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Host plant influences the biological activity of Bacillus thuringiensis towards Helicoverpa armigera
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Host plant influences the biological activity of Bacillus thuringiensis towards Helicoverpa armigera

  1. Helicoverpa armigera is an important pest of cotton, grain legumes, cereals, vegetables, fruits, and forest trees (Plate 1). Toxin genes from the bacterium, Bacillus thuringiensis (Bt) have been deployed in genetically modified plants for controlling insect pests. However, genotypic resistance excercises considerable influence on the efficacy of Bt genes expressed in transgenic plants for pest management (Sharma and Pampapathy 2006). Therefore, we studied the bioefficacy of Bt against H. armigera involving chickpea, pigeonpea, sorghum, and cotton genotypes with different levels of resistance/susceptibility to this insect. Materials and Methods Interactions of Bt with different genotypes of chickpea, pigeonpea, sorghum, and cotton were studied by incorporating the freeze-dried powder of terminal branches of chickpea (ICCC 37-S and ICC 506-R), tender green pods of pigeonpea (ICPL 87-S and ICPL 332-R), dough-stage sorghum grain (IS 18698-high tannins and ICSV 745-low tannins), and squares of cotton (Bt and Non-Bt RCH 2) into the artificial diet with and without Bt. Freeze-dried powder (20 g) of leaves, pods, grains, or squares (replacement for part of chickpea flour in the artificial diet) was mixed with ingredients sufficient for 300 ml artificial diet for rearing H. armigera (Armes et al. 1992). Data were recorded on larval and pupal periods and weights, pupation and adult emergence. Fecundity was recorded in five pairs of adults emerging in each treatment. Results and Discussion Survival and development Larval weight at 10 days after initiating (DAI) the experiment was lowest (0.1 mg) in the larvae reared on diets with square powder of Bt-transgenic cotton, RCH 2 + Bt, followed by the larvae reared on the diets with square powder of Bt-transgenic cotton, RCH 2 without the Bt (0.9 mg) (Fig. 1). Lowest pupal weight (284.0 mg) was recorded in insects reared on diets with grain flour of sorghum genotype, ICSV 745. Pupal weights of the insects reared on diets with leaf powder of chickpea and pod powder of pigeonpea were similar to those reared on standard artificial diet. Larval period was shortest on diets without Bt (18.8 days) as compared to that on diets with Bt (21.6 days). Larval period was prolonged in insects reared on diets with ICPL 332 pod powder + Bt (30.0 days) as compared to the insects reared on diets with ICC 506 leaf powder (15.8 days) (Fig. 2). Plate 1: Helicoverpa armigera damage in chickpea, cotton, pigeonpea, and sorghum. 0 50 100 150 200 250 300 ICCC 37 ICC 506 ICPL 87 ICPL 332 IS 18698 ICSV 745 NBt RCH 2 Bt RCH 2 Control Chickpea Pigeonpea Sorghum Cotton Without Bt With Bt Larvalweight(10DAI)(mg) Fig. 1: Effect of lyophilized chickpea leaf, pigeonpea pod, sorghum grain, and cotton square powders along with Bt (0.0125%) on weights of Helicoverpa armigera larvae. Pupation and adult emergence Percentage pupation was lower in insects reared on diets with ICC 506 leaf powder + Bt (40.0 %), ICSV 745 grain powder + Bt (33.3 %), and ICPL 332 pod powder + Bt (13.3 %) as compared to the insects reared on diets with ICC 506 leaf powder (53.3 %), ICSV 745 grain powder (43.3 %) and ICPL 332 pod powder (46.7 %). Adult emergence was lowest in insects reared on the diets with ICC 506 leaf powder + Bt (13.3 %), followed by those reared on standard artificial diet with Bt (18.9 %), and ICPL 332 pod powder + Bt (33.3 %) (Fig. 3). Larvae reared on diets with square powder of cotton (with or without Bt) did not survive to pupal stage. This may be because of the action of Bt and the secondary plant metabolites such as gossypol, tannins, and anthocyanins present in cotton (Sharma and Agarwal 1982). Adult longevity and fecundity Longevity of adults was shorter in insects reared on artificial diets with Bt as compared to the insects reared on artificial diets without Bt. No eggs were laid by the insects reared on the diets with Bt, except the insects reared on diets with ICCC 37 leaf powder + Bt (153.3 eggs female-1 ), and the standard artificial diet with Bt (58.3 eggs female-1 ) (Fig. 4). 0 10 20 30 40 ICCC 37 ICC 506 ICPL 87 ICPL 332 IS 18698 ICSV 745 NBt RCH 2 Bt RCH2 Control Larvalperiod(Days) Chickpea Pigeonpea Sorghum Cotton Without Bt With Bt Fig. 2: Effect of lyophilized chickpea leaf, pigeonpea pod, sorghum grain, and cotton square powders along with Bt on the larval period of Helicoverpa armigera. ICC 506 ICPL 87 ICPL 332 IS 18698 ICSV 745 NBt RCH 2 Bt RCH 2 Control Adultemergence(%) Chickpea Pigeonpea Sorghum Cotton 0 20 40 60 80 100 ICCC 37 Without Bt With Bt 0 100 200 300 400 ICCC 37 ICC 506 ICPL 87 ICPL 332 IS 18698 ICSV 745 NBt RCH Bt RCH 2 Control Chickpea Pigeonpea Sorghum Cotton With BtWithout Bt Fecundity(eggsfemale-1 ) Fig. 3 & 4: Effect of lyophilized chickpea leaf, pigeonpea pod, sorghum grain, and cotton square powders along with Bt on adult emergence and fecundity of Helicoverpa armigera. Conclusions • Survival, development, and fecundity of H. armigera were poor with diets containing lyophilized tissue of insect-resistant genotypes and Bt as compared to that on the susceptible genotypes. • The δ-endotoxin genes of Bt can be deployed more effectively in crop plants with inherent resistance to insects for sustainable crop production. References Armes NJ, Bond GS and Cooters RJ. 1992. The Laboratory Culture and Development of Helicoverpa armigera. Bulletin No. 57. Chatham, UK: Natural Resources Institute. Sharma HC and Agarwal RA. 1982. Effect of some antibiotic compounds in Gossypium on the post-embryonic development of spotted boll worm (Earias vittella F.). Entomologia Experimentalis et Applicata 31:225-228. Sharma HC and Pampapathy G. 2006. Influence of transgenic cottons on the relative abundance and damage by target and non-target insect pests under different protection regimes in India. Crop Protection 25: 800-813. For more information contact: HC Sharma, Principal Scientist (Entomology) ICRISAT, Patancheru 502 324, Andhra Pradesh, India. Email: H.Sharma@cgiar.org 1 International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India 2 Acharya N.G. Ranga Agricultural University, Agricultural College, Bapatla, Andhra Pradesh, India. Nov 2009 I Paramasiva1,2 , HC Sharma1* and PV Krishnayya2 Host plant influences the biological activity of Bacillus thuringiensis towards Helicoverpa armigera
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