Purpose The rising incidences of insecticide resistance in mosquito vectors highlight the need for continuous monitoring of their susceptibility to chemical insecticides. Therefore, this study assessed the susceptibility status of the Aedes aegypti mosquitoes against the chemical insecticide Temephos. At the same time, there is a growing global interest in increasing the use of bio-larvicides in vector management programs. In this context, it is important to evaluate the effectiveness of bio-larvicides, such as Bacillus thuringiensis israelensis (Bti) toxins, in comparison to conventional chemical insecticides. Methods To evaluate the susceptibility of Aedes aegypti larvae to chemical and biological larvicides, mosquitoes were collected from various breeding sites within the study area. First-generation (F1) larvae from these populations underwent larvicidal bioassays using Temephos and Bti. Temephos was tested at five different concentrations: 0.01, 0.02, 0.03, 0.04, and 0.05 ppm. Bti was assessed at eight different concentrations: 2, 4, 5, 6, 8, 10, 12, and 14 ppm. Lethal concentrations (LC50, LC90, LC99) were determined for both insecticides. Results At the WHO-recommended diagnostic concentration of 0.02 ppm of Temephos, Aedes aegypti larvae exhibited a mortality rate of 50.33%, indicating confirmed resistance. The calculated LC50, LC90, and LC99 values for Temephos after 24 h of exposure were 0.019 ppm, 0.040 ppm, and 0.072 ppm, respectively. For Bti, the LC50, LC90, and LC99 values were 4.80 ppm, 12.89 ppm, and 27.17 ppm after 48 h, and 4.32 ppm, 11.14 ppm, and 20.73 ppm after 72 h, respectively. The lethal time for 50% mortality (LT50) indicated that Bti concentrations above 5 ppm achieved over 50% larval mortality within 48 h. Conclusion The study underscores a significant decline in Aedes aegypti susceptibility to the chemical larvicide Temephos, posing challenges for vector control programs. In contrast, Bti showed substantial efficacy, suggesting its potential as a viable, eco-friendly alternative. Increasing the Bti share in comprehensive vector management strategies could enhance control measures against mosquito-borne diseases.

Laboratory Evaluation of Susceptibility Status of Aedes aegypti Mosquitoes to Temephos and Bacillus thuringiensis israelensis (Bti) Toxins from Odisha, India

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发表日期：

2026年2月11日

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Basudev Nayak,
Bijayalaxmi Sahu,
Tapan Kumar Barik

摘要

Purpose

The rising incidences of insecticide resistance in mosquito vectors highlight the need for continuous monitoring of their susceptibility to chemical insecticides. Therefore, this study assessed the susceptibility status of the Aedes aegypti mosquitoes against the chemical insecticide Temephos. At the same time, there is a growing global interest in increasing the use of bio-larvicides in vector management programs. In this context, it is important to evaluate the effectiveness of bio-larvicides, such as Bacillus thuringiensis israelensis (Bti) toxins, in comparison to conventional chemical insecticides.

Methods

To evaluate the susceptibility of Aedes aegypti larvae to chemical and biological larvicides, mosquitoes were collected from various breeding sites within the study area. First-generation (F₁) larvae from these populations underwent larvicidal bioassays using Temephos and Bti. Temephos was tested at five different concentrations: 0.01, 0.02, 0.03, 0.04, and 0.05 ppm. Bti was assessed at eight different concentrations: 2, 4, 5, 6, 8, 10, 12, and 14 ppm. Lethal concentrations (LC₅₀, LC₉₀, LC₉₉) were determined for both insecticides.

Results

At the WHO-recommended diagnostic concentration of 0.02 ppm of Temephos, Aedes aegypti larvae exhibited a mortality rate of 50.33%, indicating confirmed resistance. The calculated LC₅₀, LC₉₀, and LC₉₉ values for Temephos after 24 h of exposure were 0.019 ppm, 0.040 ppm, and 0.072 ppm, respectively. For Bti, the LC₅₀, LC₉₀, and LC₉₉ values were 4.80 ppm, 12.89 ppm, and 27.17 ppm after 48 h, and 4.32 ppm, 11.14 ppm, and 20.73 ppm after 72 h, respectively. The lethal time for 50% mortality (LT₅₀) indicated that Bti concentrations above 5 ppm achieved over 50% larval mortality within 48 h.

Conclusion

The study underscores a significant decline in Aedes aegypti susceptibility to the chemical larvicide Temephos, posing challenges for vector control programs. In contrast, Bti showed substantial efficacy, suggesting its potential as a viable, eco-friendly alternative. Increasing the Bti share in comprehensive vector management strategies could enhance control measures against mosquito-borne diseases.