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Variation in the Susceptibility and Resistance of Spodoptera litura (Fab) (Delhi and Punjab Populations) to Various Synthetic Pyrethroids
M.H.Kodandaram
and Swaran Dhingra
Division of Entomology,
Indian Agricultural Research Institute
New Delhi-110012,
India
ABSTRACT The third instar larvae of S. litura obtained from Punjab was 20.74, 15.46, 12.9, 9.59 and 7.05 and 16.74, 13.22, 21.18, 11.50 and 4.83-fold resistance to deltamethrin, alphacypermethrin, cypermethrin, betacyfluthrin and fenvalerate, respectively, when applied by direct spray and leaf dip method, respectively as compared to Delhi population. Regardless of method of application betacyfluthrin was most effective against Delhi and Punjab population.
KEY WORDS Spodoptera litura, Susceptibility, Relative Resistance and Synthetic Pyrethroids
INTRODUCTION Spodoptera litura (Fab), the tobacco caterpillar earlier known to be a sporadic pest has emerged as major polyphagus pest in recent past. This pest is reported to attack a wide range of vegetables, cash and fiber crops. Because of their ability to inflict serious economic damage to these crops, the pest has been subjected to heavy dose of insecticide treatments. Typical field control of this pest includes use of several synthetic pyrethroids, organophosphates and carbamates. Amongst different group of insecticides, synthetic pyerthroids constitute 8-75 % and are widely used allover India to control this pest. Cypermethrin is most commonly used followed by fenvalrate, deltamethrin, lambdacyhalothrin and betacyfluthrin. Due to indiscriminate and non-judicious use of these insecticides has resulted in the development of high degree of resistance to these compounds. The level of resistance to synthetic pyrethroids vary/differ significantly and constitute a serious threat to crop production in many regions1-7. Thus, to know the level of susceptibility and resistance of field collected populations of third instar larvae of S. litura from Delhi and Punjab, to synthetic pyrethroids, the present investigation was carried out a series of dosage mortality studies to provide base line data and any change in ld-p lines for several synthetic pyrethroids between the two populations by direct and spray and leaf dip method.
MATERIALS AND METHODS The larvae of S. litura were collected from the fields of Indian Agricultural Research Institute, New Delhi and Phagwara district. of Punjab were reared in laboratory on castor leaves at 27±1º C and 60±5 % RH under laboratory conditions. The insecticides viz., Betacyfluthrin (Bayer India Ltd), Alphamethrin (BASF India Ltd.), Cypermethrin (Zeneca ICI Agrochemicals), Deltametnrin (Aventis crop science Ltd.) and Fenvalerate (Rallis India Ltd.) evaluated in the present studies were obtained as commercially available formulations from their respective source of supply. Different concentrations of various insecticides were prepared by using distilled water for the dilution of emulsifiable concentrates (EC). Direct Spray: Ten third instar larvae (7 day old) of S. litura were randomly selected and placed in the petri-dishes and one ml of each concentration of the test emulsions was directly sprayed at a pressure of 340 g cm-2 under Potter's tower. In case of control the larvae were sprayed with distilled water. The sprayed petri-dishes containing treated larvae were air dried for about 5 minutes and then transferred to separate glass jars (15 X 10 cm) containing fresh untreated castor leaves as food. Leaf Dip: The larvae of S.litura were exposed to insecticide residue on castor leaves. Leaf discs of approximately 6cm diameter were cut from the castor leaves and were dipped in the required concentrations of different insecticides for 20 seconds and then air-dried. The treated leaf discs were then transferred to clean jars (15 X 10 cm) and ten third instar larvae were released in each jar. For control the leaf disc was dipped in the sterile water. In both the bioassay operations the jars were covered with muslin cloth and kept in laboratory at 27±1º C and 60±5% RH. There were 3 replications for each concentration and untreated control. Mortality was recorded 24 h after treatment. The moribund insects were counted as dead. The data so obtained was subjected to probit analysis8. The relative susceptibility of various insecticides was found out by calculating the LC50 of cypermethrin as unity. The relative resistance was calculated as LC50 of Punjab population / LC50 of Delhi population.
RESULTS AND DISSCUSSION The results presented in table 1 indicate that betacyfluthrin was most effective against third instar larvae of both the population of S. litura by direct spray. The LC50 values of betacyflutrin, alphamethrin, delatmethrin, cypermethrin and fenvelrate were 0.00054, 0.00519, 0.0071, 0.0159 and 0.0368 to Delhi population and 0.00518, 0.08028, 0.1473, 0.2056 and 0.2597 to Punjab population, respectively.
Response S. litura to five pyrethroids by leaf dip method shows (Table 2) that Delhi population was 37.50, 4.45, 1.04, and 0.26 and Punjab population was 17.57, 0.56, 0.33, and 0.29 times more susceptible to betacyfluthrin, alphamethrin, deltamerthrin and fenvelrate as compared to cypermethrin respectively. Regardless of method of application both the population of S. litura were highly susceptible to betacyflutrin.
Comparison of LC50 values for synthetic pyrethroids viz., betacyflutrin, alphamethrin, delatmethrin, cypermethrin and fenvelrate of Delhi and Punjab population of S. litura indicated differential shift in the level of resistance. It is evident from the data (Table 3). that the third instar of S. litura obtained from Punjab showed 20.74, 15.46, 12.93, 9.59 and 7.05-folds resistance to deltamethrin, alphacypermethrin, cypermethrin, betacyfluthrin and fenvalerate, respectively, when compared to Delhi population. Based on the LC90 values obtained, the order to relative resistance was cypermethrin (34.67) > alphacypermethrin (28.28) > deltamethrin (20.86) > betacyfluthrin (3.24) > fenvalerate (1.78)
The relative resistance values based on LC50 of the Punjab population when compared to that of Delhi was 21.18 fold to cypermethrin, 16.74 to deltamethrin, 13.22 to alphacypermethrin, 11.50 to betacyfluthrin and 4.83 to fenvalerate, when evaluated by leaf-dip method. The change in the order of relative resistance remained unaltered even at LC90 level (Table 4). But there was change in the order to resistance as compared to direct spray method, the order was cypermethrin > deltamethrin > alphacypermethrin > betacyfluthrin > fenvalerate.
Armes et al4 reported resistance levels between 0.2 to 197 and 8 to 121 fold to cypermethrin and fenvelrate respectively in S .litura starins collected from Andhra Pradesh. While studying the variation in the efficacy of synthetic pyrethroids against susceptible (Delhi) and resistant (Guntur) level population of S. litura, Rao and Dhingra5 reported similar results. According to them, Guntur population of S. litura were 4 and 5 fold resistance to cypermethrin and fenvalerate respectively, when compared with Delhi population. Recently Kranthi et al.6 detected high levels of resistance to cypermethrin ranging from 67 to 148 in the strains of S. litura collected from both north and south India.
Thus, it is evident from the investigations that the third instar larvae of S. litura obtained from Punjab were resistant to all the five synthetic pyrethroids. The LC50 values obtained would serve as ready reckoner for the selection of insecticides for field strains. Also, such base line data could be used as critical inputs in deployment of synthetic pyrethroids and insecticide resistance management programmes.
REFERENCES
1. Ramakrishnan, N., Saxena, V.S. and Dhingra, S. 1984. Insecticide resistance to the population of Spodoptera litura (F.) in Andhra Pradesh. Pesticides, 18(9) : 23-27.
2. Murugesan, K. and Dhingra, S. 1995. Variability in resistance pattern of various groups of insecticides evaluated against Spodoptera litrua (Fabricius) during a period spanning over three decades. J. ent. Res., 19(4) : 313-319.
3. Rao, G.R. and Dhingra, S. 1996. Relative susceptibility of different larval instars of Spodoptera litura (Fabricius) to some synthetic pyrethroids. J. ent. Res., 20(2) : 103-108.
4. Armes, N.J., Wightman, J.A., Jadhav, D.R. and Ranga Rao, G.V. (1997) Status of insecticide resistance in Spodoptera litura in Andhra Pradesh. Pestic. Sci., 50: 240-248.
5. Rao, G.R. and Dhingra, S. 2000. Variation in the efficacy of mixed formulation comprising vegetables oils and synthetic pyrethroids against susceptible (Delhi) and resistant (Guntur) larval populations of Spodoptera litura (Fabricius). J. ent. Res., 24(2) : 115-120.
6. Kranthi, K.R., Jadhav, D.R., Wanjari, R.R., Shaker, Ali, S. and Russel, D. (2002) Insecticide resistance in five major insect pests of cotton in India. Crop Prot., 21 : 449-460.
7. Kodandaram M. H. and Dhingra, S. 2003 Comparative toxicity of ester and non-ester pyrethroids against Spodoptera litura (Fab) Pestic. Res. J., 15 (1) : 23-25
8. Finney, D.J. (1971) Probit analysis. Cambridge University, London pp. 333.
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