Transgenic Resistance to Heliothis/Helicoverpa:Implications for Sustainable Crop Production

Dec 2009

HC Sharma*, G Pampapathy and MK DhillonInternational Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India.

For more information, contact: HC Sharma, Principal Scientist (Entomology), e-mail: h.sharma@cgiar.org

IntroductionHeliothis/Helicoverpa are the most important crop pests worldwide, and result in crop loss of over $5 billion, despite application of insecticides costing over $2 billion annually (Plate 1). Massive application of insecticides to control these pests have resulted in adverse effects on the environment, and it is in this context that insect-resistant transgenic plants expressing toxin genes from Bacillus thuringiensis (Bt) can play a major role in pest management for sustainable crop production. Genetically modified crops were planted on over 100 million ha in 2008, and nearly one quarter of the crop area planted to transgenic crops was grown in developing countries.

Development of transgenic plants for Heliothis/Helicoverpa managementTransgenic plants with resistance to Heliothis/Helicoverpa have been developed in cotton, maize, tomato, tobacco, chickpea and pigeonpea. Transgenic cottons expressing Bt genes are effective against Helicoverpa zea, Heliothis virescens and Helicoverpa armigera. Insecticide application for bollworm control on transgenic cottons is reduced by nearly half, while the cottonseed yield increases by 25 to 45% over the non-transgenic cottons (Plate 2, Fig. 1). Transgenic plants expressing Bt genes have also been developed in chickpea and pigeonpea for controlling these pests.

Deployment of insect-resistant transgenic plants for pest managementFor effective deployment of insect-resistant transgenic plants for pest management, there is a need to insert the Bt genes into cultivars with adaptation to different agro-climatic conditions with stable gene expression. For effective deployment of transgenic plants for pest management, there is need for:

• Destroying the carryover population• Planting refugia under extensive monoculture• Effective control of secondary pests• Pyramiding genes and regulating gene expression• Use of IPM and IRM strategies from the beginning.

Advantages of transgenic crops• Significant reduction in insecticide sprays• Increased activity of natural enemies• Reduced exposure of non-target organisms to pesticides• Reduction in pesticide residues in food and food products.

Limitations of transgenic crops• Emergence of secondary pest problems• Evolution of resistance to the transgenic crops• Adverse effects on non-target organisms• Gene escape into the environment.

ConclusionsIncorporation of insecticidal genes into crop plants will have a tremendous effect on pest management. Emphasis should be placed on combining exotic genes with conventional host plant resistance, and also with traits conferring resistance to other insect pests and diseases of importance in the target region. There is a need to follow integrated pest management practices from the very beginning to make transgenic crops a viable technology for sustainable crop production.

Plate 1. Helicoverpa damage in cotton (a), chickpea (b) and pigeonpea (c).

Fig. 1. Bollworm damage (A) and seedcotton yield (B) in transgenic and non-transgenic cottons under protected conditions.

Plate 2. Performance of Bt-transgenic and non-transgenic cottons for controlling bollworms under protected and unprotected conditions.

Bt Mech 12: Protected Bt Mech 12: Unprotected

Non Bt Mech 12: Protected Non Bt Mech 12: Unprotected

(a) (c)

(b)

A B