Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

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Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2Hyderabad, Andhra PradeshIndiaG. V. SubbaratnamAcharya N G Ranga Agricultural UniversityHyderabad, Andhra PradeshIndiaH. C. SharmaInternational Crop Research Institute for Semi-Arid TropicsHyderabad, Andhra PradeshIndiaGenerating Baseline Data for Insecticide Resistance Monitoring in Cotton Aphid, Aphis gossypii GloverABSTRACT The baseline susceptibility data weregenerated for the six commonly used insecticides viz.,thiamethoxam, imidacloprid, dimethoate, methyldemeton, acephate, and monocrotophos in cottonecosystems for the field population of Aphis gossypii.Populations were collected from the cotton fields of theDepartment of Cotton, Agricultural College andResearch Institute, TNAU, Coimbatore, India. IRACmethod No. 8 developed and recommended byInsecticide Resistance Action Committee (IRAC) witha slight modification was used for arriving the lethalconcentrations. The base line susceptibility data werecreated for seven generations. The LC50 values variedfrom 0.3412 to 1.0414 for thiamethoxam, 0.4583 to1.8055 for imidacloprid, 3.0096 to 10.6924 fordimethoate, 12.598 to 49.2606 for methyl demeton,1.4615 to 5.3284 for acephate, and 1.1866 to 3.7057for monocrotophos. The LC95 values varied from10.8617 to 35.2153 for thiamethoxam, 17.9171 to43.4310 for imidacloprid, 49.1667 to 629.6511 fordimethoate, 418.4538 to 1174.6270 for methyldemeton, 36.1800 to 130.4890 for acephate, and24.9571 to 139.4943 for monocrotophos.KEY WORDS: Insecticide resistance, Aphis gossypii,diagnostic dosesINTRODUCTION The importance of Aphis gossypiiGlover as a cotton pest is increasing throughout theworld (Leclant and Deguine, 1994). High aphidpopulations may stunt and retard cotton seedlinggrowth and development as a result of its feeding. Lateseason populations can cause decreased fiber quality asthe result of stickiness and the development of sootymould associated with honeydew dropped onto cottonfibers (Isely, 1946). There has been a general decline inthe effectiveness of several insecticides to control A.gossypii. The intensity of aphid infestations hasincreased over the last ten years and the use ofinsecticides to control aphids is questioned.The pest problem is aggravated more rapidly dueto control failures in many areas. Though controlfailure may be due to many factors, one of the majorfactors is the development of resistance to insecticides.The chief objective in resistance monitoring is toexaggerate the differences between susceptible andresistant individuals such that the frequency ofmisclassification is greatly reduced (Ffrench-constantand Roush, 1990). This is fulfilled by fixing thediagnostic doses.Resistance to A. gossypii is in the initial stages ofdevelopment and no systematic work has been done sofar on monitoring of insecticide resistance in India as ithas been done in Amrasca devastans (Distant) (JayaPradeepa and Regupathy, 2002), Helicoverpa armigera(Hub), Plutella xylostella (Linn.), and Spodopteralitura (Niranjan Kumar and Regupathy, 2001). Giventhe background, the present study was undertaken todetermine the diagnostic doses for the commonly usedinsecticides in cotton for A. gossypii.MATERIALS and METHODS The test insects werecollected from the cotton field, Department of Cotton,Agricultural College and Research Institute, TNAU,Coimbatore, India. The population was maintained forseven continuous generations without exposure topesticides under the laboratory conditions forgenerating the baseline data, i.e. fixing diagnosticdoses.The dilutions required were prepared from thecommercial formulations of insecticides using distilledwater. The dosages were attained after preliminaryrange finding studies for constructing logconcentration-probit-mortality(lcpm) lines (Regupathyand Dhamu, 2001).The wingless adults aphids of ca 1.45mm size andweighing ca 0.19mg were taken from the culturemaintained for the treatment. Each replicationconsisted of 10 aphids and there were threereplications. Bioassays were conducted following theprocedure based on the standard Bemesia tabaciGennadius susceptibility test, IRAC method No.8developed and recommended by the InsecticideResistance Action Committee, with slight modification.The experimental setup consisted of twodisposable cups, one as an inner test chamber and theother as an outer water reservoir. The cup that servedas the inner test chamber was taken and a hole waspierced in the centre of the bottom side of the cup.The young green uncontaminated leaves wereselected and the petiole was cut to a length ofapproximately four cm. The leaves were dipped in theconcentrations for five seconds holding the leaf by thepetiole with fine forceps. Care was taken to avoid thedamage to the petiole. Then the leaves were left for26
Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2drying in the open air by placing the leaves on the filterpaper (approximately five minutes). The petiole of theleaf was passed through the inner cup and the winglessaphids were released into the inner cup at the rate of 10aphids per cup and the cup was covered with muslincloth tightened with rubber band. A small amount ofwater was placed in a second cup and the test cup wasplaced inside that, so that it was supported by theprotruding petiole. Observations on mortality of aphidswere recorded after 48 h. The results were expressed aspercentage mortality.RESULTS and DISCUSSION The LC50 values varied from0.3412 to 1.0414 for thiamethoxam, 0.4583 to 1.8055for imidacloprid, 3.0096 to 10.6924 for dimethoate,12.598 to 49.2606 for methyl demeton, 1.4615 to5.3284 for acephate, and 1.1866 to 3.7057 formonocrotophos. Thiamethoxam was the most toxicpesticide. The acute toxicity of other insecticides basedon LC50 was in the order of imidacloprid >monocrotophos > acephate > dimethoate > methyldemeton for all the seven generations tested.The LC95 values varied from 10.8617 to 35.2153for thiamethoxam, 17.9171 to 43.4310 forimidacloprid, 49.1667 to 629.6511 for dimethoate,418.4538 to 1174.6270 for methyl demeton, 36.1800 to130.4890 for acephate, and 24.9571 to 139.4943 formonocrotophos. The acute toxicity was in the order ofthiamethoxam > imidacloprid > acephate >monocrotophos > dimethoate > methyl demeton for F1and F2 generations, and thiamethoxam > imidacloprid> monocrotophos > acephate > dimethoate > methyldemeton for rest of the generations tested.The susceptibility was gradually increased with thesucceeding generation, which is evident from thedecline in LC50 and LC95 values to all the insecticidestested. The extent of increase was greater for methyldemeton and dimethoate respectively. Thesusceptibility baseline data are not generated so far forthese insecticides taken up for the study. Hence, theLC95s of the insecticides were considered asdiscriminating doses for monitoring the fieldpopulations for their resistance to these insecticides.From the acute toxicity studies conducted in ourlaboratory, the discriminating doses (ppm) fixed were10 for thiamethoxam, 20 for imidacloprid, 50 fordimethoate, 400 for methyl demeton, 40 for acephate,and 20 for monocrotophos.Based on the slope function and increasedsusceptibility, the discriminating dose screen was fixedfor monitoring the level of insecticide resistance infuture.REFERENCESFfrench-constant, R.H. and R.T. Rousch. 1990. Resistance detection anddocumentation; the relative role of pesticidal and bio chemicalassays. In: Pesticide resistance in arthropods. (Eds.) R.J.Rousch andB.E.Tabashnik, Chapman and Hall; Newyork and London, pp 4-38.Isely, D. 1946. The cotton aphid. Arkansas Agric. Exp. Stn. Bull. 464.Jeya Pradeepa, S. and A. Regupathy. 2002. Generating baseline data forInsecticide Resistance Monitoring in cotton Leafhopper, Amrascadecastans (Distant). Resistant Pest Management Newsletter, 11(2).Leclant, F. and J.P. Deguine. 1994. Cotton aphids. In: Insect pests ofcotton. (Eds) G.A.Mathews and J.P.Tunstall. C.A.B.: 285353.Niranjankumar, B.V. and A. Regupathy. 2001. Status of insecticideresistance in tobacco caterpillar Spodoptera litura (Fabricius) inTamil Nadu. Pestic. Res. J. 13 (1): 86-89.Regupathy, A. and K.P.Dhamu. 2001. Statistics work book for InsecticideToxicology. Softech Computers, 206p.Praveen P. M. and A. RegupathyDepartment of Agricultural EntomologyAgricultural College and Research InstituteTamil Nadu Agricultural UniversityCoimbatore-641 003IndiaBaseline Susceptibility and Quantification of Resistance in Plutella xylostella (L.) to SpinosadABSTRACT Baseline susceptibility to spinosad in a P.xylostella population was determined by topicalbioassay. Significant variations in the LC50 valuesranged from 0.000250 in the 5th generation to0.000299 in the 1st generation. The resistance ratio forthe 7th generation as compared to the 1st generation27
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