Selection of Bacillus
thuringiensis Strains Toxic Against Cotton Aphid, Aphis gossypii
Glover (Hemiptera: Aphididae)
Viviane M. Melatti, Lílian B.
Praça, Érica S. Martins, Edison
Sujii, Colin Berry, Rose G. Monnerat
Abstract
The applied biological control
of the cotton aphid, Aphis gossypii,
using Bacillus thuringiensis
is
a viable alternative. It was, recently, demonstrated that
this bacterium
can circulate inside the plant in a systemic way allowing its
utilization in
the control of sucker insects. This work aimed to establish a
methodology for
selective bioassay of B. thuringiensis
against A. gossypii and select
toxic
strains for the control of this insect.
An initial bioassay was conducted using a B.
thuringiensis strain
marked with the gene gfp
(“green
fluorescence protein”), that allowed the
visualization by fluorescence
microscopy of the bacteria in a macerate of the insects after feeding
on plants
treated with the bacteria, thus confirming the exposure of the insect
to this
control agent. Four hundred strains of B.
thuringiensis belonging to the Collection of Bacillus spp. from Embrapa Genetic Resources and
Biotechnology were tested through this bioassay method and five of them
(S29,
S40, S616, S1168, and S1576) caused
mortality above 50%. From these, S29 strain
showed the highest toxicity. The results found in this work demonstrate the
efficiency of the methodology, since the toxicity of B.
thuringiensis was confirmed against the cotton aphid, when
applied to cut stems of cotton plants.
Key
words
- Selective bioassay, biological control, entomopathogenic bacterium and
cotton crop.
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