Effects of Chilling and Anoxia on the Irradiation Dose-Response in Adult Aedes Mosquitoes

Abstract

The success of the sterile insect technique (SIT) relies on the achievement of high levels of sterility and mating success of the factory-reared sterile males and thus their biological quality, which can be enhanced by the reduction of stress factors encountered during rearing, handling, and irradiation procedures. The achievement of consistent sterility levels requires reliable and standard irradiation protocols. Additionally, mosquito adults require immobilization prior to, and during irradiation to increase processing efficiency and to avoid physical damage caused by movement in restricted space. Common methods for immobilization include chilling and anesthetics such as nitrogen. Here we assessed the effects of chilling and exposure to nitrogen on the irradiation dose-response of Aedes mosquitoes, and their downstream effects on some male quality parameters including longevity and flight ability. We found that chilling does not incur damage in the insects in terms of longevity and flight ability when chilling duration and temperature are carefully controlled, and a recovery phase is provided. Irradiation in nitrogen shows high radioprotective effects during irradiation, resulting in reduced induction of sterility. Overall, longevity of males can be improved by irradiating in anoxia, however the exposure to nitrogen itself comes with negative impacts on flight ability. The results reported here will assist in the standardization and optimization of irradiation protocols for the SIT to control mosquito populations of medical relevance.

Response of male adult Aedes mosquitoes to gamma radiation in different nitrogen environments

“…Irradiation in low-oxygen environments (for example, in nitrogen) has been reported to have a radioprotective effect with a beneficial impact on the quality of sterile males in many insect species ( Vreysen, 1995 ; Fisher, 1996 ; Mutika and Parker, 2006 ). However, its effect on mosquitoes was not clear ( Hallinan and Rai, 1973 ; Curtis, 1976 ; El-Gazzar et al, 1983 ; Yamada et al, 2022 ) and needed to be investigated further.…”

“…A recent study also found a reduction in the male flight ability of Ae. albopictus irradiated at 45 Gy in nitrogen compared with irradiation in normoxia as well as unirradiated males ( Yamada et al, 2022 ). However, in our study, the relative differences observed in the male flight ability between the doses inducing nearly full sterility in air and nitrogen treatments were only approximately 10%.…”

“…albopictus males, aged 1–2 days old, were transferred to each vial. After the mosquitoes were transferred, the vials were closed with the screw tops, and the tops were sealed with PTFE Thread Seal Tape (Sigma-Aldrich, USA) before flushing with N 2 , as described by Yamada et al (2022) . To flush N 2 in the vial, two syringe needles were inserted from the top.…”

“…However, the quality of the sterile males can be compromised if the chilling temperatures and duration are not carefully controlled. Indeed, many studies on the effects of chilling on insect quality have reported negative effects (reviewed in Yamada et al, 2022 ). Aiming for a more reliable outcome regarding quality following adult mosquito irradiation, the role of nitrogen has been investigated ( Helinski et al, 2009 ).…”

“…aegypti in nitrogen resulted in better competitiveness compared with irradiation in air, although higher doses were required to achieve full sterility ( Hallinan and Rai, 1973 ). A recent study ( Yamada et al, 2022 ) involving Ae. albopictus also showed a radioprotective effect of nitrogen at 45 Gy.…”