A Cytogenetic Study of the Effects of X-Irradiation onAedes Aegypti

SUMMARYCytogenetic effects of X-rays (500, 1000, 2000, 4000 r) on the NIH strain of Aedes aegypti L. have been studied. Larvae were reared under controlled conditions and were irradiated six days after hatching at a time when most were in the early fourth instar. Five to ten larvae were fixed for cytological examination at intervals of 0, 1½, 6, 12, 18, 36 and 72 hours after irradiation. Mitotic chromosomes were studied from squash preparations of larval brains stained with acetolactic orcein. Mitotic activity was measured in terms of the total number of dividing cells per brain.Initially X-irradiation inhibited cell division. Mitotic activity was almost completely suppressed 1½ hours after irradiation. After a time (depending on dose used), this effect was replaced by a great increase in mitotic activity. Twelve hours after irradiation, the larvae exposed to 500 and 1000 r showed about twice as many mitotic figures as did the unirradiated material. The increase in mitotic activity at higher doses was less extreme and took longer to occur. Among the chromosomal aberrations noted were deletions, inversions, exchanges, rings, dicentrics and anaphase bridges. Explanations for the induction of these aberrations habe been discussed.A relationship existed between the dose received and the developmental stage at which an individual died. The higher the dose, the earlier the death occurred. Furthermore 2000 r or more resulted in almost 100% mortality. Some possible causes of X-ray-induced mortality and changes in fertility have been suggested.