ISOLATION AND SCREENING OF BACILLUS S P E C I E S AGAINST CULEX LARVAE IN ZARIA AREA
ISOLATION AND SCREENING OF BACILLUS S P E C I E S AGAINST CULEX LARVAE IN ZARIA AREA
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Date
2000-11
Authors
UMARU, NUHU FILIBUS
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Abstract
Studies on isolation and identification of Bacillus species against
mosquito larvae were carried out in Zaria between the months of
February 1995 and May 1997 with a view of establishing potent strains
with bio-control potentials against mosquito larvae.
Samples of mud and dead mosquito larvae were collected on
filter paper separately and dried in an oven at 30oC for seven (7) days
and later heated at 80oC for 20 minutes to destroy non-spore forming
bacteria. The samples were screened for spore-forming bacilli by
streaking on nutrient agar plates enriched with 0.3% yeast extract;
isolates were identified and then tested for their ability to kill Culex
mosquito larvae in water.
A total of 78 soil mud samples and 150 dead mosquito larvae
were collected: out of the soil samples, 31 ( 39.28%) produced colony
growth on nutrient agar but none showed cidal activity against
mosquito larvae. Of the 150 mosquito larvae samples, 27 (18%)
produced colony growth on nutrient agar; 23 (85.2%) of this showed
activity against Culex mosquito larvae. The identities of the mosquito
killing bacteria was revealed as Bacillus cereus(2 lor 91.3%), Bacillus
thuringiensis pakistani 11-13, (lor 4.3%, and Bacillus thuringiensis
tohokuensis H-17, (lor 4.3%).
Thus, Bacillus cereus emerged as the dominant species isolated
from dead mosquito larvae with potent activity against Culex larvae.
The lethal concentration that could kill 50% of the Culex larvae
(LC50) were determined to be 0.025 mg/L for Bacillus cereus, 0.012
mg/L for Bacillus thuringiensis Pakistani H-13, and 0.013mg/L
Bacillus thuringiensis tohokuensis H-17. A reference standard strain
of B. sphaericus (no SPH 88 - 2362) exhibited an LC50 at 0.005mg/L.
There was significant difference (P<0.05) in activity between
Bacillus cereus, Bacillus thuringiensis and the standard - Bacillus
sphaericus and the null hypothesis was rejected. On the other hand,
no significant difference(p>0.05) in activity was observed between both
varieties of Bacillus thuringiensis isolates and Bacillus sphaericus
(standard), thus the null hypothesis is accepted and Bacillus
thuringiensis pakistani and B. thuringiensis tohokuensis H-17 are
accepted as potential agents found in the Zaria area.
The study therefore concludes that isolates of B. thuringiensis
with bio-control potential against Culex larvae exist in the Zaria
environment
Description
THIS THESIS IS SUBMITTED TO THE POSTGRADUATE SCHOOL
OF AHMADU BELLO UNIVERSITY IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE AWARD OF MASTER OF SCIENCE
(M.Sc.) DEGREE IN ZOOLOGY IN THE DEPARTMENT OF
BIOLOGICAL SCIENCES, AHMADU BELLO UNIVERSITY, ZARIA
NOVEMBER 2000.
Keywords
ISOLATION,, SCREENING,, BACILLUS,, S P E C I E S, CULEX,, LARVAE,, ZARIA,