Environmental Engineering Reference
In-Depth Information
Fig. 1
Mode of action
of
Bt
toxin against
lepidopteran insects
several subspecies of
Bacillus thuringiensis
Berliner. These include
B. thuringiensis
ssp.
kurstaki
and
aizawai
, with the highest activity
against lepidopteran larval species;
B. thuringi-
ensis israelensis
, with activity against mosquito
larvae, black fl y (simuliid), and fungus gnats;
B.
thuringiensis tenebrionis
, with activity against
coleopteran adults and larvae, most notably the
Colorado potato beetle (
Leptinotarsa decemlin-
eata
); and
B. thuringiensis japonensis
strain
Buibui, with activity against soil-inhabiting
beetles (Carlton
1993
; Copping and Menn
2000
).
Bt
produces crystalline proteins and kills few
target insect pest species like lepidopteran species.
The binding of the
Bt
crystalline proteins to insect
gut receptor determines the target insect pest
(Kumar
2012
).
Toxicity of
Bti
and some other toxic strains is
commonly imputed to the parasporal inclusion
bodies (
-endotoxins) which are produced during
sporulation time. These endotoxins must be
assimilated by the larvae to accomplish toxicity.
Bt
and their subspecies produce different insecti-
cidal crystal proteins (
δ
-endotoxins), and their
toxicity was determined (Chilcott et al.
1983
;
Aronson and Shai
2001
). These toxins, when
ingested by the larvae, can damage the gut tis-
sues, leading to gut paralysis. After that, the
infected larvae stop feeding and fi nally they die
from the combined effects of starvation and mid-
gut epithelium impairment (Fig.
1
) (Betz et al.
2000
; Zhu et al.
2000
; Darboux et al.
2001
).
Some other microbial pesticides act by out-
competing insect pest organisms. Microbial
δ
Search WWH ::
Custom Search