Contents - Faperta

Development of Resistance to Transgenic Plants 393
component of a resistance management strategy. Ploughing or fl ooding the fi elds immediately
after the crop harvest will expose the hibernating larvae or pupae to the biotic and
abiotic mortality factors. Destruction of stems or burning of stubbles of crops with insect
larvae and pupae is also helpful in reducing the carryover of insects from one season to
another (Sharma and Ortiz, 2002). The frequency of resistant individuals in a strain is not
associated with induction of diapause or emergence from diapause in early winter in pink
bollworm, P. gossypiella (Carriere et al., 2001). However, emergence from diapause in the
spring has been found to be 71% lower in three highly resistant strains than in two heterogeneous
strains from which the resistant strains were derived. Therefore, there is a need to
take into consideration the proportion of population entering diapause and the numbers
that emerge in the following season. Emergence in the spring of hybrid progeny from
crosses between the resistant and heterogeneous strains has been found to be greater than
that of the resistant strains, but did not differ from susceptible strains, showing that the
over- wintering cost was recessive to some extent.
Use of a Planting Window
Following a planting window, that is, sowing crops such that the most susceptible stage
of the crop escapes pest damage or avoids peak periods of insect abundance can also be
useful in maximizing the benefi ts of transgenic crops or prolong the life of transgenic
crops. Planting the crops with the fi rst good monsoon rains has been found to be effective
in controlling the damage by sorghum shoot fl y, Atherigona soccata (Rondani), and sorghum
midge, Stenodiplosis sorghicola (Coquillett) (Sharma, 1993; Sharma and Ortiz, 2002).
Similar strategies can be employed to avoid insect damage in other crops to prolong the
effectiveness of transgenic crops.
Crop Rotations
Crops with Bt gene can be rotated with non-Bt crops in the following season or year. This
strategy would work better if Bt resistance in insect populations is not stable and breaks
down when selection pressure is removed. This strategy will also be useful in situations
where the resistance has a fi tness cost.
Integrated Pest Management
Integration of different control measures, including biocontrol agents and insecticides, as
components of pest management is important for resistance management strategy
(Australian Cotton Growers Research Association, 2001). Developing knowledge-based
strategies such as resistance management aimed at achieving long life of transgenic crops
should be commensurate with the integrated crop management (Tuli et al., 2000; Sharma
and Ortiz, 2000; Pilcher et al., 2002; Shelton, Zhao, and Roush, 2002).
Simulation Models for Resistance Management
The effects of transgenic plants on the populations of insect pests will be similar to those
of conventional host plant resistance to insects (Knipling, 1979). Effects of population