Studies on Resistance to Vegetative (Vip3A) and Crystal (Cry1A) Insecticidal Toxins of Bacillus thuringiensis in Heliothis virescens (Fabricius)
Author(s)
Pickett, Brian R
Type
Thesis
Abstract
Bacillus thuringiensis (Bt) toxins expressed in commercial transgenic crop varieties
are all δ-endotoxins (Cry toxins) but the identification of novel vegetative insecticidal
proteins (Vip toxins) has extended the range of insecticidal proteins derived from Bt.
One such Vip toxin, Vip3A, primarily targets the midgut epithelium cells of
susceptible insects as Cry toxins do, although they appear to have different binding
sites. The present study investigated the comparative toxicity of Vip3A, Cry1Ab and
Cry1Ac against Heliothis virescens (tobacco budworm) and the impact of antibiotics
on Bt insecticidal activity. The selection of a resistant Vip3A population led to the
determination of cross-resistance, the genetics of resistance and fitness effects. There
was very little variability in the natural susceptibility to Vip3A, Cry1Ab and Cry1Ac
in the populations tested, although the toxicity of Vip3A was much lower compared to
the Cry1A toxins. A Vip3A resistant population was successfully established within
13 selected generations, with little or no cross-resistance to Cry1Ab or Cry1Ac. The
inheritance of resistance ranged from almost completely recessive to incompletely
dominant with a possible paternal influence, was polygenic and relatively stable.
Vip3A resistance showed a fitness benefit, reduced larval development time, and
fitness costs, including survival to adult eclosion, reduced egg viability and reduced
male mating success. The effects of antibiotics on H. virescens larval susceptibility to
Bt toxins varied depending on antibiotic treatment, the Bt toxin used and the larval
instar tested. Bt cotton expressing both Vip3A and Cry1Ab to provide activity against
a wide range of pest Lepidoptera, including H. virescens, a major cotton pest in the
USA is in the process of commercialisation. The present work will help to support a
suitable insecticide resistance management strategy for continued use of Bt toxin in
transgenic crops.
are all δ-endotoxins (Cry toxins) but the identification of novel vegetative insecticidal
proteins (Vip toxins) has extended the range of insecticidal proteins derived from Bt.
One such Vip toxin, Vip3A, primarily targets the midgut epithelium cells of
susceptible insects as Cry toxins do, although they appear to have different binding
sites. The present study investigated the comparative toxicity of Vip3A, Cry1Ab and
Cry1Ac against Heliothis virescens (tobacco budworm) and the impact of antibiotics
on Bt insecticidal activity. The selection of a resistant Vip3A population led to the
determination of cross-resistance, the genetics of resistance and fitness effects. There
was very little variability in the natural susceptibility to Vip3A, Cry1Ab and Cry1Ac
in the populations tested, although the toxicity of Vip3A was much lower compared to
the Cry1A toxins. A Vip3A resistant population was successfully established within
13 selected generations, with little or no cross-resistance to Cry1Ab or Cry1Ac. The
inheritance of resistance ranged from almost completely recessive to incompletely
dominant with a possible paternal influence, was polygenic and relatively stable.
Vip3A resistance showed a fitness benefit, reduced larval development time, and
fitness costs, including survival to adult eclosion, reduced egg viability and reduced
male mating success. The effects of antibiotics on H. virescens larval susceptibility to
Bt toxins varied depending on antibiotic treatment, the Bt toxin used and the larval
instar tested. Bt cotton expressing both Vip3A and Cry1Ab to provide activity against
a wide range of pest Lepidoptera, including H. virescens, a major cotton pest in the
USA is in the process of commercialisation. The present work will help to support a
suitable insecticide resistance management strategy for continued use of Bt toxin in
transgenic crops.
Date Issued
2009-06
Date Awarded
2009-12
Advisor
Wright, Denis
Creator
Pickett, Brian R
Publisher Department
Biology
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)