| Rice represents the basic food crop for the Third World’s population.Asia has more than half of world population,and more than 90 percent of world rice production is consumed only by Asia population.China occupies the first rank in the world rice production with an estimated production of 144,850,000 tons,which mainly associated with the national economy of the country.China expects to expand the current rice production by 20%more in 2030 due to the increase of the population.This seen to be a difficult task for the country that faces the menace of rice pests,rice diseases,and other abiotic factors.The planthoppers,brown planthopper(BPH)Nilaparvata lugens,white-back planthopper(WBPH)Sogatella furcifera and small brown planthopper(SBPH)Laodelph striatellus and green rice leafhopper(GRL)Nephotettix cincticeps,are rice sap-sucking insect pests as known by their devastating attack in several Asia temperate parts.They cause hopper burn,and others direct damages on rice crop by sucking from the phloem and transmitting plant viral diseases including the Rice Grassy Stunt Virus(RGSV)and Rice Ragged Stunt Virus(RRSV)to the rice plant.Leafhoppers and planthoppers in China are controlled generally by using various methods including chemical pesticides.Insect pests have been developed resistance to the conventional pesticide due to the long-term interaction of pesticides and insects.The non-selectivity of these insecticides against target pests and their persistence pose a risk of environmental contamination including the adverse effects to natural enemies in the ecosystem.In Integrated Pest Management(IPM),plant essential oils and its derived compounds are considered to be the perfect alternatives to conventional pesticides.This study aimed at a screening of nine chemical compounds from different essential oils against third instar nymphs of BPH and GRL using an H-tube olfactometer.Two effective chemical compounds selected from the screening assays,1-(2-hydroxy-4,6-dimethoxyphenyl)-Ethanone(Xanthoxyline)and(-)-caryophyllene-oxide,and their mixture(50:50)against female adults and third instar nymphs of the three species of planthoppers were investigated under laboratory and greenhouse conditions using the paired choice and no choice bioassays in detail.The mirid bug,Cyrtorhinus lividipennis,is an important natural enemy predating on planthopper and leafhopper in rice field.Thus,we evaluated the orientation(attractancy/repellency)of nymph and adults(males and females)C.lividipennis in response to xanthoxyline and(-)-caryophyllene-oxide under laboratory conditions.In the choice assay under laboratory conditions,in each pot,0.5 mL of component(10,100 and 1000ppm)was applied to one of the plants as treatment while the control plant in the pot was applied with 0.5 mL of solvent(Acetone+Tween 20(?)).In the no choice assays only one plant was planted the middle center of a pot,representing the treatment and another pot was for the control using the same concentrations and volumes as indicated in the choice assay.The data were recorded after 6,12 and 24h in both choice and no choice assays.The orientation assays of the C.lividipennis was evaluated by using the H-tube olfactometer.One cylinder contains the tested compound contained filter paper(10,100 and 1000ppm)and the other with solvent contained applied on filter paper as control.Both chemical compounds xanthoxyline and(-)-caryophyllene-oxide exhibited significant repellency against the three species of planthopper even if at 10 ppm.In a single test compound,xanthoxyline rate the highest repellency with maximum percent repellencies of 91.35±2.76%,88.41±2.33%and 83.10±1.97%for BPH,WBPH,and SBPH respectively at 1000ppm concentration.At the same time,xanthoxyline and(-)-caryophyllene-oxide did not affect significantly the orientation of the C.lividipennis.In the greenhouse,10 mL volume of compounds(10,100 and 1000ppm concentrations)and the mixture(50:50)was sprayed on one pot of plant in the cage as treatment pot,and the same volume of solvent was applied on the other pot as control plant.Xanthoxyline and(-)-caryophyllene-oxide repelled female adults and nymphs of the three species of planthopper.The highest percent repellencies to each planthopper were recorded by xanthoxyline present repellencies of 74.78±2.50%,75.35±3.15%and 53.17±4.46%respectively for BPH,WBPH,and SBPH at 1000ppm concentration.The leafhoppers’ preliminary results indicated repellency from four compounds xanthoxyline,piperitone,citral,and alpha-terpineol at 100ppm concentration.Citral rated the highest repellency while(-)-caryophyllene-oxide rated the lowest,respectively with 56.82±11.46%and 9.64±9.68%after 12h.For planthoppers,this present study demonstrates the potential effect of two chemical compounds,xanthoxyline and(-)-caryophyllene-oxide,and their mixture at equal portion to repel the three planthoppers of N.lugens,S.furcifera and L.striatellus.As there is no orientation effect on C.lividipenis from these two compounds,it removes the doubt about their adverse effects on the natural enemy.In future,it is necessary to evaluate the acute or chronic toxicity of these two compounds to N.lugens S.furcifera and L striatellus.Field studies of these compounds also need to be evaluated for more confirmations of our results.Also,the possibility of mixing the planthoppers’ repellents and the leafhopper’s repellents together for widely control rice’s pest reminds us could be carrying out the mixture experiment in future.These results may contribute to the Integrated Pest Management program for the development of green insecticides. |
