Contents - Faperta

324 Biotechnological Approaches for Pest Management and Ecological Sustainability
under diverse environmental conditions to assess their role in IPM programs. Long-term
suppression of pest populations would be governed by insect-host plant interactions,
reproductive rate, dispersal propensity, and regional abundance of the transgenic crops
(Carriere et al., 2003). Pink bollworm, P. gossypiella, population density has declined considerably
in regions where Bt cotton was abundant. Such long-term suppression has not
been observed with Bt sprays, indicating that transgenic crops have opened up new avenues
for pest management.
Deployment of insect-resistant transgenic crops will lead either to an increase in the
economic threshold level (ETL) or delay the time required by the insects to reach the ETL,
depending on the nature of resistance and the stage of the insect on which the ETL is
based. Crop growth and pest incidence should be monitored carefully so that appropriate
control measures are initiated in time based on ETLs. Care should be taken to use alternate
control options such as natural enemies, biopesticides [nucleopolyhedrosis viruses (NPV),
entomopathogenic fungi, and nematodes], and natural plant products (neem, custard
apple, and Pongamia), which do not disturb the natural control agents. Use of pesticide
formulations such as seed treatment with systemic insecticides or soil application of granules
of systemic insecticides to control sucking pests early in the season, and spraying
selective insecticides may be considered to suppress insect populations in the beginning
of the season to minimize adverse effects on the natural enemies (Sharma and Ortiz, 2000;
Sharma et al., 2002b). Broad-spectrum and toxic insecticides should be used only during
the peak activity periods of the target or nontarget pests. Efforts should be made to rotate
pesticides with different modes of action, and avoid repetition of insecticides belonging to
the same group or insecticides that fail to give effective control of the target insects.
Deployment of transgenic plants should be based on the overall philosophy of IPM, taking
into account alternate mortality factors, reduction of selection pressure, and monitoring
populations for resistance development to design more effective management strategies.
To increase the effectiveness and usefulness of transgenic plants, it is important to develop
a strategy to prolong the life and effectiveness of transgenic crops for pest management
(Sharma et al., 2002b).
It is important to implement IPM strategies from the very beginning to increase the
effectiveness and prolong the life of the transgenic crops. However, in the absence of
effective alternatives, farmers continue to rely heavily on insecticides. Once commercialized,
the insect-resistant transgenic crops should be able to fulfi ll this need. While Bt
cotton can largely control the bollworm complex, sucking pests and other nonlepidopteran
insects will have to be tackled by combining host plant resistance (HPR) and biological,
cultural, and chemical control methods. Transgenic crops cannot be effective as a standalone
technology to manage insect pests, but can serve as one of the options in IPM.
Combining various IPM strategies may be effective in delaying development of resistance
to the transgene in pest populations. The IPM systems should diversify the mortality factors
so that resistant strains are not selected for a single mortality mechanism, and thus,
reduce the selection pressure on the pest populations for any single mortality factor. The
following approaches may be followed for increasing the effectiveness of transgenic crops
for pest management.
Transgenic Crops and Chemical Control
Transgenic crops can make a critical contribution in reducing the dosage and frequency of
insecticide application. For rational pest management, transgenic cultivars have to be
deployed in combination with low dosages of insecticides (Schell, 1997). Transgenic cotton