Optimised conditions for handling and transport of male Anopheles arabiensis: effects of low temperature, compaction, and ventilation on male quality

Developing optimal conditions for handling and transport of sterile male mosquitoes, prior to their release, is critical for the sterile insect technique (SIT) to be successful. No data currently exist for Anopheles arabiensis Patton (Diptera: Culicidae) concerning the effects of chilling at different temperatures and for different time lengths on subsequent survival. Additionally, it must be determined whether immobile mosquitoes are capable of producing metabolic heat, the maximum packing density in one release cassette during transport, and their toleration level to compaction. Male An. arabiensis were exposed to 2, 4, 6, and 10 °C for 1, 4, 8, or 24 h. Survival was then monitored for 14 days and compared with untreated controls maintained at 25 °C. Short-term (24 h) survival was assessed following immobilisation at 6 °C for 6 h under compacted and non-compacted conditions and compared with non-immobilised controls. The experiment was repeated to assess long-term (1–14 days) survival with varying levels of ventilation. Metabolic heat was assessed in immobilised males (compacted and non-compacted) and compared with males maintained at 28 °C for 2 h. The weight and volume of males were determined to guide the design of the release cassette. Male An. arabiensis were maintained at a temperature range of 4–10 °C for 24 h without any significant negative effect on their survival. Compaction did not significantly affect survival; however, it fared better with increased ventilation. Immobile males did not produce any metabolic heat, even when compacted. This study identified initial parameters considered critical for the transport of sterile male An. arabiensis prior to release without any detrimental effect on their survival. Further investigation is required to assess the effects of combining these chosen treatments with irradiation. Additionally, the effect of immobilisation, compaction, and irradiation on the most critical parameter for SIT (male competitiveness) is the subject of future studies.