube olfactometer. The results indicated that when the BPH density was 2 females per plant, volatiles emitted from rice plants treated by azadirachtin with different concentrations had no effect on the orientation behaviors of the natural enemies. Only when the BPH density was 10 females per plant, host searching behaviors of natural enemies had significant differences. The parasitoid oriented significantly towards the odours emitted from rice plants under high (2.25 L/hm2) azadirachtin application at 1 DAT compared with water treated ones (CK). When compared with rice plants under high azadirachtin application, the parasitoid preferred volatiles from low (1.13 L/hm2) azadirachtin treated ones at 1 DAT and 3 DAT. The behavioral responses of P. subpiraticus to rice plants under azadirachtin application had no significant difference except at 3 DAT between high azadirachtin application plants and the CK plants. The rice plants under azadirachtin application were more attractive to the natural enemies than CK plants, which indicated that the botanical insecticide azadirachtin was safe to natural enemies and was helpful to improve their natural control effect on the pests. And thus, the mediations of pesticide applications should be taken to make full use of the synergism of pesticide and plant volatiles in sustainable management of rice pests.4) The biological activities of 14 rice volatile components to 3 natural enemies of BPH were measured in Y-tube olfactometer or H-tube olfactometer. The results demonstrated that under specific concentrations of volatile compounds and hours after releasing insects, the bug could be obviously attracted by linalool, methyl salicylate, (-)-isoledene, (-)-isocaryophyllene and repelled by linalool, nerolidol, cedrol. The spider could be attracted by methyl salicylate, (-)-isocaryophyllene, trans-β-farnesene, nerolidol, and repelled by (-)-α-copaene, n-hexadecane and cedrol. The wasps were attracted by (-)-isoledene and repelled by limonene. methyl salicylate, (-)-isocaryophyllene and cedrol had the same effects on behavioral responses of the bug and the spider, and limonene, (-)-isoledene were common active components of the bug and the parasitoid, while there was no common active compound between the spider and the parasitoid. Among the 14 compounds tested, (-)-α-cedrene, (+)-β-cedrene, (-)-zingiberene and n-heptadecane had no biological activity to all 3 natural enemies. The volatile components that attractting the natural enemies could be used in field to enhance the control of the natural enemies to the pests.5) The biological activities of 14 rice volatile components to BPH were studied. H-tube olfactory test showed that under specific concentrations of volatile compounds and hours after releasing insects, BPH could be obviously attracted by limonene, (-)-isoledene, (-)-isocaryophyllene, trans-β- farnesene and cedrol, and repelled by linalool, methyl salicylate, (-)-α-copaene, (-)-α-cedrene, (+)-β-cedrene, (-)-isocaryophyllene, trans-β-farnesene and nerolidol. The issue needing attention was (-)-isocaryophyllene and trans-β-farnesene had opposite influence to BPH at different concentrations. (-)-zingiberene, n-hexadecane and n-heptadecane showed no biological activity to BPH. In electrophysiological responses test, most of the sesquiterpenes (except trans-β-farnesene and (-)-zingiberene) elicited strong responses, and monoterpenoids and terpene oxides elicited moderate responses, while alkanes elicited the lowest or no responses. The EAG responses of BPH to (-)-isoledene, (-)-isocaryophyllene and (-)-α-copaene were the highest, and (-)-zingiberene, n-heptadecane were the lowest, which were almost consistent with the behavioral responses. The results suggested that volatiles from rice plants after pesticide treatment played a vital role in their host-finding behavior, however, each component played on different role.