Contents - Faperta

340 Biotechnological Approaches for Pest Management and Ecological Sustainability
secondary plant metabolites, vegetative insecticidal proteins, and small RNA viruses can
also be deployed through the transgenic plants alone or in combination with Bt genes for
crop protection (Sharma et al., 2000; Sharma and Pampapathy, 2006).
Introduction of transgenic crops will lead to an increase in crop productivity, and result
in preservation of natural habitats because less land may be used for agriculture. A number
of ecological and economic issues need to be addressed while considering the production
and deployment of transgenic crops for insect control (Sharma and Ortiz, 2000). The most
important consideration is the immediate reduction in the amount of pesticides applied
for pest control. The number of pesticide applications on a crop such as cotton varies from
10 to 25, and most of the sprays are directed against key pests such as Heliothis virescens F.,
Helicoverpa zea (Boddie), and H. armigera (Hubner). In situations where transgenic crops are
introduced as a component of pest management, the number of pesticide sprays is likely to
be reduced by two third to half. Reduction in number of pesticide sprays would lead to
increased activity of natural enemies, while some of the minor pests may tend to attain
higher pest densities in the absence of sprays applied for the control of major pests, for
example, plant hoppers, Amrasca biguttula biguttula Ishida, and stink bug, Nezara viridula
(L.), on Bt-cotton (Bundy, McPherson, and Herzog, 2000; Sharma and Pampapathy, 2006).
The deployment of insect-resistant transgenic plants for increasing the production and
productivity of crops for sustainable crop production has raised some concerns about the
real or conjectural effects of transgenic plants on nontarget organisms, including human
beings (Miller and Flamm, 1993; Sharma et al., 2002), and evolution of resistant strains of
insects (Williamson, Perrins, and Fitter, 1990). As a result, the caution has given rise to
doubt because of lack of adequate information. However, genetically modifi ed organisms
have a better predictability of gene expression than conventional breeding methods, and
transgenes are not conceptually different than the use of native genes or organisms modifi
ed by conventional technologies. Historically, crop plants have not been subjected to risk
or safety analysis or risk management, and are improved by cross-pollination between
plants with desirable traits, or with species that are sexually compatible.
Effi cacy of transgenic crops for controlling the target and the nontarget pests, and their
effects on natural enemies need to be determined on a regional basis. The signifi cance of
such effects would depend on the importance of the immature stages of the target insect
for maintaining the populations of the natural enemies. Transgenic plants may reduce the
numbers of certain natural enemies in areas planted with transgenic crops, but their populations
may be maintained on the other crops that serve as a host to the target pests. A few
of the known predators are specialists on one insect and hence, the populations of the
predators and parasitoids with a wide host range would be maintained on other insect
species (Fitt, Mares, and Llewellyn, 1994; Jasinski et al., 2001; Dhillon and Sharma, 2007).
Within-fi eld impact may be greater for parasitoids that are monophagous, and populations
of such natural enemies can only be maintained on the nontransgenic crops or other hosts
of the target pest. Finally, the effects of transgenic crops on the abundance of natural enemies
should be compared with the nontransgenic fi elds of the same crop where the natural
enemies may be virtually absent because of heavy pesticide application.
Transgenic plants released for commercial use must contain information on environmental
safety assessment. To generate such information, studies need to be conducted
under laboratory and fi eld conditions, following standard ecotoxicological procedures
used for insecticides. Ecotoxicological studies on insecticides are designed based on their
mode of action, mode of application (foliar sprays drift to neighboring plants and also
affect nontarget organisms), and their presence (residues) in the environment (for a limited
period of time due to rapid degradation). However, such studies may be insuffi cient to