The World Health Organization (WHO) provides standardized procedures and diagnostic doses for evaluating the susceptibility of mosquito larvae to temephos, an organophosphate larvicide. These guidelines are designed to monitor resistance, particularly in Aedes aegypti, the primary vector for dengue and Zika.
WHO Standardized Temephos Procedure
- Diagnostic Concentration: To test for susceptibility/resistance, larvae are exposed to a diagnostic dose of 0.012 mg/L to 0.02 mg/L of temephos.
- Methodology: The standard WHO bioassay involves testing third or early fourth-instar larvae, usually with 24-hour exposure, to measure mortality.
- Standard Solutions: Standardized solutions (often 50 ml bottles) for resistance testing are provided, with concentrations typically ranging from 0.05 mg/l to 156.25 mg/l, depending on the specific insect and resistance level.
- Control Requirement: A control group using distilled or deionized water (without insecticide) is mandatory for every test to ensure validity.
- Application in Water: For mosquito larviciding, the recommended application rate for temephos in potable water is 1 ppm (1 mg/L).
Quality Control and Specifications
- Product Standards: Temephos used in public health must comply with WHO specifications (e.g., 340/TC, 2008), ensuring the technical material is high quality (min 880 g/kg).
- Formulation: It is used as emulsifiable concentrates (EC) or sand granules (GR), which are generally applied to containers, ponds, and water sources.
- Monitoring Resistance: Due to potential resistance, the WHO emphasizes regular monitoring of larval susceptibility.
Safety Profile
- Hazard Rating: WHO classifies temephos as Class U (“unlikely to present acute hazard in normal use”).
- Safety in Drinking Water: Temephos is considered safe for treating drinking water at the recommended dose of 1 mg/L, as the ADI (Acceptable Daily Intake) is rarely exceeded.
