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1International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India2Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, 8046, Zürich, Switzerland.
Nov 2009
MK Dhillon1, HC Sharma1 and J Romeis2
Chickpea Mediated Effects of Bacillus thuringiensisCry Toxins on Survival of Helicoverpa armigera and
its Larval Parasitoid, Campoletis chlorideae
The noctuid pod borer, Helicoverpa armigera (Plate 1a) is the most important pest of field crops, including chickpea in Asia, Africa and Australia. Genes from the bacterium, Bacillus thuringiensis (Bt) have been deployed successfully through transgenic crops on a commercial scale. In general, there are no serious effects of Bt transgenic crops on the generalist predators. However, parasitoid activity is affected when their insect hosts are affected by the Bt toxins in transgenic plants (Romeis et al. 2006; Sharma et al. 2008). To ensure a sustainable deployment of transgenic insect-resistant plants, it is important that they are compatible with natural enemies of crop pests. Therefore, we studied the effects of Bt toxins on the H. armigera larval parasitoid, Campoletis chlorideae (Plate 1b) through Bt intoxicated larvae on chickpea.
Materials and methodsHost plant mediated effects of chickpea genotypes (ICC 506 – resistant, ICCV 10 - moderately resistant, C 235 – moderately susceptible, and L 550 – susceptible) and the commercial Bt formulation (BiolepR) were studied on the H. armigera larval parasitoid, C. chlorideae under field conditions. Chickpea genotypes planted in the field were sprayed with Bt (0.05%) at the flowering stage. Terminal branches from sprayed plots were fed to neonate H. armigera larvae using the detached leaf assay technique (Sharma et al. 2005). Helicoverpa armigera larvae were exposed to the C. chlorideae females for parasitization, after 5 days of feeding on terminal braches in Bt sprayed, and after 3 days on untreated controls. Observations on survival of H. armigera and the C. chlorideae under different treatment conditions were recorded. Survival and fecundity of C. chlorideae was also studied in the next generation without Bt to assess carryover effects, if any. Helicoverpa armigera larvae, and the larvae, pupae, and adults of C. chlorideae were subjected to ELISA (Agdia, Inc., USA) for detection of Bt-toxins.
Results and Discussion
Chickpea mediated effects of Bt on the survival of Helicoverpa armigera and its parasitoid, Campoletis chlorideaeSurvival of H. armigera larvae was significantly greater on the susceptible - L 550 than that on the resistant - ICC 506 under unsprayed conditions, while the reverse was true under Bt treated conditions, suggesting that Bt sprays were relatively less effective on the Helicoverpa-resistant genotype, ICC 506 (Fig. 1a). Bt sprays significantly reduced cocoon formation (44.2 to 75.0%) of C. chlorideae over the untreated controls (Fig 1b). Bt proteins result in reduced cocoon formation and adult emergence of C. chlorideae, and prolong the larval period of the parasitoid raised on Bt intoxicated larvae of H. armigera (Sharma et al. 2008). Resistance or susceptibility of the chickpea genotypes to H. armigera did not have a significant affect on cocoon formation of C. chlorideae, suggesting that Helicoverpa-resistant chickpea genotypes are compatible with C. chlorideae. Adverse effects of Bt toxins on C. chlorideae are mainly because of early mortality of Bt-fed H. armigera larvae, and slow growth and poor quality of the insect host (Sharma et al. 2007).
Carryover effects of Bt on Campoletis chlorideaeThere were no significant carryover effects of Bt on survival (Fig. 2a) and fecundity (Fig. 2b) ofC. chlorideae in the next generation. Cocoon formation was significantly greater on H. armigera larvae reared on ICCV 10 and C 235 than on ICC 506 and L 550, suggesting that chickpea genotypes have indirect effects on the parasitoid through poor survival and development of H. armigera.
Plate 1. Pod borer, Helicoverpa armigera damage in chickpea (1a), and parasitization of the larvae by the parasitoid, Campoletis chlorideae (1b).
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Fig. 1. Survival of Helicoverpa armigera larvae (1a), and cocoon formation of the parasitoid, Campoletis chlorideae (1b) on Bt treated and untreated plants of four chickpea genotypes.
Detection of Bt in Helicoverpa armigera and its parasitoid, Campoletis chlorideaeThe ELISA test detected Bt proteins in the H. armigera larvae fed on Bt treated chickpea plants. No Bt proteins were detected in the larvae, cocoons and adults of C. chlorideae reared on Bt intoxicatedH. armigera larvae (Fig. 3).
Conclusions• Although H. armigera larvae fed on Bt treated chickpeas showed adverse effects on
C. chlorideae, these effects were largely host-mediated, since no Bt protein was detected in the parasitoid, C. chlorideae.
• Deployment of Bt-transgenic chickpeas may result in some density-dependent effects on the abundance of C. chlorideae, but such effects may be far lower than those of synthetic insecticides used for controlling this pest.
ReferencesRomeis J, Meissle M and Bigler F. 2006. Transgenic crops expressing Bacillus thuringiensis toxins and biological control. Nature Biotechnology 24: 63-71.Sharma HC, Dhillon MK and Arora R. 2008. Effects of Bacillus thuringiensis δ-endotoxin fed Helicoverpa armigera (Hübner) on the survival and development of the parasitoid, Campoletis chlorideae Uchida. Entomologia Experimentalis et Applicata 126: 1-8.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, Pampapathy G, Dhillon MK and Ridsdill-Smith TJ. 2005. Detached leaf assay to screen chickpeas for resistance to pod borer, Helicoverpa armigera. Journal of Economic Entomology 98: 568-576.
Acknowledgements: We thank the Indo-Swiss Collaboration on Biotechnology (ISCB), Swiss Agency for Development and Cooperation (SDC), 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: [email protected]
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Fig. 2. Carryover effects of Bt on the survival (2a) and fecundity (2b) of Helicoverpa armigera larval parasitoid, Campoletis chlorideae in the second generation.
Fig. 3. Detection of Bt proteins in larvae of Helicoverpa armigera, and larvae, pupae, and adults of Campoletis chlorideae reared on H. armigera fed on the Bt sprayed and unsprayed chickpeas. Cells 1 to 4: H. armigera larvae fed on Bt sprayed chickpeas; cells 5 to 8:H. armigera larvae fed on untreated chickpeas; cells 9 to 12, 17 to 20, and 25 to 28:C. chlorideae larvae, cocoons, and adults obtained from H. armigera larvae fed on Bt sprayed chickpeas; cells 13 to 16, 21 to 24, and 29 to 32: C. chlorideae larvae, cocoons, and adults obtained from H. armigera larvae fed on untreated chickpeas; cell 33: blank; cell 34: negative control; and cell 35: positive control.
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