ARTICLE IN PRESS

0261-2194/$ - se

doi:10.1016/j.cr

�Correspondculture and Bio

Tel.: +9241 26

E-mail addr

Crop Protection 27 (2008) 523–531

www.elsevier.com/locate/cropro

Susceptibility of Pakistani populations of cotton aphid Aphis gossypii(Homoptera: Aphididae) to endosulfan, organophosphorus and

carbamate insecticides

Mushtaq Ahmad�, M. Iqbal Arif

Central Cotton Research Institute, Multan, Pakistan

Received 14 February 2007; received in revised form 4 August 2007; accepted 6 August 2007

Abstract

The Pakistani field populations of Aphis gossypii were assessed from 1996 to 2004 for their susceptibility to endosulfan,

organophosphates (monocrotophos, dimethoate, profenofos, chlorpyrifos, quinalphos, parathion-methyl, pirimiphos-methyl and ethion)

and carbamates (carbaryl, methomyl, thiodicarb, furathiocarb and carbosulfan) using a leaf-dip bioassay method. Generally, there was a

very low resistance to endosulfan, monocrotophos, profenofos, chlorpyrifos, quinalphos, pirimiphos-methyl, carbaryl and methomyl,

and a low to moderate resistance to dimethoate, parathion-methyl and thiodicarb. Some of the populations had a very high resistance to

parathion-methyl, ethion and thiodicarb. However, no resistance was found to the carbamate aphidicides furathiocarb and carbosulfan.

Correlation analysis demonstrated positive correlation of LC50s within but not between the two insecticide groups (1) endosulfan,

profenofos, chlorpyrifos and parathion-methyl and (2) monocrotophos, dimethoate, pirimiphos-methyl, ethion, carbaryl, methomyl and

thiodicarb. This pattern of cross-resistance among organophosphates and carbamates, which are normally considered to have the same

mode of action, is very useful for devising an insecticide resistance management strategy to mitigate resistance problems in A. gossypii

and deserve further investigation at the resistance mechanism level.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Aphis gossypii; Insecticide resistance; Endosulfan; Organophosphates; Carbamates; Pakistan

1. Introduction

Cotton or melon aphid Aphis gossypii Glover (Homo-ptera: Aphididae) is a late-season pest of cotton inPakistan. It infests cotton when the crop is maturing inOctober and November. At this stage, its damage is duenot only to its direct feeding but also to deterioration oflint quality caused by the deposition of sticky honey dewon the opening bolls. Sooty mould later develops on thishoney dew, thus resulting in poor-quality cotton.

Under favourable environmental conditions, when daytemperatures drop below 35 1C, A. gossypii populationsexplode quickly, for it reproduces parthenogenetically and

e front matter r 2007 Elsevier Ltd. All rights reserved.

opro.2007.08.006

ing author. Present address: Nuclear Institute for Agri-

logy, Jhang Road, Faisalabad, Pakistan.

53417.

ess: mush_a@yahoo.com (M. Ahmad).

its life cycle is short. Cotton aphid is highly variable inappearance. Larger, darker forms (which are producedwhen environmental conditions are nearly optimum foraphids) are highly reproductive, and are especially capableof producing rapid population increases. Its colonies thusmultiply exponentially towards the end of the cottonseason in Pakistan, because the populations of parasitoidsand predators are at their lowest levels due to frequentapplications of insecticides to control cotton pests.

A. gossypii usually appears on cotton and cucurbitaceousvegetables in early October in the Punjab plains ofPakistan. Cotton is harvested in December but itsinfestations continue on vegetables till it disappears bythe end of April. From May to September, it has neverbeen found on any host in the hot plains of the Punjab.Observations suggest that each year winged A. gossypii

migrate in October from cooler mountainous and sub-mountainous regions to the plains of Punjab including

ARTICLE IN PRESSM. Ahmad, M. Iqbal Arif / Crop Protection 27 (2008) 523–531524

Multan. So, each year the aphid population collectedfrom Multan was considered to be a different migrantpopulation.

Since A. gossypii populations infest cotton after thecotton spraying is over in Pakistan, they are selected byinsecticides applied on vegetables but not by insecticidalapplications on cotton. As a result of its persistent directand indirect exposure to insecticidal sprays on vegetables,A. gossypii developed a high level of resistance to almost allthe pyrethroids in Pakistan (Ahmad et al., 2003). Thepresent studies were conducted to ascertain the status ofA. gossypii resistance to other conventional insecticideclasses, viz. endosulfan, organophosphates (OPs) (mono-crotophos, dimethoate, profenofos, chlorpyrifos, quinal-phos, parathion-methyl, pirimiphos-methyl and ethion)and carbamates (carbaryl, methomyl, thiodicarb, furathio-carb and carbosulfan) in Pakistani field populations.

2. Materials and methods

2.1. Insects

Samples of A. gossypii were collected annually fromcotton at the Central Cotton Research Institute, Multan, incentral Pakistan from 1996 to 2004, and tested directly,without further rearing, in October and Novembereach year. Cotton leaves and terminals laden with aphidswere picked up at 8–10 random spots across a 5-acreblock of cotton to randomize collections. Apterous adultaphids were collected from the leaves in the laboratory fortesting.

2.2. Insecticides

The formulated insecticides used for leaf-dip bioassayswere endosulfan (Thiodan, 350 g/l EC [emulsifiable con-centrate]; Bayer CropScience, Leverkusen, Germany),monocrotophos (Nuvacron, 400 g/l SL [soluble concen-trate]; Syngenta, Basle, Switzerland), dimethoate (Systoate,400 g/l EC; Bayer), profenofos (Curacron, 500 g/l EC;Syngenta), chlorpyrifos (Lorsban, 400 g/l EC; Dow AgroS-ciences, Indianapolis, IN, USA), quinalphos (Ekalux,250 g/l EC; Syngenta), parathion methyl (Folidol M,500 g/l EC; Bayer), pirimiphos-methyl (Actellic, 500 g/lEC; Syngenta), ethion (468 g/l EC; FMC, Philadelphia,PA, USA), carbaryl (Sevin, 850 g/kg SP [water-solublepowder]; Bayer), methomyl (Lannate, 400 g/kg SP; DuPontAgricultural Products, Wilmington, DE, USA), thiodicarb(Larvin, 800 g/kg DF [dry flowable]; Bayer), furathiocarb(Deltanet, 400 g/l EC; Syngenta) and carbosulfan (Advan-tage, 200 g/l EC; FMC).

2.3. Bioassays

Serial dilutions as ppm of the active ingredient of the testcompounds were prepared using distilled water. Cotton(Gossypium hirsutum) leaf discs (5-cm diameter) were cut

and dipped into the test solutions for 10 s with gentleagitation and then allowed to dry on paper towel on bothsides. They were then placed abaxial surface uppermost on1% agar beds in 5-cm diameter Petri dishes. Ten apterousadult aphids were released onto each leaf disc. Fivereplicates of 10 aphids were used for each concentrationand 4–11 serial concentrations were used for each testinsecticide. The same number of leaf discs per treatmentdipped into distilled water was used as an untreatedcheck. Before and after treatment, aphids were maintainedat a constant temperature of 2572 1C with a photoperiodof 14 h.

2.4. Statistical analysis

Mortality was scored 48 h after aphids were placed ontreated leaf discs. Adults failing to exhibit movement aftera gentle prod were considered as dead. Data were correctedfor control mortality using Abbott’s (1925) formula andanalysed by probit analysis (Finney, 1971) using thesoftware package POLO-PLUS (LeOra Software, 2003).The LC50 and LC90 values were calculated and any twovalues compared were considered significantly different iftheir respective 95% confidence limits (CLs) did notoverlap. Resistance factors (RFs) were determined bydividing the lethal concentration (LC) values of eachinsecticide by the corresponding LC values for the 1996population. The 95% CLs for the RFs were determinedaccording to Robertson and Preisler (1992). To interpretcross-resistance spectra among the insecticides tested,correlation coefficients for pairwise correlation oflogLC50s were calculated by the Pearson correlationformula according to Snedecor and Cockran (1989) usingthe MSTAT statistical computer programme (MSTAT-C,1989).

3. Results

3.1. Baselines

The 1996 population was used as a reference strain tocalculate baseline LC values for all the insecticides testedherein. There was no reason to think that the populationwas truly susceptible to the insecticides tested, but it mostlyexhibited lower LC values and higher slopes of regressionlines than most of the subsequent populations (Table 1).The baseline LC values of carbamates furathiocarb andcarbosulfan, which were similar, were the lowest, indicatingthat these compounds were the most active insecticidesagainst A. gossypii. The baseline LC values for mono-thiophosphates profenofos, chlorpyrifos, quinalphos andparathion-methyl were very similar and there were non-significant differences among their LC50s. Since a truesusceptible strain is hard to obtain these days, the resultsfrom the 1996 population can be used as a baseline for anyfuture resistance monitoring of A. gossypii using the leaf-dip bioassay.

ARTIC

LEIN

PRES

S

Table 1

Toxicity of selected insecticides against field populations of Aphis gossypii collected from cotton at Multan, Pakistan

Insecticide Year tested No. tested Fit of probit line LC50 (mg l�1) RF at LC50 LC90 (mg l�1) RF at LC90

Slope7SE w2 df P (95% CL) (95% CL) (95% CL) (95% CL)

Endosulfan 1996 300 2.0570.19 3.89 4 0.42 2.48 (2.00�3.07) 1.0 10.5 (7.77�15.6) 1.0

1997 401 1.3670.12 4.03 6 0.67 2.96 (2.18�3.96) 1.2 (0.8�1.7) 26.1 (17.5�44.4) 2.5 (1.4�4.4)

1998 351 1.5870.14 2.77 5 0.74 10.2 (7.96�13.0) 4.1 (2.9�5.7) 65.8 (46.1�106) 6.3 (3.7�11)

1999 300 1.7470.17 2.58 4 0.63 6.68 (5.27�8.47) 2.7 (1.9�3.7) 36.5 (25.8�58.4) 3.5 (2.0�5.9)

2000 300 1.6270.16 2.09 4 0.72 7.79 (6.09�10.0) 3.1 (2.3�4.4) 47.9 (32.8�80.3) 4.6 (2.6�8.0)

2001 350 1.8770.17 2.91 5 0.71 7.90 (6.46�9.64) 3.2 (2.4�4.3) 38.2 (28.4�56.8) 3.6 (2.2�6.0)

2002 300 1.7170.24 0.68 4 0.95 17.5 (11.5�24.3) 7.1 (4.6�11) 98.5 (67.3�173) 9.4 (5.3�17)

2003 350 1.5070.15 4.60 5 0.47 18.7 (13.8�24.9) 7.5 (5.2�11) 134 (92.2�220) 13 (7.4�22)

2004 400 1.6870.18 3.25 6 0.78 22.0 (16.0�28.7) 8.9 (6.2�13) 127 (91.8�199) 12 (7.3�20)

Monocrotophos 1996 250 3.2870.36 0.68 3 0.88 10.4 (8.75�12.3) 1.0 25.5 (20.4�34.8) 1.0

1997 499 1.0570.10 3.49 8 0.90 35.8 (23.4�52.0) 3.4 (2.2�5.3) 598 (374�1100) 23 (13�42)

1998 400 1.5370.13 4.77 6 0.57 101 (78.8�129) 9.7 (7.3�13) 693 (487 �1091) 27 (17�44)

1999 350 1.6770.16 3.41 5 0.64 57.7 (43.8�74.6) 5.5 (4.1�7.6) 338 (240�534) 13 (8.2�21)

2000 400 1.8870.18 2.05 6 0.92 48.7 (38.5�60.5) 4.7 (3.5�6.3) 233 (175�342) 9.1 (6.0�14)

2002 300 1.3570.16 3.30 4 0.51 43.2 (30.4�59.8) 4.2 (2.9�6.1) 383 (240�758) 15 (8.2�28)

2003 350 1.7870.17 2.05 5 0.84 21.7 (16.6�27.8) 2.1 (1.5�2.8) 114 (82.3�176) 4.5 (2.8�7.0)

2004 350 1.8070.16 2.97 5 0.70 5.07 (4.04�6.38) 0.5 (0.4�0.6) 26.2 (18.9�40.2) 1.0 (0.6�1.6)

Dimethoate 1996 251 2.5270.36 3.02 3 0.39 11.4 (6.72�16.6) 1.0 36.9 (24.2�87.4) 1.0

1997 400 1.3470.12 4.35 6 0.63 66.0 (48.0�88.6) 5.8 (3.8�8.5) 600 (405�1005) 16 (9.1�28)

1998 204 2.9570.35 1.65 3 0.65 464 (381�567) 41 (30�57) 1259 (968�1839) 34 (22�55)

1999 250 2.6770.38 2.68 3 0.44 186 (142�233) 16 (11�23) 563 (429�847) 15 (9.5�25)

2000 553 1.0170.08 7.99 9 0.54 160 (114�221) 14 (9.1�21) 2919 (1844�5190) 79 (42�142)

2001 450 1.5770.16 4.94 7 0.67 156 (114�204) 14 (9.3�20) 1028 (732�1626) 28 (17�46)

2002 300 1.9770.19 5.00 4 0.29 104 (73.2�149) 9.1 (6.8�13) 466 (294�982) 13 (8.0�21)

2003 553 0.8870.08 3.95 9 0.91 87.0 (53.8�132) 7.6 (4.5�13) 2496 (1442�5187) 68 (33�137)

2004 250 2.9070.31 2.50 3 0.48 78.6 (65.7�94.2) 6.9 (5.1�9.4) 217 (170�305) 5.9 (3.8�9.2)

Profenofos 1996 350 1.8570.16 3.13 5 0.68 5.40 (4.32�6.78) 1.0 26.5 (19.3 �40.4) 1.0

1997 450 1.3170.10 4.80 7 0.68 1.46 (1.12�1.91) 0.3 (0.2�0.4) 13.8 (9.42�22.6) 0.5 (0.3�0.9)

1998 400 1.6770.15 3.83 6 0.70 10.5 (8.15�13.3) 1.9 (1.4�2.7) 61.4 (44.7�93.2) 2.3 (1.4�3.8)

1999 300 1.9870.19 5.27 4 0.26 13.2 (9.11�19.0) 2.4 (1.8�3.3) 58.5 (37.0�124) 2.2 (1.3�3.7)

2000 300 1.6870.22 3.63 4 0.46 13.9 (9.35�19.1) 2.6 (1.7�3.9) 80.4 (55.3�137) 3.0 (1.7�5.4)

2001 400 1.5870.13 4.25 6 0.64 16.0 (12.6�20.4) 3.0 (2.1�4.2) 103 (73.0�161) 3.9 (2.3�6.7)

2002 350 1.7970.21 5.68 5 0.34 16.7 (10.6�23.9) 3.1 (2.1�4.4) 86.8 (55.9�178) 3.3 (1.9�5.6)

2003 400 1.6970.14 4.20 6 0.65 20.9 (17.0�25.8) 3.9 (2.8�5.3) 120 (87.8�179) 4.5 (2.7�7.5)

2004 501 1.1470.09 7.78 8 0.48 42.7 (31.4�57.8) 7.9 (5.4�12) 569 (371�979) 21 (12�39)

Chlorpyrifos 1996 250 2.6470.31 2.78 3 0.43 4.80 (3.94�5.82) 1.0 14.7 (11.3�21.5) 1.0

1997 350 1.7970.16 4.0 5 0.55 0.91 (0.72�1.14) 0.2 (0.1�0.3) 4.71 (3.39�7.26) 0.3 (0.2�0.5)

1998 551 0.9170.07 4.45 9 0.88 1.55 (1.04�2.24) 0.3 (0.2�0.5) 40.0 (24.0�76.7) 2.7 (1.4�5.3)

1999 350 1.5470.15 3.72 5 0.59 3.69 (2.74�4.85) 0.8 (0.5�1.1) 25.0 (17.3�41.0) 1.7(1.0�2.9)

2000 501 1.1270.09 4.91 8 0.77 5.31 (3.83�7.26) 1.1 (0.8�1.6) 74.8 (48.6�129) 5.1 (2.8�8.9)

M.

Ah

ma

d,

M.

Iqb

al

Arif

/C

rop

Pro

tection

27

(2

00

8)

52

3–

53

1525

ARTIC

LEIN

PRES

STable 1 (continued )

Insecticide Year tested No. tested Fit of probit line LC50 (mg l�1) RF at LC50 LC90 (mg l�1) RF at LC90

Slope7SE w2 df P (95% CL) (95% CL) (95% CL) (95% CL)

2001 350 1.1870.15 2.62 5 0.76 10.7 (6.67�16.0) 2.2 (1.4�3.6) 131 (78.1�275) 8.9 (4.5�18)

2002 350 2.0270.23 2.11 5 0.83 23.3 (17.5�30.0) 4.9 (3.5�6.7) 100 (75.5�147) 6.8 (4.3�11)

2003 350 1.7170.21 5.25 5 0.39 24.8 (16.1�35.4) 5.2 (3.6�7.2) 140 (86.6�322) 9.5 (5.4�16)

2004 400 1.5670.13 5.57 6 0.47 30.6 (24.3�38.1) 6.4 (4.7�8.5) 204 (147�312) 14 (8.4�22)

Quinalphos 1996 250 2.8070.29 2.58 3 0.46 4.21 (3.51�5.06) 1.0 12.1 (9.45�17.0) 1.0

1997 350 1.5570.14 6.41 5 0.27 0.28 (0.20�0.42) 0.07 (0.05�0.09) 1.91 (1.14�4.22) 0.2 (0.09�0.3)

1998 350 1.5970.14 5.71 5 0.34 4.73 (3.34�6.73) 1.1 (0.8�1.5) 30.4 (18.8�62.5) 2.5 (1.5�4.1)

1999 450 1.6170.12 4.59 7 0.71 1.92 (1.55�2.37) 0.5 (0.3�0.6) 12.0 (8.77�17.8) 1.0 (0.6�1.6)

2000 451 1.1770.10 3.93 7 0.79 8.93 (6.44�12.2) 2.1 (1.5�3.0) 112 (73.0�196) 9.3 (5.2�16)

2001 300 1.8570.22 2.45 4 0.65 8.89 (6.34�11.8) 2.1 (1.5�3.0) 43.8 (31.4�69.2) 3.6 (2.2�5.9)

2002 400 1.5370.17 3.30 6 0.77 8.85 (6.16�11.9) 2.1 (1.4�3.1) 60.8 (42.7�98.5) 5.0 (3.1�8.3)

2003 450 1.2770.11 4.08 7 0.77 8.10 (5.97�10.8) 1.9 (1.3�2.7) 82.0 (55.1�136) 6.8 (3.9�11)

2004 400 1.4570.13 2.61 6 0.86 12.9 (9.65�16.9) 3.1 (2.2�4.3) 98.0 (68.0�158) 8.1 (4.9�14)

Parathion-methyl 1996 300 2.2870.26 1.82 4 0.77 6.82 (5.45�8.39) 1.0 24.9 (18.9�36.9) 1.0

1997 350 1.6470.14 4.67 5 0.46 30.2 (23.8�38.5) 4.4 (3.2�6.2) 182 (128�289) 7.3 (4.4�12)

1998 350 1.8770.16 2.45 5 0.78 23.0 (18.4�28.7) 3.4 (2.5�4.6) 111 (81.8�166) 4.5 (2.8�7.2)

1999 350 1.7770.16 3.90 5 0.56 54.3 (43.1�68.3) 8.0 (5.8�11) 289 (209�440) 12 (7.0�19)

2000 250 2.8070.29 3.06 3 0.38 150 (110�205) 22 (17�29) 431 (296�826) 17 (11�27)

2001 301 2.0770.21 1.56 4 0.82 161 (127�202) 24 (17�33) 672 (500�1000) 27 (17�43)

2002 300 2.1470.26 4.41 4 0.35 168 (109�235) 25 (18�34) 667 (446�1343) 27 (17�43)

2003 300 2.1870.31 1.80 4 0.77 190 (131�252) 28 (19�41) 735 (541�1144) 30 (18�48)

2004 500 1.0670.13 9.08 8 0.34 543 (283�893) 80 (49�130) 8874 (4719�24377) 356 (177�721)

Pirimiphos-methyl 1996 300 2.6870.38 2.08 4 0.72 10.4 (7.86�13.0) 1.0 31.4 (24.7�44.7) 1.0

1997 500 0.9570.08 7.44 8 0.49 153 (105�220) 15 (9.4�23) 3456 (2029�6940) 110 (56�217)

1998 400 1.5770.13 4.42 6 0.62 108 (85.1�138) 10 (7.3�15) 706 (500�1105) 22 (14�36)

1999 304 1.8570.20 2.91 4 0.57 86.9 (65.2�112) 8.4 (5.8�12) 428 (309�673) 14 (8.5�22)

2000 350 1.5670.14 3.72 5 0.59 34.5 (26.9�44.3) 3.3 (2.3�4.7) 228 (157�373) 7.3 (4.4�12)

2001 350 1.9870.28 5.12 5 0.40 43.2 (25.9�61.6) 4.2 (2.8�6.0) 191 (126�399) 6.1 (3.7�9.7)

2002 300 1.7370.19 3.76 4 0.44 15.1 (11.3�19.6) 1.5 (1.0�2.1) 82.9 (58.3�135) 2.7 (1.6�4.4)

2003 400 1.4970.13 4.49 6 0.61 15.1 (11.9�18.9) 1.5 (1.0�2.0) 110 (78.1�172) 3.5 (2.1�5.6)

2004 450 1.1270.10 2.84 7 0.90 14.4 (9.62�20.4) 1.4 (0.9�2.2) 198 (127�352) 6.3 (3.6�11)

Ethion 1996 300 2.8470.29 1.94 4 0.75 14.1 (11.8�17.0) 1.0 40.0 (31.5�55.7) 1.0

1997 353 1.4870.14 4.59 5 0.47 131 (97.7�173) 9.3 (6.6�13) 967 (662�1609) 24 (14�41)

1998 250 3.0470.33 1.79 3 0.62 3028 (2543�3611) 215 (168�276) 7981 (6314�11073) 200 (136�296)

1999 350 1.6370.14 5.24 5 0.39 12985 (9324�17992) 921 (700�1271) 79122 (50834�150462) 1978 (1258�3303)

2000 500 1.0370.10 5.30 8 0.73 275 (177�403) 20 (13�32) 4893 (3014�9311) 122 (68�242)

2002 404 1.4470.16 7.41 6 0.28 140 (81.7�216) 9.9 (6.8�15) 1087 (644�2502) 27 (16�47)

2003 400 1.4970.12 4.15 6 0.66 91.7 (71.3�118) 6.5 (4.8�9.0) 664 (464�1055) 17 (10�28)

2004 450 1.1770.09 5.75 7 0.57 60.3 (45.2�80.3) 4.3 (3.1�6.1) 744 (486�1285) 19 (11�34)

Carbaryl 1996 350 1.8370.16 4.15 5 0.53 7.75 (6.18�9.71) 1.0 38.8 (28.4�58.4) 1.0

1997 549 0.9670.09 5.31 9 0.81 54.2 (32.3�83.3) 7.0 (4.1�12) 1183 (720�2265) 30 (15�57)

1998 251 2.4670.31 3.83 3 0.28 69.2 (40.4�105) 8.9 (6.4�12) 230 (144�616) 5.9 (3.6�9.6)

1999 200 4.8570.65 0.49 2 0.78 118 (103�136) 15 (12�20) 217 (182�284) 5.6 (3.7�8.6)

M.

Ah

ma

d,

M.

Iqb

al

Arif

/C

rop

Pro

tection

27

(2

00

8)

52

3–

53

1526

ARTIC

LEIN

PRES

S2000 350 1.6870.15 4.35 5 0.50 64.5 (50.9�81.7) 8.3 (6.0�12) 371 (265�581) 9.6 (5.7�17)

2002 451 1.2270.11 3.69 7 0.81 50.6 (34.9�70.7) 6.5 (4.3�10) 565 (372�975) 15 (8.1�27)

2003 450 1.5070.12 8.62 7 0.28 17.5 (13.0�23.7) 2.3 (1.6�3.1) 125 (80.9�230) 3.2 (1.9�5.5)

2004 400 1.0970.12 8.24 6 0.22 3.00 (1.44�5.36) 0.4 (0.2�0.6) 44.8 (21.7�150) 1.2 (0.6�2.4)

Methomyl 1996 250 2.7070.28 3.57 3 0.31 8.82 (6.21�12.4) 1.0 26.3 (17.5�55.0) 1.0

1997 451 1.2270.09 5.00 7 0.66 80.2 (60.7�106) 9.1 (6.5�13) 900 (591�1541) 34 (20�60)

1998 551 1.0870.14 7.07 9 0.63 107 (60.4�162) 12 (7.3�20) 1640 (1022�3250) 62 (33�117)

1999 300 1.9870.25 2.87 4 0.58 41.1 (29.9�53.7) 4.7 (3.3�6.5) 183 (132�289) 7.0 (4.3�11)

2000 350 1.9570.17 2.58 5 0.76 33.2 (26.7�41.4) 3.8 (2.8�5.0) 151 (111�227) 5.7 (3.6�9.2)

2001 350 1.4470.23 9.95 5 0.08 17.6 (4.71�33.9) 2.0 (1.3�3.2) 136 (64.3�1093) 5.2 (2.8�10)

2002 400 1.4070.12 5.07 6 0.53 19.2 (15.1�24.3) 2.2 (1.6�3.0) 158 (109�259) 6.0 (3.6�10)

2003 450 1.4870.14 4.38 7 0.74 13.9 (10.1�18.3) 1.6 (1.1�2.2) 102 (72.0�161) 3.9 (2.4�6.3)

2004 350 1.7670.19 6.62 5 0.25 8.39 (5.37�12.2) 1.0 (0.7�1.3) 45.0 (28.1�99.3) 1.7 (1.0�2.8)

Thiodicarb 1996 242 2.5170.28 1.51 4 0.82 11.4 (9.11�14.2) 1.0 36.9 (27.9�54.4) 1.0

1997 401 1.1670.10 2.30 6 0.89 292 (218�393) 26 (18�37) 3717 (2346�6830) 101 (54�188)

1998 250 2.5370.26 2.37 3 0.50 1157 (954�1405) 101 (75�135) 3721 (2850�5384) 101 (63�157)

1999 350 2.1470.19 5.64 5 0.34 329 (254�428) 29 (21�38) 1308 (909�2254) 35 (22�55)

2000 550 0.9170.06 8.29 9 0.51 193 (139�268) 17 (11�25) 4922 (2952�9366) 133 (69�259)

2002 350 1.6470.14 5.12 5 0.40 150 (108�207) 13 (9.3�18) 908 (583�1724) 25 (14�41)

2003 347 1.6270.15 3.83 5 0.57 50.8 (38.6�65.8) 4.5 (3.1�6.3) 315 (222�502) 8.5 (5.0�14)

2004 350 1.6370.14 4.84 5 0.44 21.5 (16.9�27.4) 1.9 (1.4�2.6) 132 (93.6�207) 3.6 (2.1�5.9)

Furathiocarb 1996 300 2.8370.28 5.16 4 0.27 0.50 (0.38�0.64) 1.0 1.41 (1.01�2.40) 1.0

1997 399 1.5170.14 5.53 6 0.48 0.51 (0.38�0.67) 1.0 (0.7�1.4) 3.61 (2.50�5.85) 2.6 (1.6�4.2)

1998 349 1.7070.18 3.33 5 0.65 0.23 (0.17�0.30) 0.5 (0.3�0.6) 1.31 (0.93�2.09) 0.9 (0.6�1.5)

1999 350 1.8270.16 3.63 5 0.60 0.58 (0.46�0.72) 1.2 (0.9�1.5) 2.93 (2.14�4.42) 2.1 (1.3�3.2)

2000 350 1.4570.13 8.58 5 0.13 0.12 (0.07�0.19) 0.2 (0.2�0.3) 0.91 (0.49�2.57) 0.6 (0.4�1.1)

2002 400 1.7070.17 4.07 6 0.67 0.60 (0.45�0.78) 1.2 (0.9�1.7) 3.42 (2.49�5.22) 2.4 (1.6�3.8)

2003 250 2.7370.29 1.98 3 0.58 0.74 (0.61�0.88) 1.5 (1.2�1.9) 2.17 (1.69�3.05) 1.5 (1.0�2.3)

2004 350 1.7770.18 1.75 5 0.88 0.47 (0.36�0.59) 0.9 (0.7�1.3) 2.49 (1.81�3.84) 1.8 (1.1�2.8)

Carbosulfan 1996 301 2.1470.20 2.94 4 0.57 0.43 (0.35�0.53) 1.0 1.69 (1.27�2.49) 1.0

1998 450 1.1970.10 3.94 7 0.79 0.29 (0.21�0.40) 0.7 (0.5�1.0) 3.49 (2.31�5.92) 2.1 (1.2�3.7)

1999 350 2.0070.18 4.07 5 0.54 0.53 (0.43�0.66) 1.2 (0.9�1.7) 2.33 (1.73�3.44) 1.4 (0.9�2.2)

2000 400 1.6270.13 6.07 6 0.42 0.17 (0.13�0.23) 0.4 (0.3�0.6) 1.07 (0.71�1.90) 0.6 (0.4�1.1)

2002 400 1.5370.16 3.07 6 0.80 0.52 (0.37�0.69) 1.2 (0.8�1.8) 3.59 (2.53�5.75) 2.1 (1.3�3.6)

2003 400 1.7070.14 3.29 6 0.77 0.48 (0.39�0.59) 1.1 (0.8�1.5) 2.72 (2.01�4.02) 1.6 (1.0�2.6)

2004 400 1.6270.16 3.51 6 0.74 0.31 (0.23�0.40) 0.7 (0.5�1.0) 1.92 (1.38�2.99) 1.1 (0.7�1.9)

M.

Ah

ma

d,

M.

Iqb

al

Arif

/C

rop

Pro

tection

27

(2

00

8)

52

3–

53

1527

ARTICLE IN PRESSM. Ahmad, M. Iqbal Arif / Crop Protection 27 (2008) 523–531528

3.2. Endosulfan

The 1997 population of A. gossypii had a similar LC50

value of endosulfan to that of the 1996 referencepopulation; however, it had a 2.5-fold higher LC90 valuethan the 1996 population (Table 1). The other populationstested showed a very low level of resistance to endosulfan,in spite of the fact that endosulfan had been commonlyused in Pakistan during the 1980s and 1990s. There was asignificant increase in the LC50s and LC90s of endosulfanduring the years 2002–2004, but still the resistance levelsremained very low at the LC50s.

3.3. Organophosphates

All the populations of A. gossypii showed a very lowlevel of resistance to monocrotophos at LC50s. However,monocrotophos resistance levels at LC90s were moderatein the years 1997 and 1998 and low in 1999 and 2002(Table 1). Because of the declining use of monocrotophosin Pakistan during the 1990s and 2000s, its RF valuesdemonstrated a declining trend so that the 2004 populationwas even more susceptible to monocrotophos than the 1996reference population.

The A. gossypii populations of 1997 and 2002–2004exhibited a very low level of resistance to dimethoate,whereas the populations of 1999–2001 had a low resistanceat LC50s (Table 1) but the 2000 and 2003 populationsdemonstrated a high dimethoate resistance at LC90s. The1998 population showed a moderate resistance to dimetho-ate, 41-fold at LC50 and 34-fold at LC90. Based on LC50

values, dimethoate resistance decreased after a peak in1998. This was most probably correlated with the declininguse of dimethoate, which has now gone out of the Pakistanimarket.

Resistance to profenofos remained very low from 1997to 2004 (Table 1). The 1997 population was rather moresusceptible to profenofos than the reference population of1996. Nevertheless, no resistance of A. gossypii wasobserved to chlorpyrifos at LC50 up to the year 2000.Indeed the 1997 population was more susceptible tochlorpyrifos than the reference population of 1996. In theyears 2001–2004, chlorpyrifos resistance developed to verylow levels. There was a progressive increase of LC valuesfor both profenofos and chlorpyrifos due to the fact thatthe use of these OP insecticides had been increasing inPakistan over the years.

The populations of A. gossypii collected during1996–1999 were susceptible to quinalphos, and the 1997population was more susceptible than our referencepopulation of 1996 (Table 1). The populations collectedduring 2000–2004 had a very low level of resistance toquinalphos. This resistance may be due to cross-resistancefrom other OPs, because quinalphos is no longer in use inPakistan.

Resistance to parathion-methyl developed progressivelyin A. gossypii. During 1997–1999 it was very low, during

2000–2003 it became moderate and during 2004 it reacheda very high level (Table 1). Resistance to pirimiphos-methylwas low during 1998 and 1999 and very low during2000–2004. The 1997 population exhibited a 15-foldresistance to pirimiphos-methyl at LC50 but a 110-foldresistance at LC90. The use of parathion-methyl has beenvery minimal, and pirimiphos-methyl has never been usedin Pakistan. The resistance to these insecticides thereforeseems to be a case of cross-resistance from other OPs.There was a very high resistance to ethion in A. gossypii

in the years 1998 and 1999 (Table 1). In the year 2000,ethion resistance was moderate at LC50 but very high atLC90. However, this resistance dropped to very low tomoderate levels during the years 2002–2004. Ethion use hasbeen very limited in Pakistani agriculture. It was never usedalone, always in a mixture with pyrethroids. A very highresistance to ethion also represents a cross-resistancepattern from other OPs.

3.4. Carbamates

Generally, a very low level of resistance to carbaryl wasobserved in all the populations of A. gossypii tested from1997 to 2003, with no resistance in 2004 (Table 1).However, the RFs of carbaryl for 1997 and 2002populations were 30 and 15, respectively, at LC90s.Resistance to methomyl was low in 1997 and 1998 at

LC50s but high at LC90s. During 1999–2003, a very lowresistance was recorded to methomyl. As with carbaryl, nomethomyl resistance was found in the A. gossypii popula-tion of 2004.Resistance to thiodicarb was higher than to carbaryl and

methomyl. Thiodicarb resistance remained moderate tovery high during 1997–2000 and low during 2002 (Table 1).It then dropped to very low levels during 2003 and 2004.Over the years, the use of carbaryl, methomyl andthiodicarb had been declining and so the resistance tothese carbamates declined. The application of thesecarbamates is currently very limited.All the populations of A. gossypii tested from 1996 to

2004 were found susceptible to furathiocarb and carbo-sulfan (Table 1). The populations from 1998 and 2000 hadsignificantly lower LC50 values for both furathiocarb andcarbosulfan than the reference population. The use offurathiocarb and carbosulfan has been very limited inPakistan. Since these insecticides are expensive, they areused against aphids only when population pressure isparticularly high.

3.5. Correlation between LC50 values of insecticides

Paired comparisons of the logLC50s of insecticides testedfor all the populations showed positive correlations amonga first group of endosulfan, profenofos, chlorpyrifos andparathion-methyl (Table 2), suggesting a cross-resistanceamong these insecticides. However, the LC50 values of thisgroup of insecticides were not correlated with that of a

ARTICLE IN PRESS

Table 2

Pairwise correlation coefficient comparisons between logLC50 values of the insecticides tested on field populations of Aphis gossypii (superscripts denote

significance of the regression)

Insecticide Endosulfan Monocrotophos Dimethoate Profenofos Chlorpyrifos Parathion-methyl Pirimiphos-methyl Ethion Carbaryl Methomyl

Monocrotophos �0.095ns

Dimethoate 0.471ns 0.7160.05

Profenofos 0.8640.01 �0.275ns 0.285ns

Chlorpyrifos 0.7590.05 �0.551ns �0.173ns 0.8170.05

Parathion-methyl 0.8460.01 �0.256ns 0.314ns 0.7350.05 0.7340.05

Pirimiphos-methyl �0.355ns 0.7020.05 0.580ns �0.546ns �0.8380.01 �0.313ns

Ethion 0.092ns 0.7470.05 0.8120.05 0.075ns �0.392ns 0.041ns 0.7030.05

Carbaryl �0.196ns 0.9570.01 0.6200.1 �0.346ns �0.557ns �0.227ns 0.7150.05 0.7490.05

Methomyl �0.272ns 0.8500.01 0.6710.1 �0.515ns �0.8110.05 �0.330ns 0.9450.01 0.6860.1 0.8120.05

Thiodicarb �0.006ns 0.9260.01 0.8420.01 �0.251ns �0.599ns �0.123ns 0.8480.01 0.8070.05 0.8760.01 0.9450.01

M. Ahmad, M. Iqbal Arif / Crop Protection 27 (2008) 523–531 529

second group comprising monocrotophos, dimethoate,pirimiphos-methyl, ethion, carbaryl, methomyl and thio-dicarb, indicating no cross-resistance between these groupsof insecticides. Chlorpyrifos resistance was somewhatnegatively correlated with pirimiphos-methyl and metho-myl. Carbamate insecticides were positively correlatedamong themselves and also with monocrotophos, dimetho-ate, pirimiphos-methyl and ethion, showing a cross-resistance among this group of insecticides. OPs of thesecond group also exhibited a positive correlation amongthemselves except between dimethoate and pirimiphos-methyl. The occurrence of two divergent patterns of cross-resistance within the OPs tested herein indicates that morethan one mechanism exists for imparting resistance to OPsin A. gossypii, and that the two OP groups can be treatedseparately for resistance management purposes.

4. Discussion

In general, there was a very low to low resistance toendosulfan, most OPs and carbamates in A. gossypii;however, many populations showed a moderate to highresistance to the OPs dimethoate, parathion-methyl andethion, and the carbamate thiodicarb (Table 1). Resistanceof A. gossypii to endosulfan, OPs and carbamates has alsobeen documented from China (Sun et al., 1987; Li et al.,2003), Russia (Khodzhaev et al., 1985), Central AsianStates (Sukhoruchenko, 1996), Europe (Delorme et al.,1997; Ioannidis, 1998; Nauen and Elbert, 2003), Egypt(Din, 2003), Israel (Ishaaya and Mendelson, 1987), Sudan(Gubran et al., 1992), Korea (Kim et al., 1987), Japan(Saito et al., 1995), Australia (Herron et al., 2001), NewZealand (Martin et al., 1997) and USA (Kerns and Gaylor,1992; O’Brien et al., 1992; Grafton-Cardwell et al., 1992,1997; Hollingworth et al., 1994).

The aphid populations tested during 1996–2004 exhib-ited a very low resistance (o10) to endosulfan and most ofthe OPs and carbamates in the present study. The samepopulations, tested during 1997–2000, were highly resistantto pyrethroids (Ahmad et al., 2003). This implies that theremay be little cross-resistance between pyrethroids andother insecticide classes for any major mechanism(s) in

A. gossypii populations from Pakistan. No cross-resistancewas similarly found by others between pyrethroids and OPs(Mu et al., 1988; Han, 1993; Wu and Liu, 1994; Saito et al.,1995) or carbamates (Liu, 1987; Han, 1993) in A. gossypii.The present study indicates that there were marked

differences in the development of resistance in the samepopulations of A. gossypii within a chemical class such asthe carbamates and OPs. Within carbamates, furathiocarband carbosulfan showed no increased resistance, whereas asignificantly increased resistance was discernible to carbaryl,methomyl and thiodicarb. Furathiocarb and carbosulfancontain benzofuran, whereas methomyl and thiodicarbcontain thioacetamide as leaving components in theirstructural formulae. Benzofuran may perhaps be lesscompromised by enzymatic attack by resistant A. gossypii.Among OPs, a very low resistance was found to mono-crotophos, profenofos, chlorpyrifos, quinalphos and pir-imiphos-methyl, but a moderate to very high resistance todimethoate, parathion-methyl and ethion in many popula-tions. There is no clear biochemical basis for thisdifferentiation, but differences in resistance within achemical class are probably due to the specificity ofresistance mechanisms and are potentially very useful forthe management of resistant populations of A. gossypii.The genotypes resistant to one insecticide can be killed bythe use of an insecticide from another resistance groupfrom the same chemical class.The major mechanisms responsible for resistance to OPs

and carbamates in A. gossypii were found to be insensitivityof acetylcholinesterase and increased activity of carbox-ylesterase enzymes (Sun et al., 1987, 1994; Gubran et al.,1992; O’Brien et al., 1992; Saito et al., 1995; Silver et al.,1995; Moores et al., 1996; Delorme et al., 1997; Hanet al., 1998; Saito and Hama, 2000; Din, 2003; Li et al.,2003). Reduced cuticular penetration has also been foundresponsible for imparting OP and carbamate resistance inA. gossypii (Sun et al., 1987; Gubran et al., 1992). Therewas evidence that carbamate resistance in A. gossypii wascorrelated with the enhanced activity of mixed functionoxidases (Saito et al., 1995).Molecular changes in acetylcholinesterase (AChE)

leading to target-site resistance to OP and carbamate

ARTICLE IN PRESSM. Ahmad, M. Iqbal Arif / Crop Protection 27 (2008) 523–531530

insecticides have recently been identified in aphids. AnS431F mutation in AChE1 has been associated with OPand carbamate resistance in A. gossypii (Andrews et al.,2004; Benting and Nauen, 2004). Benting and Nauen(2004) have further found that recombinantly expressedAChE1 from A. gossypii carrying the S431F mutation isinsensitive to pirimicarb and omethoate, but sensitive todemeton-S-methyl and hypersensitive to carbofuran. Thismay provide a molecular explanation of the selectivity ofthe S431F mutation, providing specific insensitivity to awide range of OPs and carbamates as may be the case inour study. Another study demonstrated that two muta-tions, A302S in Ace1 and F139L in Ace2, might beassociated with resistance to OPs in A. gossypii (Li andHan, 2004).

For successful aphid control on cotton, an insecticideresistance management strategy needs to be devised andimplemented. The insecticides showing no or very lowresistance in our laboratory bioassays were found fullyeffective for controlling A. gossypii in the field, and,therefore, they can play a key role in the managementstrategy. Biological control of aphids should be an integralpart of the strategy, for aphids are a good host for manypredators. During mid- and late season, when insecticidesare being sprayed on cotton, predator populations arenegligible. When sprays for lepidopterous pests stop late inthe season, A. gossypii appears in large numbers on cottonin Pakistan. Predator populations especially lacewings alsofollow and become abundant, but the damage has alreadybeen done before lacewings can overcome aphid popula-tions. For encouraging predator populations to synchro-nize with aphid outbreaks towards the end of the season,new insecticides that are considered soft on predators(Horowitz and Ishaaya, 2004) such as indoxacarb andspinosad for bollworms, and insect growth regulators,buprofezan and pyriproxyfen for whitefly and benzoylphe-nyl ureas for armyworms, are recommended for use in thelate season. The new chemistries, which have novel modesof action unrelated to those of conventional chemistries,are not expected to be cross-resistant to OPs/carbamates orendosulfan at the target site and can therefore be a good fitin the integrated pest management programmes forcontrolling aphids.

Acknowledgements

The technical assistance of Munir Ahmad, RashidMehmood, Abid Hameed Khan, Tanveer Hussain, Tabas-sam Nurin, Hina Rana and Qudsia Naz is acknowledgedwith thanks.

References

Abbott, S.W., 1925. A method of computing the effectiveness of an

insecticide. J. Econ. Entomol. 18, 265–267.

Ahmad, M., Arif, M.I., Denholm, I., 2003. High resistance of field

populations of the cotton aphid Aphis gossypii Glover (Homoptera:

Aphididae) to pyrethroid insecticides in Pakistan. J. Econ. Entomol.

96, 875–878.

Andrews, M.C., Callaghan, A., Field, L.M., Williamson, M.S., Moores,

G.D., 2004. Identification of mutations conferring insecticide-insensi-

tive AChE in the cotton-melon aphid, Aphis gossypii Glover. Ins. Mol.

Biol. 13, 555–561.

Benting, J., Nauen, R., 2004. Biochemical evidence that an S431F

mutation in acetylcholinesterase-1 of Aphis gossypii mediates resistance

to pirimicarb and omethoate. Pest Manage. Sci. 60, 1051–1055.

Delorme, R., Auge, D., Bethenod, M.T., Villatte, F., 1997. Insecticide

resistance in a strain of Aphis gossypii from Southern France. Pestic.

Sci. 49, 90–96.

Din, H.A.E., 2003. Toxicity of some insecticides on field populations

of three aphid species in relation to carboxylestarase activity. Assiut

J. Agric. Sci. 34, 153–161.

Finney, D.J., 1971. Probit Analysis, third ed. Cambridge University Press,

UK.

Grafton-Cardwell, E.E., Leigh, T.F., Bentley, W.J., Goodell, P.B., 1992.

In the San Joaquin Valley-cotton pests have become resistant to

commonly used pesticides. California Agric. 46, 4–7.

Grafton-Cardwell, E.E., Godfrey, L.D., Brindley, W.A., Goodell, P.B.,

1997. Status of lygus bug and cotton aphid resistance in the San

Joaquin Valley. In: Proceedings of Beltwide Cotton Conferences,

pp. 1072–1074.

Gubran, E.M.E., Delorme, R., Auge, D., Moreau, J.P., 1992. Insecticide

resistance in cotton aphid Aphis gossypii (Glov.) in the Sudan Gezira.

Pestic. Sci. 35, 101–107.

Han, Z.J., 1993. Mechanism and countermeasures of deltamethrin

resistance in Aphis gossypii Glover. Resist. Pest Manage. Newslett. 5,

10–11.

Han, Z.J., Moores, G.D., Denholm, I., Devonshire, A.L., 1998.

Association between biochemical markers and insecticide resistance

in the cotton aphid, Aphis gossypii Glover. Pestic. Biochem. Physiol.

62, 164–171.

Herron, G.A., Powis, K., Rophail, J., 2001. Insecticide resistance in Aphis

gossypii Glover (Homoptera: Aphididae), a serious threat to Aus-

tralian cotton. Aust. J. Entomol. 40, 85–91.

Hollingworth, R.G., Tabashnik, B.E., Ullman, D.E., Johnson, M.W.,

Messing, R., 1994. Resistance of Aphis gossypii (Homoptera:

Aphididae) to insecticides in Hawaii: spatial patterns and relation to

insecticide use. J. Econ. Entomol. 87, 293–300.

Horowitz, A.R., Ishaaya, I., 2004. Biorational insecticides—mechanisms,

selectivity and importance in pest management. In: Horowitz, A.R.,

Ishaaya, I. (Eds.), Insect Pest Management. Springer, Berlin, Heidel-

berg, Germany, pp. 1–28.

Ioannidis, P.M., 1998. Resistance of Aphis gossypii (Homoptera:

Aphididae) to insecticides. In: Proceedings of the Second World

Cotton Research Conference. J. Econ. Entomol., pp. 759–763.

Ishaaya, I., Mendelson, Z., 1987. The susceptibility of the melon aphid

Aphis gossypii to insecticides during the cotton growing season.

Hassadeh 67, 1772–1773.

Kerns, D.L., Gaylor, M.J., 1992. Insecticide resistance in field populations

of the cotton aphid (Homoptera: Aphididae). J. Econ. Entomol. 85,

1–8.

Khodzhaev, S.T., Roslavtseva, S.A., Abdulaev, E., Sobchak, M.N., 1985.

Resistance of the cotton aphid to insecticides. Zashchita Rastenii 12,

30.

Kim, G.H., Shin, W.K., Ahn, J.W., Cho, K.Y., 1987. Susceptibility

of several insecticides on three aphids. Kor. J. Plant Prot. 26,

83–88.

LeOra Software, 2003. Poloplus, a User’s Guide to Probit or Logit

Analysis. LeOra Software, Berkeley, USA.

Li, F., Han, Z.J., 2004. Mutations in acetylcholinesterase associated with

insecticide resistance in the cotton aphid, Aphis gossypii Glover. Ins.

Biochem. Mol. Biol. 34, 397–405.

Li, F., Han, Z.J., Tang, B., 2003. Insensitivity of acetylcholinesterase and

increased activity of esterase in the resistant cotton aphid, Aphis

gossypii Glover. Acta Entomol. Sin. 46, 578–583.

ARTICLE IN PRESSM. Ahmad, M. Iqbal Arif / Crop Protection 27 (2008) 523–531 531

Liu, R.X., 1987. A study on the resistance of Aphis gossypii to pyrethroids.

China Cottons 1, 42–45.

Martin, N.A., Workman, P.J., Callaghan, O.M., 1997. Melon aphid

(Aphis gossypii) resistance to pesticides. In: Proceedings of the 50th

New Zealand Plant Protection Conference, pp. 405–408.

Moores, G.D., Gao, X.W., Denholm, I., Devonshire, A.L., 1996.

Characterisation of insensitive acetylcholinesterase in insecticide-

resistant cotton aphids, Aphis gossypii Glover (Homoptera: Aphidi-

dae). Pestic. Biochem. Physiol. 56, 102–110.

MSTAT-C, 1989. User’s Guide to MSTAT-C—A Microcomputer

Program for the Design, Management, and Analysis of Agronomic

Research Experiments. Michigan State University, East Lansing,

USA.

Mu, L.Y., Wang, K.Y., Jiang, C.L., Shen, H.M., Jiang, J.L., Chen, Q.Y.,

Deng, Q.R., Lin, G.F., 1988. Studies of resistance to fenvalerate,

omethoate and mixture agent by Aphis gossypii. Sci. Agric. Sin. 21,

18–26.

Nauen, R., Elbert, A., 2003. European monitoring of resistance to

insecticides in Myzus persicae and Aphis gossypii (Hemiptera:

Aphididae) with special reference to imidacloprid. Bull. Entomol.

Res. 93, 47–54.

O’Brien, P.J., Abdel-Aal, Y.A., Ottea, J.A., Graves, J.B., 1992. Relation-

ship of insecticide resistance to carboxylesterases in Aphis gossypii

(Homoptera: Aphididae) from midsouth cotton. J. Econ. Entomol. 85,

651–657.

Robertson, J.L., Preisler, H.K., 1992. Pesticide Bioassays with Arthro-

pods. CRC Press, Boca Raton, FL, USA.

Saito, T., Hama, H., 2000. Carboxylesterase isozymes responsible for

organophosphate resistance in the cotton aphid, Aphis gossypii Glover

(Homoptera: Aphididae). Appl. Entomol. Zool. 35, 171–175.

Saito, T., Hama, H., Suzuki, K., 1995. Insecticide resistance in clones of

the cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), and

synergistic effect of esterase and mixed-function oxidase inhibitors.

Jpn. J. Appl. Entomol. Zool. 39, 151–158.

Silver, A.R.J., van Emden, H.F., Battersby, M., 1995. A biochemical

mechanism of resistance to pirimicarb in two glasshouse clones of

Aphis gossypii. Pestic. Sci. 43, 21–29.

Snedecor, G.W., Cockran, W.G., 1989. Statistical Methods, eighth ed.

Iowa State University Press, IA, USA.

Sukhoruchenko, G.I., 1996. Review of the problem of resistance of cotton

pests to pesticides in Central Asia and Azerbaijan at the beginning of

the 90’s. Entomol. Obozrenie 75, 3–15.

Sun, Y.Q., Feng, G.L., Yuan, J.G., Zhu, P., Gong, K.Y., 1987.

Biochemical mechanism of resistance of cotton aphids to organopho-

sphorus insecticides. Acta Entomol. Sin. 30, 13–20.

Sun, Y.Q., Feng, G.L., Yuan, J.G., Gong, K.Y., 1994. Insecticide

resistance of cotton aphids in North China. Entomol. Sin. 1, 242–250.

Wu, K.M., Liu, Q.X., 1994. Some biological characteristics of a

cotton aphid strain resistant to fenvalerate. Acta Entomol. Sin. 37,

137–144.