Isolation, Characterisation And Bioefficacy Analysis Of Bacillus Thuringiensis (Bt) Strains Against Dengue Vectors
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Date
2021-03
Authors
Ho, Lai Yee
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
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. Nevertheless, results
suggested minimal correlations between the examined characteristics of the B.thuringiensis isolates. Bioefficacy analysis showed varying degrees of toxicity, with
three B. thuringiensis isolates (A10C, R2 and A2B) exhibited good larvicidal
properties. Generated LC50 and LC95 values of all three isolates against Ae. albopictus
and Ae. aegypti up to 48 hours’ post-treatment were below 0.3 mg/mL and 0.5 mg/mL,
respectively. Sublethal evaluations of the three best isolates saw inversely impacted
life parameters on treated Aedes spp. larvae, such as decreases in adult emergence,
gender ratio, fecundity, fertility, and adult wing sizes; with R2 giving the highest
adverse sublethal effects. Findings in this study support the idea that distribution of B.
thuringiensis with combinations of insecticidal cry/cyt genes is associated with
presence of targeted insects and may serve as potential broad-spectrum biopesticides
to be incorporated as part of local vector control management programmes.
Description
Keywords
Dengue