Field trials were conducted in Thailand to determine the effect of Thai neem seed oil, monocrotophos (Azodrin), and carbosulfan (Posse) on rice yields (Oryza sativa L., variety RD7). Neem-treated plots did not yield significantly more rice than control plots. Plots treated with monocrotophos or carbosulfan had significantly higher yields than control plots or neem-treated plots. The rice yields were correlated with the levels of three insect species: Nephotettix virescens (Distant) (Homoptera: Cicadellidae), Nilaparvata lugens (Stal) (Homoptera: Delphacidae), and Chilo sp. (Lepidoptera: Pyralidae). Only N. virescens exceeded its economic threshold. More than 95% of the variation in yield data could be explained by the N. virescens levels 36 days after transplanting, N. virescens populations were reduced by applications of monocrotophos and carbosulfan. N. virescens was not effectively controlled by neem seed oil. N. virescens control with monocrotophos or carbosulfan at economic threshold appears to significantly increase rice yields

Jahn, Gary C.

Proceedings of the Hawaiian Entomological Society

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Vol. 31, December 31,1992 125Effect of Neem Oil, Monocrotophos, andCarbosulfan on Green Leafhoppers,Nephotettix virescens (Distant)(Homoptera: Gicadellidae) andRice Yields in Thailand1GARYC.JAHN2ABSTRACT. Field trials were conducted in Thailand to determine the effect of Thai neemseed oil, monocrotophos (Azodrin), and carbosulfan (Posse) on rice yields (Oryza saliva L.,variety RD7). Neem-treated plots did not yield significantly more rice than control plots. Plotstreated with monocrotophos or carbosulfan had significantly higher yields than control plotsor neem-treated plots.The rice yields were correlated with the levels of three insect species: Nephoteltix virescens(Distant) (Homoptera: Cicadcllidac), Nilaparvala lugens (Slal) (Homoptera: Delphacidae),and Ckilo sp. (Lcpidoptcra: Pyralidae). Only N. virescens exceeded its economic threshold.More than 95% of the variation in yield data could be explained by the N. virescens levels 36days after transplanting. A', virescens populations were reduced by applications ofmonocrotophos and carbosulfan. N. virescens was not effectively controlled by neem seed oil.N. virescens control with monocrotophos or carbosulfan at economic threshold appears tosignificantly increase rice yields.KEYWORDS: Neem, rice yield, Nepholettix virescens, monocrotophos, carhosulfan.Extracts of the Thai neem tree, Azadirachta indica van siamensis Valetonhave been reported to disrupt the normal feeding behavior ofseveral insectspecies (Sombatsiri and Tigvattanont 1983). Neem oil, produced at thevillage level in developing countries, can supposedly reduce dependenceon imported synthetic insecticides and supplement income (Ahmed andGrainge 1985, 1986). As a Peace Corps Volunteer aiding economic development in rural Thailand, I assessed the potential ofThai neem oil for ricepest control.One objective of my study was to determine the effect of two syntheticinsecticides and crude Thai neem oil on grain yield and on three rice pestspecies: the green leafhopper (GLH) Nephotettix virescens (Distant)(Homoptera: Cicadellidae), the brown planthopper (BPH) Nilaparvatalugens (Stal) (Homoptera: Delphacidae), and the rice stem borer (STB)Ckilo sp. (Lepidoptera: Pyralidae). The other objective was to assess theeffect of these rice pests on grain yield. Pest surveillance systems are basedon the assumption that the yield of a crop can be increased by taking action■Journal Series No. 3672 ofthe Hawaii Institute ofTropical Agriculture and Human Resources.'Department of Entomology, University of Hawaii at Manoa, Honolulu, Hawaii 96822.TABLE 1. Mean number of Nephotettix vimcens per sweep per 25 m2 plot center in Amphur Sribrajan, Suphanburi, Thailand*.Population of green leafhoppers at DATTreatmentAzodrinPosseLow Thai NeemMedium Thai NeemHigh Thai NeemControlRate0.3 liter Al/ha0.3 liter Al/ha15 kg/ha35 kg/ha50 kg/ha10.6a0.7a0.7a1.0a1.2a0.6a50.1a0.1a0.1a0.1a0.2a0.2a160.3a0.7a1.1a0.8a0.8a0.8a190.1a0.8a0.5a0.8a0.5a0.5a321.2b4.7ab6.4ab3.8a4.6ab9.3a362.8b3.9b10.6a7.4ab10.4a11.6a471.1a1.4a1.6a1.7a2.1a2.1a♦Means within a column followed by the same letter are not significantly different at the 5% level by Duncan's Multiple Range Test (ANOVA).days after transplanting. Treatments were applied 2, 17, 33 and 48 DAT.500.9a0.9a0.9a0,8a0.6a1.0aDAT = Proc1Q.IDHawaii)inEntomo og calSocietyVol. 31, December 31,1992 127against a pest at the economic threshold. The Thai Department of Agricultural Extension and the Thai-German Plant Protection Programme promote pest surveillance as a means ofdetermining when to take pest controlaction.This paper describes the results of the first experiment to evaluate theefTectiveness of Thai neem oil for rice pest control under field conditions.MATERIALS AND METHODSIn Amphur Sribrajan, Suphanburi, Thailand on 7 April 1986 twenty-five-day-old seedlings of rice variety RD7 were transplanted lo 10 X 10 m plotswith 3 seedlings per hill at 25 X 25 cm spacing (i.e. 270,000 plants perhectare). Treatments in this experiment consisted of monocrotophos(Azodrin), carbosulfan (Posse), and three different concentrations ofThaineem oil. Controls were sprayed with water containing 1.25 cc sticker/spreader per liter of water, the same amount of sticker/spreader used ineach of the treatments. Each treatment was replicated 3 times and arrangedin a randomized complete block design. Plots were 1 m apart and blockswere 5 m apart. The areas between plots and between blocks were plantedwith rice and left untreated.TABLE 2. Grain yield of rice RD7 in different N. vinscrns control treatments in AmphurSribrajan, Suphanburi, Thailand*.TreatmentAzodrinPosselx>w Thai NeemMedium Thai NeemHigh Thai NeemControlRate0.3 liter Al/ha0.3 liter Al/ha15 kg/ha35 kg/ha50 kg/haMean yieldin kg/25 m' plot15.5b15.3b6.7a9.4a8.5a6.4a% Moisture16.9a17.5a16.9a17.4a17.1a16.9a'Means within a column fallowed by the same letter are not significantly different at the 5%level by Duncan's Multiple Range Test. (ANOVA).Neem seeds were collected in February 1986 in Suphanburi. Neem oilwas produced by as inexpensive a method as possible, so that the technologymight be easily transferred to Thai rice farmers. Neem seeds were dried inthe shade on burlap, because azadirachtin, one of the antifeedanttriterpenoids in neem oil, decreases in antifeeding potency when exposedto sunlight (Stokes and Redfern 1982). Seeds were then ground with ahand-powered coffee grinder. Ground seeds were stored in coffee tins untilneeded. Crushed seeds were soaked in a solution of 1.25 cc sticker/spreader per liter ofwater in the following ratios: 0.03 kg/liter, 0.07 kg/liter,and 0.10 kg/liter. After 12 to 24 hours the mixture was filtered throughcheese cloth. The solid residue was discarded, and the remaining solutionapplied to the field immediately after stirring.128 Proceedings, Hawaiian Entomological SocietyTABLE 3. Percent yield gain of rice RD7 and area under curve of N. viirscens populationsfor each treatmentTreatmentAzodrinPosseLow Thai NeemMedium Thai NccmHigh Thai NeemControlRate0.3 liter Al/ha0.3 liter Al/ha15 kg/ha35 kg/ha50 kg/ha% Yield gain142.19139.064.6946.8832.810.00Area undercurve4649381581.5146616031930.5TABLE 4. Determination coefficient (r2), probability level, and treatment regression values between yield gain and area under population curves of Nepholettix vinscms(GLH), Nilaparvata lugens (BPH), and Chilosp. (STB) in rice RD7.PestGLHBPHSTBH.8906.2000.2925Prob. Level.00466.93256.26786Slope-0.1-0.318.4Intercept212.076.0-9.2Both of the synthetic insecticides were applied at 0.3 liters of activeingredient per hectare; a concentration consistent with the manufacturer'srecommendations. Thai neem oil, monocrotophos, and carbosulfan wereapplied at approximately 5 liters of solution per plot with a hand pumpsprayer.Plots were treated 2,17,33, and 48 days after transplanting (d.a.t.). Eachplot was surveyed for GLH, BPH, and STB the day before and 2 to 3 daysafter each treatment application. GLH population densities were estimatedwith sweep net collections. Ten sweeps were made in the 5- by 5-m centerof each plot. BPH and STB densities were estimated by directly countingtheir numbers on every other hill along one diagonal of the 5- by 5-m centerof each plot Ten hills were surveyed per plot.Yield data were collected from the 25 m2 center of each plot. Grainmoisture was determined with the air-oven method of Xuan and Ross(1972). Analysis of variance (ANOVA) with Duncan's multiple range test(P = 0.05) was used to detect differences in yield due to treatment effect(Sokal and Rohlf, 1981).The average number of each species surveyed was calculated for everysurvey date, according treatment. Regression analyses were performed onthe area under the insect population curve (AUIPC) for each species foreach treatment, versus the yield gain for each treatment. Yield gain wascomputed as a percentage using the formula %G = (T-C)/C, where T isthe average yield for a treatment, and C is the average yield for the untreated control plots. If the AUIPC for a species versus yield gain had a highr2 value and was significant (P < 0.05), then the effect of that species (forVol. 31, December 31,1992 129each survey day) on yield was measured using regression analysis {Teng andBissonnette 1985). Differences in insect density due to treatment (withineach survey day) were detected by ANOVA with Duncan's multiple rangetest (P = 0.05).RESULTSThroughout the experiment, the number ofGLH in neem-treated plotsand control plots did not differ significantly. At 32 d.a.t. monocrotophos-treated plots had significantly less GLH than control plots. At 36 d.a.t.monocrotophos and carbosulfan had significantly less GLH than controlplots (Table 1).Plots treated with Thai neem oil did not produce significantly more ricethan control plots (Table 2). Monocrotophos-and carbosulfan-treated plotshad yields significantly higher than the control plots (Table 2). There wasa yield gain of 149.19% in monocrotophos plots, and of 139.06% in carbosulfan plots (Table 3). Percent yield gain caused by pest suppression canbe satisfactorily explained by the regression model for AUIPC ofGLH. BPHor STB levels could not explain the differences in yield (Table 4). The GLHpopulation 36 d.a.t. explained more than 95% of the variation in the yielddata (Table 5).TABLZ 5. Determination coefficient (r*), probability level, and regression values betweenyield gain and N. vharens population levels according to treatment on differentDAT in rice RD7*.DAT15161932364750r*.0663.2892.6190.0257.5475.9547.6564.0072Prob. Level.62231.27108.06335.76147.09268.00078.05062.87305Slope-52.6-668.0-195.0-39.8-15.7-16.8- 132.139.5Intercept104.8150.0207.282.2152.8191.9281.227.4•DAT = Days After Transplanting.DISCUSSIONBPH and STB were not numerous and apparently had no effect on theyield. Neither species reached its economic threshold established by theInternational Rice Research Institute (IRRI) (Reissig et al., 1986). Therefore, in this field trial, BPH and STB did not achieve pest status.Monocrotophos and carbosulfan treatments each reduced the densityof GLH and, apparently as a result, increased the grain yield. When theeconomic threshold of two GLH/sweep is reached, IRRI recommends130 Proceedings, Hawaiian Entomological Societyspraying a systemic insecticide (Reissig et al., 1986). This recommendationis consistent with the data. The first treatment application after the GLHexceeded the economic threshold was 33 d.a.t. (Table 1). This applicationmost likely caused the reduction in GLH in the monocrotophos and car-bosulfan plots that was observed 36 d.a.t. Since GLH levels 36 d.a.t. explained more than 95% of the variation in yield data (Table 5), it was theapplication 33 d.a.t. that probably resulted in the increased yields in plotstreated with synthetic insecticides.Contrary to my expectations when I began this investigation, there wasno evidence that applications of crude Thai neem seed oil improved yieldor controlled pests in rice. Based on the results of this experiment, Thairice farmers should continue using monocrotophos or carbosulfan to control GLH in rice when the pest reaches the economic threshold.In Thailand, as in many developing nations, the majority of poisoningcases are of farmers exposed to pesticides (Kritalugsana 1988). This problem results from the improper use of these chemicals. Industrialized nationsuse 80% of the world's agrochemicals, yet only 1% of the human deathsdue to acute pesticide poisoning are in those same countries (Jeyaratnam,1988). Vorley (1988) makes the point that the insecticides which farmersalready prefer must be incorporated into IPM systems until inexpensive,selective insecticides are developed. If synthetic insecticides are used prudently, they can be an important part of an IPM system (Soekarna, 1988).Developing effective, safer insecticides is a laudable long term goal. Inthe meantime, educating farmers in the proper application, storage, anddisposal of insecticides is the most important way to reduce the incidenceof pesticide poisoning.ACKNOWLEDGEMENTSMy thanks to the staff of die Suphanburi Plant Protection Subunit forassistance in the field, to S. Dokmaihom and S. Chantarasa-ard for technicaladvice, to P.S. Teng for reviewing the statistical analysis, and to R.F.L. Mauand N.J. Reimer for helpful criticism of the manuscript. Financial supportfor this study was provided by the Peace Corps and the Thai Departmentof Agricultural Extension.REFERENCES CITEDAhmed, S. and M. Grainge. 1985. The use of indigenous plant resources in rural development:potential of the nccm tree. InLj. Dev. Tech. 3:123-130.Ahmed, S. and M. Grainge. 1986. Potential of the neem tree (Azadirachta indica) Tor pestcontrol and rural development. Economic Botany, 40:201-209.Jeyaratnam, J. 1988. Pesticide poisoning: improving and evaluating pesticide data collectionin Southeast Asia. In Pesticide Management and Integrated Pest Management in Southeast Asia (eds. P.S. Teng and K.L Heong) pp. 325-330. College Park: Consortium forInternational Crop Protection.Kritalugsana, S. 1988. Pesticide poisoning studies and data collection in Thailand. In PesticideManagement and Integrated Pest Management in Southeast Asia (eds. P.S. Teng andK.L. Heong) pp. 321-324. College Park: Consortium for International Crop Protection.Vol. 31, December 31,1992 131Reissig, W.H., EA. Heinrichs, JA. Litsinger, K. Moody, L. Fiedler, T.W. Mew, and A.T. Barrion.1986. Illustrated Guide to Integrated Pest Management in Rice in Tropical Asia. International Rice Research Institute, Manila, Philippines, 411 pp.Soekarna, D. 1988. The role of insecticides in rice IPM systems. In Pesticide Management andIntegrated Pest Management in Southeast Asia (eds. P.S. Teng and K.L. Heong) pp.67-72. College Park: Consortium for International Crop Protection.Sokal, R.R. and F.J. Rohlf. 1981. Biometry, 2nd edition. W.H. Freeman and Company, SanFrancisco, U.S.A., 859 pp.SombaUiri, K. and S. TigvattanonL 1983. Effects of neem extracts on some pests of economicimportance in Thailand. Proceedings of the 2nd International Neem Conference, pp.95-100.Stokes, J.B. and R.E. Redfern. 1982. Effect of sunlight on azadirachtin: antifeeding potency.Journal of Environmental Science and Health A17(l):57-65.Teng, P.S. and H.L. Bissonnette. 1985. Developing equations to estimate potato yield losscaused by early blight in Minnesota. American PotatoJournal 62:607-fil8.Vorley, W.T. 1988. IPM in rice — an extension role for the agrochemical industry. In PesticideManagement and Integrated Pest Management in Southeast Asia (eds. P.S. Teng andK.I- Heong) pp. 215-220. College Park: Consortium for International Crop Protection.Xuan, V. and V.E. Ross. 1972. Training Manual for Rice Production. The International RiceResearch Institute, Manila, Philippines, 141 pp.132 Proceedings, Hawaiian Entomological Society

Effect of Neem Oil, Monocrotophos, and Carbosulfan on Green Leafhoppers, Nephotettix virescens (Distant) (Homoptera: Cicadellidae) and Rice Yields in Thailand

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Effect of Neem Oil, Monocrotophos, and Carbosulfan on Green Leafhoppers, Nephotettix virescens (Distant) (Homoptera: Cicadellidae) and Rice Yields in Thailand

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