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

Abstract

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.

A rapid quality control test to foster the development of the sterile insect technique against Anopheles arabiensis

“…Following on from previously reported research from IPCL [10], a range of chilling temperatures that were known to be tolerable (4, 8 and 10 °C), were selected, A lower temperature of 0 °C was chosen with the intention to reduce quality post-chilling as it was beyond the range of temperatures previously tested and found to be tolerable. On day 3, cages of 250 adult males were immobilized at each of the above temperatures for a period of 2 h, with control males left under insectary conditions (27 ± 1 °C).…”

“…It seems logical to assume that a release campaign involving mosquitoes will involve a similar process as to what is currently used in other insects including Mediterranean fruit flies [14] and tsetse flies [13] and thus understanding how chilling temperature impacts male quality is fundamental to a successful campaign. A previously reported study conducted within the IPCL laboratory [10], exposed male An. arabiensis to a range of chilling temperatures for various durations and concluded that only exposure to 2 °C, the coldest temperature tested, for 24 h, the longest duration tested, significantly reduced survival in comparison to non-chilled control males.…”

“…Optimal transportation conditions have been advised for An. arabiensis [10] in addition to a study investigating various release conditions for both An. arabiensis and Ae.…”

The Sterile Insect Technique (SIT) – an introduction

“…Ma€ ıga et al (2017) investigated laboratory rearing methods to optimize adult longevity and egg production in Anopheles arabiensis Patton (Diptera: Culicidae) for an SIT program still in its infancy. Culbert et al (2017) also present data on A. arabiensis, and show that if males are kept at temperatures between 4 and 10°C, and are given adequate ventilation in transportation containers, survival over a 24-h period is not significantly reduced. Flores et al (2017) took a 'traditional' approach in their field study of Anastrepha obliqua (McQuart) (Diptera: Tephritidae).…”

“…Culbert et al. () also present data on A. arabiensis , and show that if males are kept at temperatures between 4 and 10 °C, and are given adequate ventilation in transportation containers, survival over a 24‐h period is not significantly reduced.…”