International Journal of Applied Microbiology and Biotechnology Research
ISSN: 2053-1818
Vol. 8(5), pp. 58-65, October, 2020
doi.org/10.33500/ijambr.2020.08.007

Development of larvicidal Bacillus thuringiensis var. israelensis by the Thai NIH and its comparison to Bacillus sphaericus and temephos in a selection experiment with the mosquito

Uruyakorn Chansang*, Nittaya Methawanitpong, Danaporn Saraprug, Porntida Phetsuwan, Nuntaporn Ponsuwan and Pornchai Wiriyasaranont

National Institute of Health, Department of Medical Sciences, Ministry of Public Health, Nonthaburi 11000, Thailand.

*To whom correspondence should be addressed. E-mail: uruyakorn.c@dmsc.moph.go.th.

Received 15 August, 2020; Received in revised form 25 September, 2020; Accepted 30 September, 2020.

Keywords:
Bacillus thuringiensis subsp. israelensis (Bti), Bacillus sphaericus (Bsph), temephos, Culex. quinquefasciatus, resistance induction.

Insecticide resistance poses a serious obstacle to the control of insect vectors. The microorganisms Bacillus thuringiensis subsp. israelensis (Bti) and Bacillus sphaericus (Bsph) have been used as alternative larvicides to a variety of mosquitoes such as Culex quinquefasciatus which was reported to be resistant to some groups of insecticides. National Institute of Health (NIH), Thailand has authority and function in development of knowledge on public health. A Bti was developed in this study and tested following the technical specifications of ISO 17025:2017. Culex quinquefasciatus Say 1823, a major vector of filariasis in neighbor countries has been monitored at the borders of Thailand. The effectiveness and appropriate long-term use of Bti, together with the potential for recovery from insecticide resistance, were tested against the standard susceptible strain of Cx. quinquefasciatus by a selection pressure method. Also, the commercial Bsph and temephos were tested in parallel to determine the suitable time of use. The powdered Bti was produced with a potency of 20,839.98 ITU/mg. The bioassay performed with Bti, Bsph and temephos to standard Cx. quinquefasciatus colonies showed 1.86-, 22.31- and 4.25-fold increases in resistance, respectively, in the 25th generation. The tests were continued without further larvicide exposure to determine the interval over which the resistance decreased. The resistance of the mosquitoes to Bti, Bsph and temephos declined to 0.99, 10.64 and 1.03 in the 31st, 68th and 41st generations, respectively. These studies indicated that the laboratory based-Bti is effective and should be developed as a larvicidal product. Cx. quinquefasciatus developed resistance to Bti slowly, and the induced resistance declined rapidly compared to the resistance to Bsph and temephos.

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