Date: Mon Dec 22 16:33:26 2003
Posted By: John Moulder, Faculty, Radiation Biology, Medical College of Wisconsin
Area of science: Zoology
Steve, you ask:
I have heard that Cockroaches can withstand an extreme amount of [ionizing]
radiation in comparison with humans.
How much radiation can insets receive and survive?
Is this due to their relatively small surface area, their exoskeleton or
some other factor that prevents absorption, or can they absorb a lot of
radiation without it affecting their tissue as greatly?
You are correct that cockroaches are much more resistant to ionizing
radiation than humans. In fact most (perhaps all) insects are more
resistant to ionizing radiation than all mammals.
For most insects a dose of about 500-700 Gy is required to kill them within
a few weeks of exposure; although cockroaches require 900-1000 Gy (Hassett
and Jenkins, Nucleonics, 1952). Killing insects in less than a few days
requires much higher doses. These doses are for mature insects, the
immature stages of some insects (I don't know of data on baby cockroaches)
can be killed by doses as low as 40 Gy (Blaylock et al, Proc Hawaiian Acad
Some insects can be sterilized at even lower doses, and this has
application in insect control. Screw-worms, for example, can be sterilized
with doses of 25-50 Gy (Bushland and Hopkins, J Econ Ent, 1953).
By contrast, doses as low as 3 Gy caused death of humans in Hiroshima and
Nagasaki (Levin et al, Health Phys, 1992) and doses of about 6 Gy caused
death of fire fighters in the Chernobyl accident (Mould, 1988).
It is not exactly certain what the basis is for the resistance of insects
to ionizing radiation.
- It is not animal size, by itself, because the density of
ionizations produced by X-rays is sufficient that something must be much
less than the size of a mammalian (or insect) cell to be missed by random
- It is not lack of penetration because most types of radiation
can penetrate a cockroach much better than they can penetrate a human.
- There was speculation in the 1950's that the resistance of insects was
due to the fact that most adult insects have few dividing cells, and
dividing cells (insect or mammalian) are more radiosensitive than
non-dividing ones. But this does not work, since immature insects, which
do have a lot of dividing cells, are still radiation-resistant.
- There was speculation in the 1950's that insects might have lower
oxygen tensions, and the lack of oxygen is known to protect cells from
radiation. But this does not work, since we now know that the degree of
protection is only about a factor of 3 (comparing oxic cells to completely
- There was speculation in the 1980's that insect cells might have an
enhanced capacity to repair radiation damage. I can find no
evidence that this speculation was ever proven or disproven.
- There was speculation in the 1950's that the number of
chromosomes influenced radiosensitivity, and that insects had fewer
chromosomes. There may be some truth in this speculation, as we now know
that (in general) the less DNA a cell has the more resistant it is to
ionizing radiation. Since DNA is the critical target for cell killing (in
mammalian as well as insect cells), it is logical that the less DNA there
is, the harder it is to hit. While the density of ionizations produced by
X-rays is sufficient that animal size could not explain resistance, the
density of ionizations is low enough that total cellular DNA content could
- The radiation resistance is inherent to the cells, since cells
derived from insects are also radiation resistant when grown in cell
culture. For example, a dose of 60 Gy is required to produce a 80% kill of
insect cells, while doses of 1-2 Gy are sufficient to generate this level
of killing in mammalian cells (Koval, PNAS, 1983).
So it is clear that insects are resistant to ionizing radiation and that
this resistance is an inherent property of their cells. But it is not
clear exactly what the basis of this cellular resistance is, although the
dominant theory is that it relates to the relatively small amount of DNA in
One of the difficulties is assessing possible mechanisms is that very
little work on insect radiobiology has been done since the mid-80's. I
looked at the past 40 years of papers in one of the main radiobiology
journals, Radiation Research. I found 45 papers on insect
radiobiology, but the last was published in 1992, and over half were
published prior to 1975.
Professor of Radiation Biology
Senior Editor, Radiation Research
Medical College of Wisconsin
- TM Koval: Intrinsic resistance to the lethal effects of x-irradiation
in insect and arachnid cells. Proc. Natl. Acad. Sci (USA) 80:4752-4755,
- DS Grosch and LE Hopwood: Biological Effects of Radiation, Academic
- ZM Bacq and P Alexander: Fundamentals of Radiobiology, Pergamon, 1961.
- WD Clauss: Radiation Biology and Medicine, Addison-Wesley, 1958.
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