By HC Sharma and MK Dhillon

1. Biosafety of Transgenic Crops to Natural Enemies of Cotton
Bollworm/Legume Pod Borer, Helicoverpa armigera
Nov 2009
HC Sharma and MK Dhillon
International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India
To ensure sustainable deployment of transgenic insect-resistant plants, it is important that
they are compatible with other control methods, including the natural enemies (Sharma
and Ortiz 2000). Therefore, we studied the effects of transgenic cotton expressing Bacillus
thuringiensis (Bt) toxin proteins on the parasitization of Helicoverpa armigera (inset: Plate
1a) under field conditions, and the effects of Bt-transgenic cotton and Bt Cry toxin proteins
on the host specific parasitoid, Campoletis chlorideae (Plate 1a), and the generalist
predator, Cheilomemes sexmaculatus (Plate 1c) under laboratory conditions through
intoxicated H. armigera larvae, and the cotton aphid, Aphis gossypii (Plate 1b).
Effect of Bt intoxicated H. armigera larvae on the predator,
Cheilomenes sexmaculatus
The developmental period of• C. sexmaculatus fed on H. armigera larvae reared on Bt
intoxicated diet increased by 1.5 days (Fig. 2a, b). However, there was no effect on adult
emergence (Fig. 2a).
Moderate levels of• Bt protein were detected in C. sexmaculatus larvae when fed on H.
armigera larvae raised on Bt intoxicated artificial diet.
Materials and Methods
Egg, larval, and pupal parasitism of• H. armigera was monitored in Bt-transgenic and
non-transgenic cottons in the farmers’ fields in three locations in India.
Data were recorded on egg, larval, and pupal parasitization.•
To assess the effects of• Bt toxins on the host specific parasitoid, C. chlorideae, the H.
armigera larvae were reared on Bt-transgenic and non-transgenic cottons.
In another experiment, neonate larvae of• H. armigera reared on artificial diet with
commercial formulation of Bt (0.05%) and untreated control diet were offered to the
grubs of the coccinellid predator, C. sexmaculatus.
To assess the effects of• Bt-transgenic cotton on the predatory coccinellid, larvae of C.
sexmaculatus were reared on A. gossypii fed on Bt-transgenic and the non-transgenic
cottons (Mech 12 and RCH 2).
Results and Discussion
Influence of Bt-transgenic cottons on parasitization of
Helicoverpa armigera
In the farmer’s fields, egg parasitism by• Trichogramma spp. was greater on Bt-
transgenic than in non-transgenic cottons (Fig. 1a).
No differences were observed in larval parasitism by• C. chlorideae and Eriborus spp, but
no larval-pupal tachinid parasitoids were recorded in Bt cotton.
Cocoon formation in• C. chlorideae reared on H. armigera fed on Bt-transgenic cottons
was significantly lower than on non-transgenic cotton (Fig. 1b).
No• Bt toxin was detected in cocoons of the parasitoid. Reduction in cocoon formation
was due to early mortality of H. armigera rather than the direct effects of Bt toxin on the
parasitoid.
Plate 1. Ichneumonid, Campoletis chlorideae parasitizing Helicoverpa armigera larva (1a), cotton aphid,
Aphis gossypii (1b), and the coccinellid, Cheilomenes sexmaculatus (1c).
Fig. 1. Parasitization of Helicoverpa on transgenic and non-transgenic cottons in farmer’s fields (1a),
and effect of Bt-transgenic cotton on cocoon formation of larval parasitoid, Campoletis chlorideae
(1b). ++ Helicoverpa larvae fed on transgenic cottons before and after parasitization. -- Helicoverpa
larvae fed on non-transgenic cottons.
Fig. 4. Detection of Bt toxins in different
stages of Cheilomenes sexmaculatus and
Aphis gossypii.
Fig. 3. Development period (3a) and adult emergence
(3b) of Cheilomenes sexmaculatus reared on Bt-transgenic
and non-transgenic cotton fed Aphis gossypii.
Effect of Bt-transgenic cotton reared Aphis gossypii on
Cheilomenes sexmaculatus
Development period of• C. sexmaculatus reared on Bt-transgenic cotton fed A. gossypii
increased by 1 to 1.5 days (Fig. 3a), and the adult emergence decreased by 13 to 40%
(Fig. 3b).
ELISA test detected low levels (• <0.5 ppb) of Bt protein in A. gossypii and C.
sexmaculatus adults, and moderate levels (>2.5 ppb) in C. sexmaculatus larvae (Fig. 4).
Fig. 2. Development period and adult emergence of Cheilomenes sexmaculatus fed on Helicoverpa
armigera larvae reared on Bt intoxicated and untreated artificial diet.
Conclusions
There were no significant effects of transgenic crops on the activity and abundance•
of natural enemies (Sharma and Ortiz 2000). However, Bt-transgenic crops result in
decreased survival of the host-specific parasitoids.
Effects are largely due to early mortality of the insect host or its poor nutritional quality,•
rather than direct effects of Bt toxins on the natural enemies.
However, adverse effects of• Bt-transgenic crops on the natural enemies are far lower
than those of the synthetic pesticides, which result in complete elimination of the natural
enemies (Sharma et al. 2007).
References
Sharma HC, Arora R and Pampapathy G. 2007. Influence of transgenic cottons with
Bacillus thuringiensis Cry1Ac gene on the natural enemies of Helicoverpa armigera.
BioControl 52: 469-489.
Sharma HC and Ortiz R. 2000. Transgenics, pest management, and the environment.
Current Science 80: 1495-1508.
Acknowledgments: We thank the Indo-Swiss Collaboration on Biotechnology (ISCB),
Berne, Switzerland, and the Department of Biotechnology (DBT), New Delhi, India, for
financial support.
For More information write to: *HC Sharma, Principal Scientist - Entomology, email: h.sharma@cgiar.org
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