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4. DiscussionThe results show that tomato plants expressing thecry1Ab gene were protected against damage by H.armigera in the same manner as that described byPeferoen et al. (1990) for potato. The green house trialsshowed that H. armigera did not damage the foliage orthe fruits of transgenic plants and no adverse effectswere observed on the growth ofthe plants. Infestationby H. armigera on non-transgenic plants had an adverseeffect on their growth and the damage was so extensivethat they did not bear any fruit. Even under controlledlaboratory conditions, excised fruits from the Bt tomatoplants suffered very little damage by H. armigera larvae.Surviving larvae grew very rapidly from 2nd instar to5th instar on the non-transgenic fruits whilst on thetransgenic fruits, larval growth was very slow. Similarresults occurred on transgenic tomatoes infested with H.armigera in Belgium (Jansens et al., 1992). Rarely doesH. armigera build up its own high population from theinitial low infestations on the tomato crop. Helicoverpaarmigera emigrating from other crops can infesttomatoes in large numbers and most of the fruits sufferextensive damage by the pest. By the time farmers detectan infestation, it is usually very late and controlmeasures in the form of pesticide application areineffective. Control failure is probably because of thelack ofpest monitoring system, improper timing of thepesticide application, inappropriate insecticides andresistance against the widely used pesticides (Matthews,1993). Under such conditions, resistance imparted toplants by Bt proteins, as described above, will be highlydesirable and will provide an effective and sustainablecontrol method for H. armigera in the field.It is assumed that in a Bt tomato crop, eggs will belaid by invading H. armigera moths and that newlyemerged larvae would invade the tomato tissue to feedas there is no evidence that transgenic Bt plants inhibitthe oviposition or hatching oflepidopt erous pests(Kumar, in press). Even though, emerging larvae wouldsuffer mortality on Bt plants, they would have causedsome damage to the terminal leaves and flowers oftheplants by initial penetration and probing ofthe tissueprior to death. Therefore in order to manage H.armigera on Bt tomato or Bt cotton, the followingtactics would be required to be considered in an
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