Contents - Faperta

218 Biotechnological Approaches for Pest Management and Ecological Sustainability
In China, the transgenic cotton lines S 545, S 591, S 636, and S 1001 from Simian 3, and Zh
1109 from Zhongmiansuo 12 with Bt genes have shown adverse affects on survival and
development of H. armigera (Ni et al., 1996). Cotton cultivars Shiyuan 321, Zhongmiansuo
19, 3517, and 541 (transformed with Bt genes) have resulted in up to 96% mortality of cotton
bollworm, H. armigera (S.D. Guo et al., 1999). A chimeric gene, Bt29K (coding sequences of
activated Cry1Ac insecticidal protein) and an endoplasm reticulum-retarding signal peptide
(API-B) gene have been transferred into two cotton varieties in China (H.N. Guo et al.,
2003). Nine homozygous transgenic lines showed 90.0 to 99.7% mortality of H. armigera
larvae, good agronomic traits, and expression of Bt proteins at a level of 0.09 to 0.17%.
Insect resistance of homozygous lines expressing the activated chimeric cry1Ac and API-B
was better than the lines expressing cry1Ac only (H.N. Guo et al., 2003). First- to fourthinstar
larvae of H. armigera died on transgenic Bt cotton, the pupation decreased by 48.2
and 87.5%, and adult emergence by 66.7 and 100%, respectively. Egg laying decreased by
50.1 to 69.7%, and egg hatching by 80.6 to 87.8% (Cui and Xia, 1999). Feeding anther dust of
transgenic cotton to the adults decreased the number of eggs and egg hatching by 59.8 and
72.1%, respectively. Neonates of H. armigera have the ability to detect and avoid transgenic
Bt-cotton Zhong 30 and transgenic CpTi-Bt cotton, SGK 321 as compared to the nontransgenic
cotton Shiyuan 321 ( J.H. Zhang et al., 2004). The larvae consumed more food on
CpTi-Bt transgenic cotton than on Bt transgenic cotton. Fourth instars were in equal numbers
on transgenic and nontransgenic cottons, but food consumption on transgenic cotton
was lower than that on the nontransgenic cotton. In no-choice tests involving fi fth instars,
signifi cantly less time was spent on feeding on the two transgenic cottons. The neonates
selectively feed on the nontransgenic cotton or the preferred plant parts.
In India, cotton hybrids (Mech 12, Mech 162, and Mech 184) carrying the cry1Ac gene
were approved for cultivation in 2001, targeting bollworm, H. armigera, pink bollworm,
P. gossypiella, spotted bollworm, Earias vittella (F.), and the spiny bollworm, E. insulana (Boisd.)
(Mohan and Manjunath, 2002). Under integrated pest management, the transgenic cotton
hybrid Mech 162 suffered lower damage by the bollworms H. armigera and P. gossypiella
(11.5%) as compared to the conventional cotton (29.4%) (Bambawale et al., 2004). Only three
sprays were needed for pest control on the transgenic cotton compared to seven sprays on
the conventional cotton. The seed cotton yield was 12.4 q ha 1 in Mech 162 compared to
7.1 q ha 1 in the conventional cotton. There is considerable variation in the production
of Cry1Ac toxin protein in different plants of the same and different hybrids, and over the
crop-growing season, and Cry1Ac production declines during the fruiting stage (Kranthi
et al., 2005). Different Bt transgenic hybrids vary in their susceptibility to H. armigera, and
the mortality of H. armigera larvae declines substantially during the latter part of the crop
growth. The larval numbers were signifi cantly lower on the transgenic hybrids under high
infestation, but the differences in larval density between the transgenic and nontransgenic
hybrids under low levels of infestation were quite small (H.C. Sharma and Pampapathy,
2006). Bollworm damage in squares and bolls was signifi cantly lower in the transgenic
hybrids than in the nontransgenic ones, although there were a few exceptions. Differences
in seed cotton yield between the transgenic and the nontransgenic hybrids were not signifi
cant under unprotected conditions at moderate levels of infestation. However, signifi -
cant differences in seed cotton yield were observed under heavy bollworm infestation.
Transgenic hybrids also suffered low shoot damage by spotted bollworm, E. vittella.
Bollworm damage and seed cotton yield of the Gossypium arboreum L. varieties Aravinda
and MDL 2450 have been found to be similar to the transgenic hybrids, suggesting that it
would be useful to combine transgenic resistance to H. armigera with plant characteristics
conferring resistance to this pest or nontarget insect pests in the region to realize the