Booth, Ashley Lane (2016-04). Radioresistance of Mosquitos Exposed to Continuous Sub-Lethal Doses of Ionizing Radiation. Master's Thesis.
This experiment is an investigation of the mosquito's ability to adapt to high levels of background gamma radiation. Radiation was used as a selective pressure to induce radioresistance among a group of Aedes aegypti mosquitos. Mosquitos were grouped into a High Background Group (HBG) or a Low Background Group (LBG), the LBG being the control group. The HBG was exposed to a continuous field of ionizing gamma radiation significantly higher than the normal background radiation level for the Bryan/ College station (B/CS) area. The HBG spent more than 23 hours per day exposed to the increased levels of radiation. The dose rate ranged from 36 rad/day to 28 rad/day over the course of several weeks. The radiation exposure to the mosquitos began at the larval stages and continued throughout the adult stages of the mosquito's lifecycle. During the developmental stages of life living tissues are most susceptible to radiation. Thus by delivering radiation doses during those stages, it provided greater opportunity to induce radioresistance in the mosquitos DNA. Mosquitos in the LBG were reared using the same techniques as the HBG, but in radiation levels similar to that of typical background radiation levels in the B/CS area. The average normal background dose rate at the mosquito lab location is 24 mrem/ year. After mosquitos in the HBG obtained a total dose of approximately 1000 rads over the course of several weeks, the HBG was exposed to a challenge dose provided by a high dose rate gamma source which delivered a total dose of about 70,000 rads over the course of 7-10 hours. Additionally, mosquitos in the LBG were also exposed to the same challenge dose for an equivalent amount of total dose, +-10%. Upon completion of the challenge dose, the LBG was cared for utilizing the same methods as before. The HBG, however, did not receive additional high doses of radiation and were only exposed to background radiation similar to the exposure to the LBG. Survival percentages were documented and compared immediately following the challenge dose and continued until all mosquitoes perished. The mosquitos in the HBG consistently had higher survival rates when compared to the LBG. For mosquitos in the first round LBG, 50% lethality was reached on Day 3 post challenge dose. Mosquitos in the second round LBG, 50% lethality on Day 1 post challenge dose. After the challenge exposures to the LBG, 62% of round one and 72% of round two survived the duration of the exposure. Mosquitos in the first round HBG reached 50% lethality on Day 6 post challenge dose. The second round HBG reached 50% lethality on Day 9 post challenge dose. After the challenge exposure to the HBG, 92% of round one and 100% of round two survived the duration of the exposure. One specific mosquito from the first HBG developed an abnormal abdominal cavity prior to the challenge dose, but it is not believed to have contributed to the mosquito's radioresistance.