Ho, Lai Yee
(2021)
Isolation, Characterisation And
Bioefficacy Analysis Of
Bacillus Thuringiensis (Bt) Strains
Against Dengue Vectors.
PhD thesis, Perpustakaan Hamzah Sendut.
Abstract
A mounting public health concern over mosquito-borne diseases, a global
economic burden, and failure of current control measures due to escalating
development of insecticides resistance have intensified the search for alternative ecofriendlier
vector control strategies. An investigation was conducted to explore the
toxicity profiles of indigenous B. thuringiensis isolates from an ex-tin mining area.
Verification was performed through microscopic identification and biochemical
characterisations. Morphological features of the crystal proteins were assessed using
scanning and transmission electron microscopy. Distribution of insecticidal genes and
crystal protein classes were examined through PCR and SDS-PAGE analyses.
Eventually, these isolates were screened for larvicidal and sublethal efficacies against
laboratory strains of Ae. albopictus and Ae. aegypti. From the seven sampling sites, 13
B. thuringiensis isolates were obtained (A10C, D10D, N6Bss, 6a3s, 8a3, 8a3s, 8b3,
R1, R2, R3, D1C, A2B and C6D) with an overall B. thuringiensis index of 0.07.
Spherical-shaped crystal proteins were present in all isolates, while lesser numbers of
ovoidal- and cuboidal-shaped crystal proteins were noted. Protein profiles revealed
presence of eight classes of crystal proteins (Cry2, Cry4C/4D, Cry6A, Cry10, Cry11,
Cry34, Cry35, Cyt1/2). Four of the isolates (N6Bss, 8a3, R1 and A2B) harboured all
six of the examined insecticidal genes (cry1, cry2, cry4, cry10, cry11 and cyt2), which
are known to produce Dipteran-specific delta-endotoxins.
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