The efficacy and sustainability of the CIMBAA transgenic Cry1B/Cry1C Bt cabbage and cauliflower plants for control of lepidopteran pests

摘要

In 2003 the Collaboration on Insect Management for Brassicas in Asia and Africa (CIMBAA) public/private partnership selected the Cry1B/Cry1C Bt protein combination as having the potential to provide effective and sustainable control of diamondback moth (DBM), Plutella xylostella. Following transformations and extensive plant selection, insect efficacy trials were undertaken in 2008 to 2010 in north India (Murthal near New Delhi) and south India (near Bengaluru) in large scale screen-house experiments using artificial infestations on the best performing (Elite Event) plant lines and on hybrids produced from them. Plant damage was scored on a scale of 0 (no visible damage) to 4 (plant effectively destroyed). For DBM, cabbage cluster caterpillar (Crocidolomia binotalis), cabbage webworm (Hellula undalis) and semi-looper (Trichoplusia ni) there was zero insect survival and a zero damage score on the Elite Event lines and on their hybrids, while control plants had 50 to 100% insect survival (depending on species, life stage and trials) and damage scores of 3.3 to 4. Cabbage white (Pieris brassicae) and common army worm (Spodoptera litura) showed some larval survival and damage scores up to 1.4 (especially in early trials) but no survival to pupation. Screening of DBM populations worldwide (inc. 18 populations for Cry1B and 13 for Cry1C from India) showed mean LC50s close to that of international susceptible strains. To date F2 screening has not identified the presence of resistance genes in DBM in the field. Cry1B resistance was slowly developed artificially in the laboratory but 1C resistance and resistance to the Cry1B/1C combination was harder to develop and had higher fitness costs. The ‘resistant’ lines showed some extended survival of stunted DBM larvae on dual gene Bt plants but no survival to pupation. There was no cross-resistance between Cry1B and Cry1C. Resistance to both genes was autosomal and recessive. Beneficial insects were demonstrated to have the potential to provide additional mortality on rare surviving insects in Bt fields. Aphids were well controlled for the first 40 days post-transplanting using imidacloprid pelleted onto seed and, if necessary, by 1-2 Verticillium lecanii sprays thereafter. Surviving S. litura and Helicoverpa armigera in Bt sprayed fields were well controlled by one or two applications