Standardising bioassays for passive spatial emanators against mosquito vectors

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Abstract
The increasing use of passive spatial emanators (SEs) for vector control has underscored the need for standardised laboratory methods for bioefficacy testing. Peet–Grady (PG) chamber assays are widely used to test volatile insecticides; however, key methodological parameters remain poorly characterised. Here, we investigated how airflow settings (fan speed and baffle setup), mosquito-holding cage design, and cage mesh structure influence mosquito responses to a transfluthrin (TF) passive emanator. Susceptible and pyrethroid-resistant Anopheles gambiae mosquitoes were exposed to TF, and effects were assessed using flight inhibition (FI) and 24-hour mortality as endpoints. The assay was highly reproducible, with 83% agreement in FI dynamics across replicate comparisons. Airflow settings were more strongly associated with FI than cage geometry or mesh structure, with 5.86- to 9.57-fold higher odds of FI without a baffle. In contrast, 24-hour mortality varied less across airflow settings, suggesting that FI may be a more sensitive assay endpoint. Time to FI thresholds was up to 4-fold shorter under the medium fan speed setting without a baffle than under the low fan speed setting with a baffle. Cage mesh structure influenced FI responses, with larger mesh apertures showing 10- to 20-fold higher odds of FI in certain configurations, whereas cage geometry had little effect, supporting the use of a higher-throughput dual-cage configuration. These findings highlight the importance of airflow setting, mosquito-holding cage design, and cage mesh structure in determining FI responses in PG-chamber assays and support their consideration when standardising passive spatial emanator bioassays.
Funding Information
  • Wellcome Trust (209305/Z/17/Z)
  • IVCC through Gates Foundation (INV-058567)