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 MethodsEgg, 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 DiscussionInfluence 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.

ConclusionsThere 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).

ReferencesSharma 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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