Pakistan J. Zool., vol. 43(3), pp. 529-535, 2011.
Field and Laboratory Performance of Transgenic Bt Cotton
Containing Cry1Ac Against Beet Armyworm Larvae (Lepidoptera:
Noctuidae)
Muhammad Arshad* and Anjum Suhail
Department of Agricultural Entomology, University of Agriculture, Faisalabad, Pakistan
Abstract.- The efficacy of transgenic Bt cotton genotype containing Cry1Ac was investigated against beet
armyworm, Spodoptera exigua (Hubner) in the field and laboratory experiments. The results showed that S. exigua
larvae had low susceptibility to Bt cotton. No significant differences in larval densities between transgenic Bt and
conventional cotton under unsprayed conditions were observed and insecticides were used to control the population in
sprayed Bt and non-Bt cotton plots. The laboratory bioassays showed no significant impacts of Bt cotton plant
structures (leaves and flower-bolls) on the larval mortality as compared to conventional non-Bt cotton. However, the
results indicated sublethal effects with significant differences in larval development time and pupal weight.
Key words: Transgenic Bt cotton insecticide, resistance, Cry1Ac, Spodoptera exigua.
INTRODUCTION
Beet armyworm, Spodoptera exigua (Hubner)
is a polyphagous insect pest affecting various
economically important crops (Agrawal et al., 2002)
and in case of severe infestation has caused
significant loss to cotton crop in Pakistan. It
primarily feed on foliage but also feed on fruiting
parts of cotton plant (Eveleens et al., 1973). Larval
feeding on cotton leaves can cause devastating
losses in yield (Adamczyk et al., 1998a). The insect
pest management in cotton is mainly dominated by
the use of broad-spectrum insecticides, which
disrupt the beneficial insect fauna too thus leading
to pest resurgence and outbreaks of secondary pests,
as well as risk to human health and environment
(Yousefi, 2000). It is estimated that in Pakistan,
farmers spend US$300 million on pesticides
annually, of which more than 80% is used on cotton,
especially for bollworms (Rao, 2007).
One option to reduce the insecticide use on
cotton is the exploitation of transgenic Bt cotton as a
component of integrated pest management (Gore et
al., 2001). Bt cotton, the first transgenic non-food
crop, has provided a specific, safe and effective tool
for the control of lepidopterous pests (Shelton et al.,
2002; Mendelsohn et al., 2003; Wu and Guo, 2005).
Bt cotton expressing the Cry1Ac protein has been
______________________
*
Corresponding author: [email protected]
0030-9923/2011/0003-0529 $ 8.00/0
Copyright 2011 Zoological Society of Pakistan.
available commercially in the US since 1996 and is
also being grown in Mexico, Columbia, Australia,
China, India, Argentina and South Africa (James,
2006). Growing of transgenic cotton is a new
technology in Pakistan agriculture. Toxic genes
from Bt plant lead to the suppressions of major
lepidopterous pests’ population (Carriere et al.,
2003). However, transgenic Bt cotton with Cry1Ac
proved not to be effective against Spodoptera spp.
(Ponsard et al., 2002; Hofs et al., 2004; Yu et al.,
2004), hence insecticide applications are needed to
control this pest in Bt cotton (Smith, 1997). The
addition of Cry2Ab along with Cry1Ac in Bollgard
II appears to be the most effective against
Spodoptera spp. (Adamczyk et al., 2001; Stewart et
al., 2001). Abro et al. (2004) reported 13.3 to
53.3% mortality of Spodoptera spp. on different Bt
cotton (Cry1Ac) varieties. Some other field studies
(Jeyakumar et al., 2007; Wan et al., 2008) have
shown no significant difference in Spodoptera
exigua larval population between Bt (Cry1Ac) and
non-Bt cotton under unsprayed conditions.
Furthermore Burris et al. (1994) found no
significant differences in leaf area consumed,
mortality or pupal weight of beet armyworm larvae
by feeding on Bt (Bollgard I) and non-Bt cotton
plant structures in the laboratory. Low larval
mortality was observed in Spodoptera spp. feeding
on Bt cotton (Cry1Ac) leaves (Ashfaq and Young,
1999; Henneberry et al., 2001; Abro et al., 2004),
but found significant reduction in larval & pupal
530
M. ARSHAD AND A. SUHAIL
weight as well as size and increased larval
development time (Ashfaq et al., 2000; Henneberry
et al., 2001; Guo et al., 2003; Huang et al., 2007;
Wan et al., 2008). There has been concern over the
effectiveness of Bt cotton against beet armyworm as
there is a spatial and temporal variation in Cry1Ac
toxin in Bt cotton plant structures (Adamczyk and
Gore, 2004). A number of studies have shown that
Spodoptera exigua is not susceptible to Bt cotton
containg Cry1Ac toxin so, there is a chance that this
pest may become the major and alarming pest in Bt
cotton field. As transgenic crops may perform
differently under different ecological conditions so,
there is a need to determine the efficacy of
transgenic Bt cotton containing Cry1Ac against beet
armyworm under laboratory conditions and in
experimental field plots.
MATERIALS AND METHODS
Field experiments
Experimental study area and design
The field experiments were conducted for
two cotton seasons from 2007-08 at Postgraduate
Agriculture Research Station (PARS), Faisalabad,
Punjab, Pakistan (31º 21.52 North and 72º 59.40
East), where wheat and cotton are commonly
intercropped. The experimental fields were laid out
in a randomized complete block design (RCBD)
consisting of four treatments each with four
replications. Each replicated plot was about 0.05 ha
(hectare). A gap of 5-m was left between plots to
avoid the influence of treatments on insect
population in neighbouring plots (Men et al., 2003).
The transgenic Bt cotton line, “IR-FH-901”
containing Cry1Ac insecticidal protein of Bacillus
thuringiensis obtained from National Institute of
Biotechnology and Genetic Engineering, Faisalabad,
Pakistan (Ahsan and Altaf, 2009) was compared
with its parent non-transgenic, conventional cotton
cultivar, “FH-901”. The experimental area selected
was isolated from other sprayed cotton fields to
reduce the chance of insecticidal drift across the
unsprayed area. The seed rate was used to expect the
plant population of 60,000 per ha with row to row
and plant to plant distance of 0.75 and 0.25 m
respectively. The experimental fields were
maintained according to the recommended
agronomic practices for this area. The treatments
included were; 1) transgenic Bt cotton without
insecticide application (Bt cotton unsprayed), 2)
transgenic Bt cotton with insecticide application (Bt
cotton sprayed), 3) non transgenic cotton without
insecticide application (non-Bt cotton unsprayed), 4)
non transgenic cotton with insecticide application
(non-Bt cotton sprayed). The insecticides used in the
sprayed plots of Bt and non-Bt cotton were
Lufenuron (50EC) @ 200ml/acre and Chlorpyrifos
(40EC) @ 1000ml/acre.
Sampling
The surveillance of cotton crop was initiated
at the seedling emergence and continued on weekly
basis up to the mid October. This resulted in at least
18 sampling dates. A plant inspection method was
used and larval population was recorded on whole
plant on weekly basis by selecting 15 plants at
random in each replicate plot.
Laboratory experiments
Plant culture
The transgenic Bt-cotton line “IR-FH-901”
containing Cry1Ac and its non-transgenic parent
cultivar “FH-901” were cultured in this study. The
cotton plants were grown in pots in a green-house at
25 ºC, 50-70% RH, and a photoperiod of 14:10 (L:
D) h. Plants were kept free from any insecticide
treatment.
Insect’s culture
The larval colony of S. exigua was collected
from the cotton fields and was reared on artificial
diet up to pupation. After adults’ emergence, moths
were maintained in plastic cages (30x30X30 cm)
and nappy liner strips were provided for oviposition.
Adults were provided with 10% honey/water
solution on cotton swab for feeding. The liners were
removed daily and eggs laid on liner strips were
kept for hatching. The insect culture was maintained
for three generations under control conditions at
27°C with a 75% R.H. and a photoperiod of 14:10
(L: D) h. Newly hatched larvae were used for
feeding bioassay.
Experimental procedure
The experiments were
laid
out
in
a
Bt COTTON PERFORMANCE AGAINST BEET ARMYWORM
531
randomized complete block design (RCBD) with
four replications, with 25 larvae in each replicate.
The treatments included were; a) larvae fed on
leaves of non Bt cotton, b) larvae fed on leaves of Bt
cotton, c) larvae fed on flowers of non-Bt cotton
until the third instar, then fed with young bolls of
non-Bt cotton, d) larvae fed on flowers of Bt cotton
until the third instar, then fed with young bolls of Bt
cotton.
The cotton leaves were obtained from the
third or fourth main stem node from terminal
portion of the plants at 40 d after seedling
emergence, while the reproductive parts (including
fresh bloom and young bolls < 2.5 cm diameter)
were obtained from the plants during the
reproductive phase. Plant parts (leaves, flowers and
bolls) of Bt and non-Bt cotton were brought into the
laboratory and were dipped in 0.4% javelle water
(sodium hypochlorite) for 10 min to kill the
pathogens and then rinsed with water before the
feeding bioassay (Men et al., 2005). One day old,
first instar larvae of
S. exigua were placed
individually on each of the plant parts, in an
individual 8cm x 2.5cm glass tube and tube was
covered with cotton blug. Plant parts were changed
daily until the larvae pupated. The numbers of live
and dead larvae were checked daily. Larval
mortality was recorded in all instars and cumulative
mortalities were calculated. Pupae formed from
larvae in different treatments were removed using
feather-light forceps and weighed after one day of
pupation, using a digital microbalance.
variance (ANOVA) and means were separated using
Tukey’s honestly significant difference (HSD) test
using SPSS (SPSS Institute, Chicago, IL, USA).
Statistical analysis
Field experiments
The data on larval population of S. exigua in
different treatments were analyzed using analysis of
variance (ANOVA) and means were separated by
using Tukey’s honestly significant difference (HSD)
test. All analysis was done using SPSS (SPSS
Institute, Chocago, II., USA) and STATISTICA-6
software. The multifactor effects of year, variety
and pesticide were analyzed using GLM procedure
in STATISTICA-6 statistical software.
Factors
Laboratory experiments
Data were analyzed using analysis of
RESULTS
Seasonal abundance of S. exigua larvae in fields
The larval density remained high during mid
August and late September in almost all treatments
(Figs. 1 A, B). However, pooled data of all the
observations showed a significant difference in
larval number between treatments (F = 19.55; df =
3; P = 0.00). The larval density during 2006 was
lower in sprayed plots of Bt and non-Bt cotton
(1.91and 2.10 larvae/15 plants respectively) as
compared to unsprayed Bt and non-Bt cotton (3.29
and 3.57 larvae/15 plants, respectively) (Fig. 2).
While, in 2007 larval density remained low
throughout the observation periods and did not
cause economic damage. Bt cotton did not prove so
effective against armyworm and insecticides were
used to control this pest both in sprayed Bt and nonBt plots (Fig. 1B).
A summary of multi-factor analysis showed
that only year and pesticide significantly influenced
(P < 0.05) the larval density, whereas variety had no
significant (P > 0.05) effects on the larval
population density. No significant differences were
found in all possible interactions (Table I).
Table I.-
Multi-factor effects of year, variety and
pesticide on the mean seasonal abundance of
armyworm.
Year
Variety
Pesticide
Year × Variety
Year × Pesticide
Variety × Pesticide
Year × Variety × Pesticide
Larvae
F-values
P-values
25.62*
3.36
101.84*
0.02
3.83
0.51
0.12
0.001
0.082
0.001
0.873
0.062
0.484
0.742
Significant difference indicated by *P < 0.05
Laboratory experiments
Laboratory experiments were carried out to
study the impact of Bt (IR-FH-901) and non-Bt
532
M. ARSHAD AND A. SUHAIL
Bt cotton unsprayed
Bt cotton sprayed
Non-Bt cotton unsprayed
Non-Bt cotton sprayed
12
10
8
6
4
2
0
15-Oct
8-Oct
1-Oct
17-Sep
17-Sep
24-Sep
10-Sep
10-Sep
3-Sep
27-Aug
20-Aug
13-Aug
6-Aug
30-Jul
23-Jul
16-Jul
24-Jun
-4
9-Jul
-2
2-Jul
Number of larvae per 15 plants
14
Sampling Dates: 2006
A
12
Bt cotton unsprayed
Bt cotton sprayed
Non-Bt cotton unsprayed
Non-Bt cotton sprayed
Number of larvae per 15 plants
10
8
6
4
2
0
15-Oct
8-Oct
1-Oct
24-Sep
3-Sep
27-Aug
20-Aug
13-Aug
6-Aug
30-Jul
23-Jul
16-Jul
9-Jul
24-Jun
-4
2-Jul
-2
Sampling Dates: 2007
B
Fig. 1 Seasonal abundance (Mean ± SE) of armyworm larvae in Bt and non-Bt cotton during 2006 with spraying
dates; 15 August and 5 September (A), 2007; spraying dates, 25 August and 8 September (B).
(FH-901) cotton plant structures (leaves and flowerbolls) on the biological traits (larval mortality, larval
development time and pupal weight) of S.
exigua.The results indicated no significant
differences (P > 0.05) in larval mortality of 1stinstar (F = 0.80, df = 3, P = 0.517); 2nd-instar (F =
3.18, df = 3, P = 0.063); 3rd-instar (F = 2.68, df = 3,
P = 0.094); 4th-instar (F = 2.76, df = 3, P = 0.088)
and 5th-instar (F = 3.06, df = 3, P = 0.069) larvae
fed with Bt and non-Bt cotton leaves and flowerbolls (Table II). In general, survival remained high
in all the treatments (84-87%). However a
significant difference was found in larval
development (F = 226.89, df = 3, P = 0.001)
between Bt and non-Bt cotton plant structures
(Table III). The inhibitory effects of Bt cotton on the
growth of larvae were more obvious than the lethal
effects. Larvae that were fed on non-Bt cotton,
Bt COTTON PERFORMANCE AGAINST BEET ARMYWORM
completed development faster than those fed on Bt
cotton. A comparison of average larval period
indicated that larval period increased on Bt cotton
leaves and flower-bolls (17.75 and 17.52 days
respectively) compared with non-Bt cotton leaves
and flower-bolls (14.82 and 14.57 days
respectively). Similarly, a marked difference was
found in pupal weight (F = 145.95; df = 3, 12; P =
0.001) of larvae fed Bt and non-Bt cotton. Pupal
weight was reduced and the average pupal weight
was significantly (P < 0.05) higher on non-Bt cotton
leaves (0.139 g) compared to average pupal weight
on Bt cotton leaves (0.098 g) (Table III).
Table III.-
533
Larval development time and pupal weight of
Spodoptera exigua fed with leaves and flowersbolls of Bt and non-Bt cotton.
Treatment
Non-Bt cotton
leaves
Bt cotton leaves
Non-Bt cotton
flowers-bolls
Bt cotton flowersbolls
Mean
development
time (days) ± SE
Mean pupal
weight
(g) ± SE
14.82±0.13a
0.139±0.001c
17.75±0.06b
14.57±0.08a
0.098±0.001a
0.141±0.007c
17.52±0.15b
0.107±0.003b
Means ± SE followed by the same letters within a column are
not significantly different (P > 0.05; Tukey’s HSD).
Bt cotton unsprayed
Non-Bt cotton unsprayed
b
b
Number of larvae per 15 plants
4
Bt cotton sprayed
Non-Bt cotton sprayed
DISCUSSION
b
3.5
b
3
2.5
a
a
a
a
2
1.5
1
0.5
0
2006
2007
Fig. 2. Seasonal abundance (Overall mean
± SE) of armyworm larvae in 2006 and 2007,
bars indicated by different letters are
significantly different (Tukey’s HSD, P < 0.05).
Table II.-
Instars
Percent cumulative mortality (Mean ± SE) of
larval instars of Spodoptera exigua fed with
leaves and flowers-bolls of Bt and non-Bt
cotton.
Non-Bt
cotton
Leaves
Bt cotton
Flowers-bolls
Non-Bt
Bt cotton
cotton
I
1.00±0.58a
1.50±0.50a
1.50±0.50a
2.00±0.00a
II
5.00±0.58a
6.50± .50a
6.00±0.00a
7.00±0.58a
III
11.00±0.58a
12.50±0.50a
10.00±0.82a
11.00±0.58a
IV
14.00±0.82a
14.50±0.50a
11.50±0.96a
12.50±0.96a
V
15.50±0.96a
16.00±0.82a
13.00±1.00a
13.50±0.50a
Means ± SE followed by the same letters within the row are not
significantly different (P > 0.05; Tukey’s HSD).
Seasonal abundance of S. exigua larvae
In the field no significant differences in larval
density were found between unsprayed Bt and nonBt cotton plots. These results are in conformity with
previous field studies (Agrawal et al., 2002;
Adamczyk and Gore, 2004; Wan et al., 2008). The
larval populations were significantly higher in
unsprayed Bt and non-Bt cotton than those of
sprayed Bt and non-Bt cotton plots. The differences
were mainly due to the reduced larval number in
sprayed plots of Bt and non-Bt cotton. Similarly,
foliar insecticide applications have been used to
control armyworm in Bt cotton fields in some other
field studies (Hood, 1997; Smith, 1997; Bacheler
and Mott, 1996; Wan et al., 2008). It is noteworthy
that the reduced use of insecticide in Bt cotton may
increase the population of Spodoptera spp.
Therefore; there is a risk that this pest may become
the major pest in Bt cotton fields. It is suggested that
population should be monitored properly to prevent
the crop from economic damage.
Laboratory experiment
The results showed no significant differences
in larval mortalities between Bt and non-Bt cotton
feeding plant structures. Although certain
lepidopterous pests of cotton are controlled by
Bollgard cotton varieties but the Cry1Ac toxin in
534
M. ARSHAD AND A. SUHAIL
Bollgard cotton have exhibited little or no efficacy
against armyworm Spodoptera spp. (Adamczyk et
al., 2001; Henneberry et al., 2001; Stewart et al.,
2001; Chitkowski et al., 2003; Adamczyk and Gore,
2004; Abro et al., 2004; Wan et al., 2008).
However, results indicated the delay in larval
development time on Bt cotton. These results are in
agreement with the previous studies (Mascarehans
and Luttrell, 1997; Stapel et al., 1998; Ashfaq et al.,
2000; Adamczyk et al., 1998b), which showed sublethal effects of Bt cotton on larval development of
armyworm. Similarly Adamczyk et al. (2001)
reported that larvae reared on Cry1Ac diet and on Bt
cotton took significantly more time for pupation
than those of control diet and conventional non-Bt
cotton. The present results contradict with NavaCamberos and Ibarra-Frias (2000) who reported
similar larval development time of S. exigua larvae
on Bt and non-Bt cottons. The current and previous
studies (Adamczyk et al., 1998a) have shown the
significant decrease in pupal weight, produced by
larvae fed on Bt cotton plant structures. As Bt cotton
expressing Cry1Ac is ineffective against Spodoptera
spp. hence, outbreaks of armyworm on Bt cotton
need foliar insecticides applications to keep the
population below economic injury level. These
findings may influence the management strategies
for armyworm in Bt cotton.
ACKNOWLEDGEMENTS
We are grateful to Prof. Dr. Stefan Vidal of
the Georg-August-University in Goettingen,
Germany for reviewing this manuscript and
providing constructive and valuable comments to
improve the results and discussion. We are also
thankful to Dr. Feng Ge, Institute of Zoology,
Chinese Academy of Sciences, Beijing 100080,
China for providing relevant literature to develop
methodology of the experiments and Dr. Denis J.
Wright, Department of life Sciences, Faculty of
Natural Sciences, Imperial College London, for
training in rearing insects and bioassays. The
research was supported by Higher Education
Commission,
Pakistan
which
is
highly
acknowledgement.
REFERENCES
ABRO, G.H., SYED, T.S., TUNIO, G.M. AND KHUHRO,
M.A., 2004. Performance of transgenic Bt cotton
against insect pest infestation. Biotechnology, 3: 75-81.
ADAMCZYK, J.J., MASCARENHAS, V.J., CHURCH, G.E.,
LEONARD, B.R. AND GRAVES, J.B., 1998a. Cotton
boll susceptibility to fall armyworm and beet
armyworm injury. Proceeding Beltwide Cotton
Conference, San Diego, California, USA, 5-9 January,
2: 1170-1172.
ADAMCZYK, J.J., HOLLOWAY, J.W., CHURCH, G.E.,
LEONARD, B.R. AND GRAVES, J.B., 1998b. Larval
survival and development of the fall armyworm
(Lepidoptera: Noctuidae) on normal and transgenic
cotton expressing the Bacillus thuringiensis CryIA(c)
partial derivative-endotoxin. J. econ. Ent., 91: 539-545.
ADAMCZYK, J.J., ADAMS, L.C. AND HARDEE, D.D.,
2001. Field efficacy and seasonal expression profiles
for terminal leaves of single and double Bacillus
thuringiensis toxin cotton genotypes. J. econ. Ent., 94:
1589-1593.
ADAMCZYK, J.J. AND GORE, J., 2004. Development of
bollworms, Helicoverpa zea, on two commercial
Bollgard(R) cultivars that differ in overall Cry1Ac
levels. J. Insect Sci., 4: 1-5.
AGRAWAL, N., MALHOTRA, P. AND BHATNAGAR, R.K.,
2002. Interaction of gene-cloned and insect cellexpressed aminopeptidase N of Spodoptera litura with
insecticidal crystal protein Cry1C. Appl. environ.
Microbiol., 68: 4583-4592.
AHSAN, R. AND ALTAF, Z., 2009. Development, adoption
and performance of Bt cotton in Pakistan: A review.
Pakistan J. agric. Res., 22: 73-85.
ASHFAQ, M. AND YOUNG, S.Y., 1999. Effect of transgenic
Bt-cotton on larval mortality and development of beet
armyworm,
Spodoptera
exigua
(Lepidoptera:
Noctuidae). Proceeding Beltwide Cotton Conference,
Orlando, Florida, USA, 3-7 January, 2:1232-1234.
ASHFAQ, M., YOUNG, S.Y. AND MCNEW, R.W., 2000.
Development of Spodoptera exigua and Helicoverpa
zea (Lepidoptera: Noctuidae) on transgenic cotton
containing CrylAc insecticidal protein. J. entomol. Sci.,
35: 360-372.
BACHELER, J.S. AND MOTT, D.W., 1996. Potential utility
and susceptibility of transgenic Bt. cotton against
bollworms, European corn borers and stink bugs.
Proceeding Beltwide Cotton Conference, Nashville,
TN, USA, 9-12 January, 2:927-931.
BURRIS, E., GRAVES, J.B., LEONARD, B.R. AND WHITE,
C.A., 1994. Beet armyworms (Lepidoptera: Noctuidae)
in Northeast Luisisana - observations on an uncommon
insect pest. Florida Entomol., 77: 454-459.
CARRIERE, Y., ELLERS-KIRK, C., SISTERSON, M.,
ANTILLA, L., WHITLOW, M., DENNEHY, T.J. AND
TABASHNIK, B.E., 2003. Long-term regional
suppression of pink bollworm by Bacillus thuringiensis
Bt COTTON PERFORMANCE AGAINST BEET ARMYWORM
cotton. Proc. natl. Acad. Sci., USA., 100: 1519-1523.
CHITKOWSKI, R.L., TURNIPSEED, S.G., SULLIVAN, M.J.
AND BRIDGES, W.C., 2003. Field and laboratory
evaluations of transgenic cottons expressing one or two
Bacillus thuringiensis var. kurstaki Berliner proteins for
management of noctuid (Lepidoptera) pests. J. econ.
Ent., 96: 755-762.
EVELEENS, K.G., VAN DEN BOSCH, R. AND EHLER,
L.E., 1973. Secondary outbreak induction of beet
armyworm by experimental insecticide applications in
cotton in California. Environ. Ent., 2: 497-503.
GORE, J., LEONARD, B.R. AND ADAMCZYK, J.J., 2001.
Bollworm (Lepidoptera: Noctuidae) survival on
'Bollgard' and 'Bollgard II' cotton flower buds and
flower components. J. econ. Ent., 94: 1445-1451.
GUO, J., DONG, L. AND WAN, F., 2003. Influence of Bt
transgenic cotton on larval survival of common
cutworm Spodoptera litura. Chinese J. biol. Contr., 19:
145-148.
HENNEBERRY, T.J., JECH, L.F. AND DE LA TORRE, T.,
2001. Effects of transgenic cotton on cabbage looper,
tobacco budworm, and beet armyworm (Lepidoptera:
Noctuidae) larval mortality and development and
foliage consumption in the laboratory. Southw. Ent., 26:
325-338.
HUANG, D., XIA, J., LIU, H., WANG, W., JI, Z. AND
WANG, Q., 2007. Effects of CpTI+Bt transgenic cotton
and Bt transgenic cotton on population increase and
preference of Spodoptera exigua (Hubner). Acta
Phytophyl. Sin., 34: 461-465.
HOOD, E., 1997. The fall armyworm: and I thought we had it
made. Proceeding Beltwide Cotton Conference, New
Orleans, LA, USA, 6-10 January, 1223-1224.
HOFS, J.L., SCHOEMAN, A. AND VAISSAYRE, M., 2004.
Effect of Bt cotton on arthropod biodiversity in South
African cotton fields. Commun. agric. Appl. biol. Sci.,
69: 191-194.
JAMES, C., 2006. Preview: Global status of commercialized
biotech/GM crops: 2006. ISAAA Briefs. No. 35,
ISSAA, Ithaca, NY. http://www.isaaa.org.
JEYAKUMAR, P., TANWAR, R.K., JAT, M.C.,
DHANDAPANI, A., BAMBAWALE AND, O.M.
AND MONGA, D., 2007. Spodoptera litura: an
emerging pest on Bt cotton (Cry 1Ac) under north
Indian conditions. Pestic. Res. J., 19: 197-200.
MASCAREHANS, V.J. AND LUTTRELL, R.G., 1997.
Combined effect of sublethal exposure to cotton
expressing the endotoxin protein of Bacillus
thuringiensis and natural enemies on survival of
bollworm (Lepidoptera: Noctuidae) larvae. Environ.
Ent., 26: 939-945.
MEN, X.Y., GE, F., LIU, X.H. AND YARDIM, E.N., 2003.
Diversity of arthropod communities in transgenic Bt
cotton and nontransgenic cotton agroecosystems.
Environ. Ent., 32: 270-275.
535
MEN, X.Y., GE, F., YARDIM, E. AND PARAJULEE, M.N.,
2005. Behavioral response of Helicoverpa armigera
(Lepidoptera: Noctuidae) to cotton with and without
expression of the CrylAc delta-endotoxin protein of
Bacillus thuringiensis Berliner. J. Insect Behav., 18: 3350.
MENDELSOHN, M., KOUGH, J., VAITUZIS, Z. AND
MATTHEWS, K., 2003. Are Bt crops safe? Nature
Biotechnol., 21: 1003-1009.
NAVA-CAMBEROS, U. AND IBARRA-FRIAS, N., 2000.
Development, survival, and fecundity of the beet
armyworm on Bt and non-Bt cotton. Proceeding
Beltwide Cotton Conference, San Antonio, USA, 4-8
January, 2: 1337-1339.
PONSARD, S., GUTIERREZ, A.P. AND MILLS, N.J., 2002.
Effect of Bt-toxin (Cry1Ac) in transgenic cotton on the
adult longevity of four heteropteran predators. Environ.
Ent., 31: 1197-1205.
RAO, I.A., 2007. Why not GM crops. Available:
http://www.pakistan.com/english/advisory/biotechnolog
y/why-not.gm.crops.shtml
SHELTON, A.M., ZHAO, J.Z. AND ROUSH, R.T., 2002.
Economic, ecological, food safety, and social
consequences of the deployment of Bt transgenic plants.
Annu. Rev. Ent., 47: 845-881.
SMITH, R.H., 1997. An extension entomologist's 1996
observations of Bollgard (Bt) technology. Proceeding
Beltwide Cotton Conference, New Orleans, LA, USA,
6-10 January, 2: 856-858.
STAPEL, J.O., WATERS, D.J., RUBERSON, J.R. AND
LEWIS, W.J., 1998. Development and behavior of
Spodoptera exigua (Lepidoptera: Noctuidae) larvae in
choice tests with food substrates containing toxins of
Bacillus thuringiensis. Biol. Contr., 11: 29-37.
STEWART, S.D., ADAMCZYK, J.J., KNIGHTEN, K.S. AND
DAVIS, F.M., 2001. Impact of Bt cottons expressing
one or two insecticidal proteins of Bacillus
thuringiensis Berliner on growth and survival of noctuid
(Lepidoptera) larvae. J. econ. Ent., 94: 752-760.
WAN, P., WU, K., HUANG, M., YU, D. AND WU, J., 2008.
Population dynamics of Spodoptera litura (Lepidoptera:
Noctuidae) on Bt cotton in the Yangtze River Valley of
China. Environ. Ent., 37: 1043-1048.
WU, K.M. AND GUO, Y.Y., 2005. The evolution of cotton
pest management practices in China. Annu. Rev. Ent.,
50: 31-52.
YOUSEFI, V.O., 2000. Agrochemical in South Africa.
Available:
http://ww.occuphealth.fi/e/info/anl/199/agro03.htm
YU, Y., KANG, X., LU, Y., LIANG, J., WANG, H., WU, J.
AND YANG, Y., 2004. Effects of the transgenic Bt
cotton on the increase in population of Spodoptera
litura Fabricius. Jiangsu J. agric. Sci., 20: 169-172.
(Received 26 July 2010, revised 3 November 2010)
536
1
M. ARSHAD AND A. SUHAIL