Abstract
BackgroundTo ensure the success of a mosquito control programme that integrates the sterile insect technique (SIT), it is highly desirable to release sterile males with a maximal lifespan to increase release effectiveness. Understanding sterile male survival under field conditions is thus critical for determining the number of males to be released. Our study aimed to investigate the effect of mass rearing, irradiation, chilling, packing and release time on irradiated male mosquito longevity.MethodsAnopheles arabiensis and Aedes aegypti immature stages were mass-reared using a rack and tray system. Batches of 50 males irradiated at the pupal stage were immobilised, packed into canisters and chilled for 6 hours at 6 °C. Mosquitoes were then transferred either in the early morning or early evening into climate chambers set to simulate the weather conditions, typical of the beginning of the rainy season in Khartoum, Sudan and Juazeiro, Brazil for An. arabiensis and Ae. aegypti, respectively. The longevity of experimental males was assessed and compared to mass-reared control males subjected either to simulated field or laboratory conditions.ResultsThe combined irradiation, chilling and packing treatments significantly reduced the longevity of both An. arabiensis and Ae. aegypti under simulated field conditions (P < 0.001). However, packing alone did not significantly reduce longevity of Ae. aegypti (P = 0.38) but did in An. arabiensis (P < 0.001). Overall, the longevity of mass reared, irradiated and packed males was significantly reduced, with the median survival time (days) lower following an early morning introduction (4.62 ± 0.20) compared to an evening (7.34 ± 0.35) in An. arabiensis (P < 0.001). However, there was no significant difference in longevity between morning (9.07 ± 0.54) and evening (7.76 ± 0.50) in Ae. aegypti (P = 0.14).ConclusionsOur study showed that sterile mass-reared males have a reduced lifespan in comparison to laboratory-maintained controls under simulated field conditions, and that An. arabiensis appeared to be more sensitive to the handling process and release time than Ae. aegypti. Longevity and release time are important parameters to be considered for a successful area-wide integrated vector control programme with a SIT component.
Highlights
To ensure the success of a mosquito control programme that integrates the sterile insect technique (SIT), it is highly desirable to release sterile males with a maximal lifespan to increase release effectiveness
They were maintained at the Insect Pest Control Laboratory (IPCL) of the joint Food and Agricultural Organisation/International Atomic Energy Agency (FAO/IAEA) Division of Nuclear Techniques and Agriculture, Seibersdorf, Austria, under controlled temperature, relative humidity (RH) and light regimes (27 ± 1 °C, 70 ± 10% RH, 12:12 h light:dark (L:D) photoperiod with 1 h periods of simulated dawn and dusk)
Effect of packing on male longevity of Anopheles arabiensis and Aedes aegypti The longevity of 50 sterile males packed in a small tube and chilled at 6 °C for 6 h was compared to 50 sterile males chilled at 6 °C for 6 h in a small Bugdorm cage
Summary
To ensure the success of a mosquito control programme that integrates the sterile insect technique (SIT), it is highly desirable to release sterile males with a maximal lifespan to increase release effectiveness. Understanding sterile male survival under field conditions is critical for determining the number of males to be released. Our study aimed to investigate the effect of mass rearing, irradiation, chilling, packing and release time on irradiated male mosquito longevity. There are many potential stressors a sterile male mosquito must endure before it is released into the field, including mass-rearing, sex-separation, irradiation, marking, handling, immobilisation and packing. It is critical to determine the relative impact that each step has on insect quality to develop a standardised set of guidelines for each stage that imposes the least cost. Optimal transportation conditions for sterile male An. arabiensis adults have been studied [6]
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