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Abstract

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 the development of knowledge on public health. A Bti was developed in this study and tested following the technical specifications of ISO 17025:2017. C. quinquefasciatus Say 1823, a major vector of filariasis in the neighbouring 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 C. 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 C. quinquefasciatus colonies showed 1.86-, 22.31-and 4.25-fold increases in resistance, respectively, in the 25 th 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 31 st , 68 th and 41 st generations, respectively. These studies indicated that the laboratory based-Bti is effective and should be developed as a larvicidal product. C. quinquefasciatus developed resistance to Bti slowly, and the induced resistance declined rapidly compared to the resistance to Bsph and temephos.

<i>In vitro</i> and <i>in situ</i> Activity of <i>Cymbopogon citratus</i> Essential Oil Against <i>Alternaria alternata</i> and <i>Phomopsis carica-papayae</i>, Causal Agents of Papaya Leaf Diseases

“…This test was carried out following a curative treatment according to the modified protocol of Davy et al [6]. Papaya leaves apparently showing no symptoms of necrosis or staining were harvested, washed and disinfected.…”

“…However, the use of the latter has been restricted due to their high toxicity, persistence in the environment, non-biodegradability and high carcinogenic potential. They are a threat to human health, which is why there is growing interest in a healthier, environmentally-friendly control alternative [6].…”