Pengasingan, saringan dan pengecaman agen mikrobial tempatan untuk mengawal nyamuk yang penting dari segi kesihatan awam di Malaysia
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Date
1995
Authors
Han Lim, Lee
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Abstract
Mosquito-borne diseases are today still important
tropical diseases causing significant morbidity and mortality.
Prompted by problems of chemical control of mosquitoes,
renewed interest in biological control especially
the microbial control agents has been revived. The major
objective of the present undertaking is to isolate and
identify '9Tomising Malaysian isolates of bqcterial control
agents of mosquito and to examine their role in vector
control. Field collection of soil and water samples from
ecologically diversified potential mosquito breeding habi-
·tats in Malaysia for the purpose of isolating potential
microbial control agents was conducted. To date, a total of
876 soil & water samples and dead insects were collected
and from these samples, 3 922 bacterial colonies were obtained
after culturing on different types of media. These
microbial agents were completely screened for their larvicidal
activity against Aedes aegypti and Culex
quinquefasciatus. From such screenings, a total of 29
Bacillus thuringiensis isolates were obtained which included
25 isolates of serotype H-14, 1 isolate each of serotype
H-7, H-8a8b, an isolate related to H-28 and an untypable
isolate tentatively named as subsp malaysianensis (for
identification purpose). In addi~ion, 8 isolates of B.
sphaericus were also obtained. These included 4 isolates
each of serotype H-5a5b and H-25. Of special interest is an
isolate of B. sphaericus H5a5b which also exhibits antimicrobial
characteristics in addition to its mosquitocidal
activity. Other larvicidal microbial agents isolated were· a
new anaerobic Clostridium bifermentans serovar malaysia and
2 isolates of Pseudomonas pseudornallei. All these bacterial
agents exhibited high activity against mosquito larvae.
Field evaluation of an isolate of B. thuringiensis H-14
(IMR-BT-8) and B. sphaericus (IMR-BS-4) was conducted
against ·'-A.{J. karwari. At 1.8 kg/ha, IMR-BT-8 was effective
for 5 days, whilst IMR-BS-4 was effective for 11 days at
0.8 kg/ha. In trial against Cx. pseudovishnui, IMR-BT-8
drastically reduced the larval population 24 and 48 h postspraying.
However, the effect of IMR-BT-8 on Mansonia at
2.5 kg/ha in a limited field trial was inconclusive. At 2.0
mg/1, IMR-BT-20 was effective for more than 3 weeks against
Ae. albopictus breeding in earthen jars and about 20 days
in tyres at 1.0 mg/1. IMR-BT-8 was less effective in similar
habitat. In summary, this screening programme has been
highly successful. Similar techniques could therefore be
expected to be applicable in other tropical regions.
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Keywords
Agen mikrobial , Mengawal nyamuk , Kesihatan awam