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Title of Thesis
Impact of BT and Non_BT Cotton Insect Biodiversity |
Author(s)
Muhammad Arshad |
Institute/University/Department Details
University of Agriculture, Faisalabad, Pakistan |
Session
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Subject
Agricultural Entomology |
Number of Pages
188 |
Keywords (Extracted from title, table of contents and abstract of thesis)
insect pests, transgenic Bt cotton, Helicoverpa armigera, Spodoptera
exigua. |
Abstract
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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