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Title of Thesis
Impact of BT and Non_BT Cotton Insect Biodiversity

Muhammad Arshad
Institute/University/Department Details
University of Agriculture, Faisalabad,  Pakistan
Agricultural Entomology
Number of Pages
Keywords (Extracted from title, table of contents and abstract of thesis)
insect pests, transgenic Bt cotton, Helicoverpa armigera, Spodoptera exigua.

The undertaken project “Impact of Bt and non-Bt cotton on insect biodiversity” was carried out for two cotton seasons, 2006-07, which included the survey and experimentations. The survey study was conducted to know the farmers’ perception of insect pests and pest management practices in Bt cotton. The experimentations were consisted the field and laboratory experiments. The field experiments were conducted to determine the impact of transgenic Bt cotton on the target and non-target insect community in replicated field trails under sprayed and unsprayed conditions, in comparisons with its parent non-Bt conventional cotton. The laboratory experiments were conducted to evaluate the impact of Bt toxin on the biological traits (larval mortality, larval development time and pupal weight) of Helicoverpa armigera and Spodoptera exigua by feeding larvae on the leaves and flower-bolls of Bt and non-Bt cotton. The results revealed that transgenic Bt cotton (IR-FH-901), containing Cry1Ac proved to be highly effective against specific lepidopterous pests and the susceptibility of target pests was in the order of american bollworm> spotted bollworm> pink bollworm >armyworm. The pooled data of all observations showed significantly lower population of bollworm complex (american, spotted and pink bollworms) in Bt cotton. Bt cotton proved not to be so effective against armyworm but some sub-lethal effects have been observed in term of increased larval development time and reduction in pupal weight. It was not effective against sucking insect pests and average 3-4 insecticide applications were used to control these pests in sprayed plots of Bt and non-Bt cotton. The diversities of non-target insect community and sub communities (pests, beneficials, pollinators and visitors) as measured by Shannon-Weaver diversity index showed no significant differences in species abundance, richness, diversity and evenness in the unsprayed Bt and non-Bt cotton during two successive years. But the differences were found between sprayed and unsprayed plots. The higher diversity indices in insecticide treated plots suggest that insecticide sprays had a significant impact in eliminating the rare species and hence increased the diversity due to higher evenness among the species. The reduced insecticide use in Bt cotton increased the stability of rare species and have a positive impact on beneficial insect community. The seed treatment in transgenic Bt cotton proved to be very effective in controlling sucking insect pests complex during early stages of crop. Although, Bt cotton significantly reduced the use of insecticides against bollworms, but farmers still relied heavily on the chemicals to control these pests, as they were not sure of its effectiveness against target pests, because, they were easily convinced by the commercial advertisements of pesticide companies. The results revealed that the judicious use of insecticides in Bt cotton at economic threshold level was provided the salubrious conditions for beneficial insects conservation. The efficacy of Bt insecticidal protein in different plant parts was in the order of leaves>flower-bolls. The increased larval population in Bt cotton at later stages of crop indicated spatial and temporal variation of Cry1Ac toxin expression. The studies highlight that researchers, technology providers and administrators should ensure the effective and highest level of Bt toxin expression in appropriate plant parts at the requisite time, particularly late in the season.

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1062 KB

S. No. Chapter Title of the Chapters Page Size (KB)
1 1 Introduction 1

32 KB

2 2 Review of Literature 7


551 KB

  2.1 Transgenic Bt cotton 7
  2.2 Transgenic Bt cotton and insecticide use 9
  2.3 Farmers’ knowledge and perception of Bt cotton 10
  2.4 Impact of transgenic Bt cotton on target insect pests 11
  2.5 Impact of transgenic Bt cotton on non-target insect pests 13
  2.6 Impact of transgenic Bt cotton on the biology (survival and growth) of cotton boll (Helicoverpa armigera) and armyworms (Spodoptera exigua)….. 17
3 3 Materials and Methods 20

86 KB

  3.1 Survey study 20
  3.2 Experimentation 21
  3.3 Statistical analysis 28
4 4 Results 32

345 KB

  4.1 Survey study 32
  4.2 Field experiments 46
  4.3 Laboratory experiments 110
5 5 Discussion 115
92 KB
  5.1 Survey study 115
  5.2 Field experiments 119
  5.3 Laboratory experiments 128
6 6 Summary and Conclusion 131
79 KB
  6.1 Survey study 131
  6.2 Experimentation 132
    Literature Cited 137
118 KB