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en . Res., 4 1 ) : 6 0- 62 1 990)Relative toxicity of some important insecticidesto Bihar hairy caterpillar, Spilosoma obliqua Walker) Arctiidae : Lepidoptera)

D.K. NAGIA, S NJ Y KUM R AND M.L. S INICentral Insecticides Laboratory, Directorate Plant Protection.Quarantine and Storage. NH-W. Faridabad-121 001 IndiaABSTRACf : The toxicity of eleven Insecticides to second Instar larvae of Spitosoma

obliqruz W1k.) was studied.On the basis of L values, th e descending order of toxicity was: deltamethrln 0.00313) followed by cypermethrln 0.00601),fenpropat hrln 0.00921), fenvalerate 0.00952), ftuvallnate 0.01556), endosulfan 0.01914), methyl parathion 0.02057), andmooocrotophos 0.02786). Dlazlnon, trlazophos and ac:ephate were found Ineffective.

Bihar hairy caterpillar, Spilosoma obliqua Wlk.) is apestofnumber of important crops,viz vegetables cabbage, radish, cauliflower, bean, potato), pulses pigeon pea, cowpea, greengt llOl, black gram, soybean), oilseeds castor, mustard,sunflower, groundnut, sesamum), fibrescotton,jute),and medicinalplantsHibiscusabelmoschusLinn.,H. rosa-s{nensis LinnMenthaarvensisLinn., Chenopodium ambrosioides Linn.). Its early instars lst/2nd)feed gregariouslyand late instars 3rd/4th) scatter in the field. Earlier about threedozen insecticides were evaluatedliy various workers against this pest. Some of these like deltamethrin, cypermethrin, quinalphos,endosulfan, fenvalerate, permethrin, methyl parathion, trichlorphon and phosphamidon provedto be effective Prasad and Sachan, 1985; Singh; Sircar and Dhingra, 1985; Nagia, Kumarand Saini, 1990). Some workers reported that early larval instars of the pest were moresusceptible to insecticides and easy to control in comparison to late instars Yadav, Singh andSinha, 1984; Saini, 1986). Larvae of Bihar hairy t ~ r p i l l r are also harmful in its ~ stages lst/2nd instar larvae).Hence, the relative toxicity of some of the insecticides found effectiveagainst grown-up larvae of this insect, along with dew newer insecticides was evaluated againstt 2nd instar larvae.

MATERIALS AND METHODSCulture of Bihar hairy caterpillar, S. obliqua was maintained in the laboratory on castorRicinuscommunisL.) leaves at26 1C and 70 5 relativehumidity RH)in the environmentchamber. Second instar larvae were used for evaluating efficacy of deltamethrin 2.8 EC,cypermethrin 10 Ee fenpropathrin 10 EC, fenvalerate 20 EC, fluvalinate 25 EC, endosulfan35 EC, methyl parathion 50 EC, monocrotophos 36 SL,diazinon 20 EC, triazophos 40 ECand acephate 75 SP in the laboratory after dissolving them in distilled water for requisiteconcentrations.Castor.leaves were cut to 90 mm diameter size and placed inside t Petri dishes 100 15 mm) keeping ventral surfa,ce of the leaves upwards. Five different concentrationsof each test insecticide were sprayed over such leaf portions under Potter s spray tower using

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Relative toxicity of insecticides to S. o liqu (Walker) 611ml spray solution. One leaf portion served as one replicate and three such replications wereincluded in each experiment. Sprayed leaves were dried for about 10 minutes under ceilingfan and placed over moist tissue paper to keep them turgid in the fresh Petri dishes 145 x20 mm). Ten second instar larvae were then released over these leaves in each Petri dish.Control treatmentwas sprayedwith wateronly. Such Petridisheswith treated leaves and larvaewere kept in the environment chamber maintained at 26 lC and 70 5 RH. The dataon mortality of larvae were recorded 48 hours after their exposure. on treated leaves. Also,the moribund insects were considered as dead. The data were subjected to probitanalysis tocalculate and .LC90 values of different insecticides (Finney, 1971).

RESULTS AND DIS USSIONAll the five synthetic pyrethroids were comparatively more toxic to early stage larvaethan organochlorine and organophosphate insecticides included in the experiment. LC and

LC 90 values of deltamethrin, cypermethrin, fenpropathrin, fenvalerate and fluvalinate werecalculated as 0.00313 and 0.01043, 0.00601 and 0.03100, 0.00921 and 0.04636, 0.00952 and0.02062, and 0.01556 and 0.09350 per cent. respectively. The similar values for endosulfan,methyl parathion and monocrotophos were 0.01914 and 0.16220, 0.02057 and 0.44495, and0.02786 and 0.11600 per cent, respectively. These values for diazinon, triazophos and acephatecould not be calculated sincemaximum 3.33 to 30 per cent insect mortality was obtained withas high as 0.1 per cent concentration of these insecticides (Table 1). .Table 1. Toxicity of eleven insecticides against early stage larvae of S. o liqu (Wlk.)

Insecticide Regression equationDeltamethrin Y = 1.3376 2.4490x 0.00313Cypermethrin Y =3.6003 1.7968x 0.00601Fenpropathrin Y = 3.2411 + 1.8239x 0.00921Fenvalerate Y = 1.2706 3.8114x 0.00952Auvalinate Y = 3.0404 + 1.6438x 0.01556Endosulfan Y = 3.2319 1.3792x 0.01914Methyl parathion Y = 3.7408 + 0.9588x 0.02057Monocrotophos Y = 2.0148 2.0660x 0.02786Diazinon 0.1 concentration gave 30.00 larval mortalityTriazophos 0:1 concentration gave 2333 larval mortalityAcephate 0.1 concentration gave 3.33 larval mortality

0.010430.031000.046360.020620.093500.162200.444950.11600

In each case, data were found to be significantly homogeneous at P = 0.05, Y Probit kill x logconcentration, LC ll=Concentration calculated to give 50 mortality, LCl =Concentration calculatedto give 90 mortality. .

Amongst syntheticpyrethroids, deltamethrinwas almosttwiceas toxic as cypermethrin,thrice as fenpropathrin and fenvalerate, and five times as toxic as fluvalinate at LC level.When relative toxicity of all the insecticides tested was compared among themselves withLC sovalue ofmonocrotophos, the leasteffectiveinsecticideasunity,deltamethrin, cypermethrin,

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62 D.K N GI SANJAY KUMAR AND M.L. S INIfenpropathrin fenvalerate fluvalinate, endosulfan and methyl parathion were 8.9 4.64 3.022.93 1.19 1.46 and 1.35 times as toxic as monocrotophos Table 2). The toxicity trend ofinsecticides was however slightly different at LCgQ level.Table 2. Relative toxicity of insecticides amongst themselves at LC level against S. obliqua Wlk.)Insecticide Relative toxicity based on

DELT CYP FENP FENV FLUV ENDO MP MONODeltamethrin 1.00. 1.92 2.94 3.04 4.97 6.12 6.57 8.90Cypermethrin 0.52 1.00 1.53 1.58 2.59 3.18 3.42 4.64Fenpropathrin 0.34 0.65 1.00 1.03 1.69 2.08 j 3.02Fenvalerate 0.33 0.63 0.97 1.00 . 1.63 2.01 2.16 2.93Fluvalinate 0.20 0.39 0.59 0.61 1.00 1.23 1.32 1.79Endosulfan 0.16 0.31 0.48 0.50 0.81 1.00 1.07 1.46Methyl parathion 0.15 0.29 0.45 0.46 0.76 0.93 1.00 1.35Monocrotophos 0.11 0.22 0.33 0.34 0.56 0.69 0.74 1.00

Thus deltamethrin was most toxic insecticide against early instar larvae of S. obliquawhile cypermethrin fenpropathrin fenvalerate and fluvalinate were more effective thanendosulfan methyl parathion and monocrotophos. Diazinon triazophos and acephate werepractically ineffective insecticides.

REFERENCESFinney, D 1 1971. Probit Analysis Cambridge University Press, London. 333 pp.Nagia, D. K., Sanjay Kumar and Saini, M L 1990. Laboratory evaluation of some insecticides against

Bihar hairy caterpillar, Spilosoma obliquaWalker) Arctiidlie: Lepidoptera) on castor Ricinuscommunis L Pl. Prot. Bull. India , 42 1 2) : 13-16.Prasad, M. S R K and Sachan, G. C 1985. Toxicity of some synthetic pyrethroids by three methods

of application against Diacrisia obliqua Walker. Pesticides 19. 12) : 50-53.Saini,M. L 1986. Use of pesticides in the integrated pestmanagementtechnology. Pl. Prot. Bull. India ,38 : -4) : 83-86.Singh, D. S., Sircar, P and Dhingra, S. 1985. Status ofBihar hairy caterpillar,Diacrisia obliquaWalker

Arctiidae: Lepidoptera) inthecontext ofsusceptibility to pyrethroidandnon-pyrethroidinsecticidesevaluated during the last two decades. ene. Res 9 1) : 15-18.Yadav,R P., Singh,R. andSinha, P.K. 1984. Stomach and contact toxicity ofsomeimportant insecticides

to Bihar hairy caterpillar, Diacrisia obliquaWalker infesting sweetpotato, Ipomoea batatasPoir. ene. Res 8 1) : 42-45.

Accepted: May 10, 1990)