TECHNICAL BULLETIN 179 ISSN 0070·2315

RESPONSE OF SUSCEPTIBLE AND RESiSTANT STRAINS

OF SPODOPTERA LITTORALIS TO CONVENTIONAL

INSECTICIDES IN CYPRUS

P. Charalambous and N. Iordanou

AGRICULTURAL RESEARCH INSTITUTE

MINISTR:Y OF AGRICULTURE, NATURAL RESOURCES

AND THE ENVIRONMENT

NICOSIA CYPRUS

APRIL 1997

Editor - in Chief

Dr A.P. Mavrogenis, Agricultural Research Institute, Nicosia, Cyprus.

All responsibility for the information in this publication remains with the author(s). The use

of trade names does not imply endorsement of or discrimination against any product by the

Agricultural Research Institute.

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RESPONSE OF SUSCEPTIBLE AND RESISTANT STRAINS OF SPODOPTERA LITTORALIS TO CONVENTIONAL INSECTICIDES IN CYPRUS

P. Charalambous and N. Iordanou

SUMMARY

To study the development of resistance in the field strain of Spodoptera littoralis (Boisduval) larvae to different classes of insecticides, six pyrethoids (decamethrin, cy­permethin, esfenvalerate, fenpropathrin, cyfluthrin, and permethin), two carbamates (carbaryl and methomyl), two organophosphates (chlorpyrifos and methamidophos) and one organochlorine (D.D.T.) were used. The lethal dose (LD50) of the insecticides were determined by topical bioassay against third-instar larvae of the susceptible and re­sistant field strains. Resistance ratio (RR at LD50) indicated that the field strain larvae, collected from a potato field in the Kokkinochoria area that was sprayed with conven­tional insecticides, had developed resistance to all insecticides tested, The levels of re­sistance were very high to decamethrin (6083-fold), to cypermethrin (407 - fold), to es­fenvalerate (313 - fold) and to carbaryl (367 -fold). Intermediate resistance was found to methamidophos (217 - fold), to fenpropathrin (213 - fold) and to D.D.T. (150 - fold). Mild resistance was found to cyfluthrin (45 - fold), to permethrin (40 - fold), and low levels of resistance to methomyl (14 - fold), and to chlorpyrifos (6 - fold). The use of the carbamate insecticide methomyl and of the organophosphates chlorpyrifos and me­thamidophos could lead to manageable resistance of Spodoptera littoralis.

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INTRODUCTION

Spodoptera littoralis (Boisduval) (Lepidopte­ra, Noctuidae), is a major pest of vegetable crops in Cyprus. It causes serious losses to vegetable crops and particularly in potatoes, celery, lucerne, sweet peppers and artichock in the fall. Potato and vegetable crops in Cy­prus are treated with pyrethroid, organophos­phorous and carbamate insecticides against several insect pests during the growing sea­son (April - November).

Previous research (Serghiou, 1971; 1982) showed that the insecticides phosfolan and monocrotophos, the most efficient to control S. littoralis, were partially replaced in the mid seventies by other insecticides, because of their progressive field failure to control S. littoralis larvae, which resulted from the de­velopment of resistance to those insecticides. Zeid et al. (1968) and Abdel-Aal et al. (1977), reported that S. littoralis has the abil­ity of developing resistance to insecticides. Holden (1979) found that a strain of the Egyptian cotton leaf worm S. littoralis, which was already resistant to a range of in­secticides, showed cross-resistance to the py­rethroid permethrin. Electrophysiological studies conducted on sixth instar larvae showed that pyrethroid resistance in a strain of S. littoralis is correlated with decreased sensitivity of the central nervous system in vitro (Gammon, 1980).

Ishaaya and Klein (1990) reported that a cotton field strain of S. littoralis in Israel was 120 and 102 times more resistant than the susceptible laboratory strain to chlorpyrifos and cyperrnethrin, respectively, and was slightly cross-resistant to teflubenzuron (5 times).

The recent decrease in the effectiveness of organophosphorous, pyrethroid and carba­mate insecticides against S. littoralis larvae on potatoes and other vegetable crops, sug­gested a possible development of resistance of this pest to conventional insecticides. The objective of this work was to study the de­velopment of resistance in the field strain of S. littoralis to different classes of insecti­cides.

MATERIALS AND METHODS

Chemicals Formulated insecticides, used in the topi­

cal application bioassay were decamethrin (Decis 2.5% EC, Russel Uglaf), cypermeth­rin (Radex 25% EC, FMC) fenpropathrin (Danitol 10% EC, Sumitomo Chern.), cy­fluthrin (Baythroid 50 SL. Bayer) esfenval­erate (Sumi-alpha 2.5% EC, Sumitromo Chem.), permethrin (Pounce 3.2 EC 38.74%, FMC), chlorpyrifos (Dursban 48% EC, Dow Elanco Chemical Co.) methamidophos (Tamaron 60 SL, Bayer), methomyl (Lan­nate 90 Sp, Dupont), carbaryl (Sevin 85 WP, Rhone Poulenc) and DDT (technical 75.3%, Laboratory of Dr. Ehrenstorfer, GmbH, Ger­many).

Insects Two strains of S. littoralis were used.

The susceptible laboratory strain was ob­tained from the Agrochemical Division of Ciba Geigy (Basel, Switzerland) and the field strain was established with larvae col­lected in October 1993 from a potato field in the Kokkinochoria area that was sprayed with conventional insecticides. Both strains were reared under standard laboratory condi- ­tions at 25±2 °C and 60±7% RH on artificial diet (Navon. 1985) with slight modifications.

Bioassay . In all bioassays, third instar larvae of the

susceptible and field strains were used. For­mulated insecticides were diluted to the de­sired concentration in acetone and insecti­cide solution of 1 ~ll was applied topically on the dorsal surface of each larva, using a 10.0 ~tl Hamilton micro syringe. After treatment, larvae were kept in glass petri dishes and were provided with artificial diet. Three rep­licates, of 10 larvae each, were used per con­centration with five different concentrations per insecticide. Mortality was assessed 24 hours after treatment. Dose-mortality regres­sions were analysed by probit analysis (SAS Institute 1990). Resistance ratio was deter­mined by dividing the LD50 values obtained for the resistant field strain by those obtained for the susceptible laboratory strain.

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Table 1. Susceptibility levels..of the susceptible (S) laboratory and resistant (R) field strain of Spodoptera littoralis to several pyrethroid insecticides

No of LDsoa Fiducial limits Insecticide Strain insects Slope± SE (!1g/larvae) (95%) RRb

Decamethin S 150 1.37± 0.26 0.00036 0.00024-0.00052 6.083 R 150 1.23± 0.29 2.19 1.350-6.048

Cypermethrin S 150 2.02± 0.30 0.0013 0.00099-0.0017 407 R 150 5.78± 0.98 0.53 0.490-0.594

Estenvalerate S 150 1.45± 1.09 0.0036 313 R 150 3.49± 0.57 1.128 0.935-1.311

Fenpropathrin S 150 2.75± 0.36 0.0019 0.0016-0.0024 213 R 150 1.84± 0.30 0.405 0.288-0.537

Cyfluthrin S ISO 1.30± 0.27 0.00081 0.00023-0.0052 45 R ISO 4.09± 1.07 0.037 0.032-0.049

Permethrin S ISO 0.73± 0.11 0.0016 0.0006-0.0034 40 R 150 2.37± 0.48 0.064 0.028-0.131

Carbaryl S ISO 4.08± 1.39 0.452 >367 R ISO >166

Methamidophos S ISO 4.28± 0.62 0.038 0.033-0.043 217 R ISO 1.57± 0.27 8.28 5.648-12.255

D.D.T. S ISO ~.63± 0.506 4.79 3.786 r 5.825 150 R 150 10.62± 4.69 718.61

Methomyl S ISO 2.76± 0.49 0.014 0.0101-0.0176 14 R 150 3.13± 0.50 0.198 0.154-0.243

Chlorpyrifos S 150 2.58± 0.40 0.048 0.0363-0.0602 6 R .150 0.32± 0.27 0.281 0.032-0.049

aLDso: dose which causes 50% mortality of the population. bResistance ratio: LDso of resistant strainjLDso of susceptible strain.

RESULTS AND DISCUSSION

Comparison of LD50 values for the two strains revealed that the field strain had de­veloped resistance to insecticides of all ma­jor classes. The level of resistance was very high to the pyrethroids decamethrin (6083­fold), cypermethrin (407-fold) and esfenval­erate (313-fold) and to the carbamate carba­ryl (>367-fold) (Table 1). Intermediate resis­tance was found for the organophosphate methamidophos (217-fold), the pyrethroid fenpropathrin (213-fold) and the organoch­lorin DDT (l50-fold) (Table 1). Mild resis­tance was found for the pyrethroids cyfluth­rin (45-fold and permethrin (40-fold) (Table I) and low levels of resistance for the carba­mate methomyl (14-fold) and the organoph­osphate chlorpyriphos (6-fold) (Table 1).

The results of these bioassays showed that the field strain of S. littoralis had devel­op'ed multiple resistance. This resistance is due to all major factors responsible for insect resistance to insecticides, like mixed func­tion oxida~e, hydrolyses and reduced sensi­tivity of the target site (kdr) factor. The high levels of the pyrethroid resistance (deca­methrin 6083-fold) and cross-resistance to DDT (250-fold) in the field strain indicated the presence of kdr-type resistance as a fac­tor of pyrethroid resistance.

Resistance to pyrethroid insecticides in different insect species is very common and many workers reported similar results. Priester and Georghiou (1978) have reported a level of resistance higher than 4,000 fold to d-trans permethrin in larvae of Culex pipiens quinquefaciatus, and suggested that reduced

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sensitivity of the target site (kdr-factor) may be the primary source of resistance. Scott and Matsumura (1983) found that resistance to DDT in the German Cockoach is due to the target site insensitivity and that the Kdr­factor confers high levels of resistance to py­rethroids in the same species. A DDT­resistant strain of Boophilus microplus (No­lan et al., 1977) and a DDT - resistant mos­quito strain (Prasittisuk and Busvine, 1977) have shown cross-resistance to pyrethroids. Nicolson and Miller (1985) reported that re­sistance to pyrethroids in field collected strain of the tobacco bud worm Helothis vi­rescens, results from both metabolic and tar­get site insensitivity mechanisms. Pyrethroid resistance in a strain of Spodoptera littoralis is correlated with decreased sensitivity of the central nervous system (kdr-type resistance) (Gammon, 1979). Ishaaya and Klein (1990) found that Spodoptera littoralis larvae, col­lected from a cotton field, showed strong re­sistance to organophosphates and pyrethroids and showed a mild tolerance to benzoylphe­nyl ureas. Riskallash (1983) showed that es­terases (hydrolases) are responsible for py­rethroid resistance in the Spodoptera littoralis larvae.

Our results suggest that pyrethroid insec­ticides should not be used to control field strains of Spodoptera littoralis larvae for several years, since the continuous use of those insecticides will further increase resis­tance levels of field strains to pyrethroids and will increase cross-resistance to other in­secticides from different classes. The use of the organophosphate insecticides chlorpyri­fos and methamidophos and of the carbamate methomyl could lead to manageable resis­tance of Spodoptera littoralis. Searching for new effective, but friendly to the environ­ment, insecticides and particularly insect growth regulators must continue.

ACKNOWLEDGMENTS

We thank Dr P. Stocklin from Ciba Gei­gy, Basel, for the supply of the susceptible strain of S. littoralis, Dr G. Orphanides for the revision of the manuscript and Mr D. Kourris for skilled technical assistance.

REFERENCES

Abdel-Aal, Y.A.I., T.K. Abdel-Raof, and M.A.H. Fahny. 1977. Field induced resistance in Spodoptera littoralis (Boisduval) to cer­tain insecticides. International pest con­trol 19:6-7.

Gammon, D.W. 1980. Pyrethroid resistance in a strain of Spodoptera littoralis is correlat­ed with decreased sensitivity of the CNS in vitro. Pesticide Biochemistry and Phys­iology 13:53-62.

Holden, J.S. 1979. Absorption and metabolism of permethrin and cypermethrin in the cock­roach and the cotton-leafworm larvae. Pesticide Science 10:295.

Ishaaya, I., and M. Klein. 1990. Responce of sus­ceptible laboratory and resistant field stains of Spodoptera littoralis (Lepidopte­ra: Noctuidae) to teflubenzuron. Journal ofEconomic Entomology 83:59-62.

Navon, A. 1985. Spodoptera littoralis. Handbook of insect rearing, vol. 2:469-475 (P. Singh and R.F. Moore, eds). Elserier, Amsterdam.

Nicholson, R.A., and T.A. Miiler. 1985. Multifac­torial resistance to trans-permethrin in field collected stains of the tobacco bud worm Heliothis virescens SF. Pesticide Science 16:561-562.

Nolan, J.Y., W.J. Roulston, and R.H. Wharton. 1977. Resistance of synthetic pyrethroids in a resistant strain of Boophilus micro­plus. Pesticide Science 8:484-486.

Prasittisuk, c., and J.R. Busvine. 1977. DDT­resistant mosquito strains with cross­resistance to pyrethroids. Pesticide Sci­ence 8:527-533.

Priester, T.M., and G.P. Georghiou. 1978. Induc­tion of high resistance to permethrin in Culex pipiens quinquefasciatus. Journal ofEconomic Entomology 71: 197-200.

Riskallash, M.R. 1983. Esterases and resistance to synthetic pyrethroids in the Egyptian cotton leafworm. Pesticide Biochemistry and Physiology 19:184-189.

SAS Institute. 1990. SAS User's Guide: Statistics, Version 6, 4th edition. SAS Institute Cary, NC.

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Serghiou, C.S. 1971. Laboratory and field evalua­tion of insecticides against Spodoptera lit­toralis (Boisduval) larvae. Journal ofEco­nomic Entomology 64: 115-116.

Serghiou, C.S. 1982. The effectiveness of synthet­ic pyrethroids against Spodoptera littoral­is (Boisduval) larvae. Technical Bulletin 42, Agricultural Research Institute, Nico­sia.5p.

Scott, J.G., and F. Matsumura 1983. Evidence of two types of toxic actions of pyrethroids on susceptible and DDT-resistant German cockroaches. Pesticide Biochemistry and Physiology 19:141-150.

Zeid, M. A.A. Saad, G. Tantarri, and M.E. Elde­trawi. 1968. Laboratory and field evalua­tion of insecticides against the Egyptian cotton leaf worm. Journal of Economic Entomology 61: 1183-1186.

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