Survivors?

After an atomic holocaust, insects may be the only creatures left alive for miles around. Some species can survive a radiation dose 200-300 times greater than that which would kill an elephant or a man. One explanation: cells are most susceptible to radiation damage when they are in the process of dividing. Since many insects, unlike humans, undergo no cell division during much of their lives, they are more highly resistant to radiation.

To test this theory, Canadian Biologist William F. Baldwin chose one of the world's least attractive creatures: a sharp-beaked "kissing bug" (Rhodinus prolixits], a tiny ( 1/2 in. long) brown resident of South America that lives on blood and sometimes sucks at human lips. Dr. Baldwin, a radiation specialist at Atomic Energy of Canada's remote biology laboratory in Chalk River, Ont., went to work on the bug because it signals visually when its cells are dividing: they divide only when Rhodinus needs to grow a new coat. This process occurs after the bug is newly gorged with blood, and then all the cells under its body wall divide simultaneously. Furthermore, it can live for a year on one meal, after drinking up to twelve times its weight. Until its next feeding, its cells are in a nondividing state.

After importing six of the creatures 18 months ago, Dr. Baldwin has bred thousands of them, which he alternately bombards with X rays and gorges with blood. About 400 roentgens has generally been considered a lethal dose for man (see MEDICINE). But a mature kissing bug, Dr. Baldwin finds, can survive 50,000 roentgens. When he bombarded small spots on young kissing bugs with 2,000,000-volt X rays, he found the cells apparently unaffected. But when the insect ate, setting off the mechanism of cell division and molting, the latent damage appeared. The irradiated spots developed blisters and degenerated.

The mechanism of radiation damage is still little understood. In experiments, Dr. Baldwin irradiated a bug sealed inside a chamber containing nitrogen. The oxygen deficiency slowed the bug's cell division, and when it molted, the bug showed two to three times less radiation damage than bugs that were irradiated in normal air. Dr. Baldwin concluded that oxygen deficiency improved radiation resistance. Since cells in humans are continually dividing, man may never hope to achieve an insect's resistance. But Dr. Baldwin is hopeful that the study of his kissing bugs will lead to basic knowledge of how radiation damages cells and what can be done to reduce such damage to a minimum.

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