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DTIE-P
CONF-744-1
OCT $1964
RECENT DEVELOPMENTS IN RESEARCH ON RADIATION AND CHEMICAL
MUTAGEN EFFECTS IN INSECTS*
3. C. von Dorstel
Biology Division, Oak Ridge National Laboratory,
Oak Ridge, Tennessee
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---LEGAL NOTICE
This report na prepared as an acenant of Governor ont sponsored work. Hether the United
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with the Commuteria, o no employment with me contractor.

*Research sponsored by the U. S. Atomic Energy Commission under contract
with the Union Carbide Corporation.
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Running head: Radiation and Chemical
tagen Effects
Send proofto: Dr. R. Er von Borstel
Biology Division
Oak Ridge National Laboratory
P. O. Box Y
.. Ridge, Tennessee 37831
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The induced sterility discussed at this conference can be divided
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into two major components, dominant lethality and true sterility from gonial
cell killing. There are of course other types of sterility such as sperm
inactivation. Also there is an effect of the radiation whereby the males
are weakened, which is a kind of pseudosterility. This weakening of the
difficulty since males released in the field must be vigorous to successfully
compete. I shall discuss some of the possible ways to lessen the male-
weakening effect. after presenting a short surmary of recent advances made
in the theory of dominant lethality.
I would like to present a model, though not a unique one, which provides
a reasonable explanation for most of the parameters associated with dominant
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lethality induced in sperm. The theory is important for the irradiation-of-male
method of insect control because it has inherent in its consequences an
istivities.
explanation of the resistance to radiation of the sperm of Lepidoptera.
There is considerable circumstantial evidence that induced dominant
lethality is associated with chromosome breakage. One of the best pieces of
evidence for this is that a diploid sperm is exactly twice as sensitive to
radiation as a haploid sperm (Mortimer and von Borstel, 1963), and this effect
1s equivalent to the cüpacity of radiation to induce chromosome breaks in
a ploidy serie: (Conger and Johnston, 1956). These are the only two radiation
effects in ploidy series which are the same, since higher ploidies usually
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confer a kind of protection against radiation in growing plants or in insect
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Let is assume that dominant lethality in the wasp Habrobracon or
in the fly Drosophila is induced, by formation of chromosome bridges; this
is an assumption based on a considerable body of data (cf. von Borstel,
1960). The initial exponential component of a dose-hatchability curve
following irradiation of sperm could come from terminal deletions of the
chromosome arms which form chromosome bridges when a new chromosome is
synthesized, and this would follow the expression
(1)
S = e-KD
where S is the surviving fraction, D is the dose of radiation, and k is
the sensitivity of the chromosome. The multihit component of the
dose-hatchability curve (and Lepidoptera have only the multihit type of
sperm curve) could possibly come from formation of dicentric translocations
at a limited number of binomially distributed sites in a sperm where the
chromosomes lie close enough together for a translocation to be formed when
both are broken. This would follow the expression
S = (1 - (1 - e-KD, 2,
(2)
where m is the number of sites; the 2 in the exponent refers to the two
chromosomes that must be broken within the site.
Together, equations (3.) and (2) are
S = e-*2D(1 - (1 - e-k2D, 2, m
(3)
which can give an explicit, though, as mentioned before, not necessarily
a unique, description of the dose-hatchability curve following irradiation
of the sperm of Hebrobracon or Drosophila
The model deriving from equation (2) has been developed earlier
(von Borstel; 1960; Bender and Wolit, 1961; Wolff, 1961) to describe
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dose-action data on the induction of dicentric translocations, and it was
used to analyze data on detachments, through translocations, of attached-X
chromosomes (Wolff, 1962; Parker, 1963). Since the frequency of total
induced reciprocal translocations can be measured independently, and since
these should be equal in number to the lethal dicentric translocations
formed and measurable by equation (3), it is expected that a test of
consistency of the above model will be made soon.
There are at least three possible ways in which the radiation effect
on the weakening of male insects might be lowered: (1) lowering the dose
to that just above where 100% killing of the gonial cells can be
accomplished, (2) fractionating the doses, and (3) irradiating the males
with radiation of higher LET.
It is not necessary for the irradiation-of-male method to succeed
that 99.9%, 99%, nor 90% of the sperm contain induced dominant lethals. It
would work even at lower lethal limits providing that the females (which
usually have to be released as well) have no viable eggs and that neither
males nor females will have repopulation of the gonial cells. This may be
possible in certain insects and should certainly be investigated when other
methods fail. Also, although hatchability is a convenient and accurate
criterion of damage, reduced adult survival is all that really matters; with
flies and wasps the dose can probably be reduced about 20% over that used
to obtain 99% dominant lethality, providing again that the gonial cell
populations are eliminated. This reduction of doses for the same final
effect on viability for adults and eggs may vary from insect to insect and
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should also be investigated.
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Dose-fractionation allows time for certain types of radiation damage
on
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to recover between the doses. Interestingly enough, the dose-fractionation
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allows recovery of most types of damage excet the genetic and dominant
lethal damage induced in sperm (cf. Sobels, 1963). It might be possible
to increase the vigor of males without reducing their lethal capacity by
using fractionated or chronic radiation.
Dominant lethality is approximately doubled by 1 MeV neutron over
that oü equivalent doses (kilorep) of gamma or X radiation, whereas
recessive lethality only increases by about 50% (Edington and Randolph,'
1958). This should be investigated for the effect on weakening of males.
It is possible that a nuclear reactor or some type of heavy ion generator
may be the radiation source of choice for certain insects.
Also, weakening of the males is lessened if the insects can be
irradiated as adults rather than as pupae, or as late pupae rather than
as early pupae.
The great potential for the use of chemosterilants for insect control
has barely begun to be explored since it was first suggested by Knipling
(1959). The chemicals are in many ways simpler to use than the radiation
and the possibility exists that it can be used in the field. Of course the
hazards are great too; long-lived chemosterilants could possibly be as
hazardous as heavy fallout from nuclear detonations, and trace amounts
might be carried by the very insects that are being treated in the field.
Nevertheless, different chemosterilants have different actions. Certain
of them undoubtedly induce differing ratios of dominant lethal to recessive
lethal mutations. For example, the alkylating agent ethyl methanesulfonate
appears to induce a low ratio of dominant lethal to recessive lethal
mitations, and the ratio is increased when nitrogen mustard is used (Löbbecke
and von Eorstel, 1962). Apholate appears to have a higher dominant lethal to
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recessive lethal ratio than either APO or MAPO in Neurospora (Kaney and
Atwood, 1964).
Such relations should be sought among the better chemosterilants and
then these should be tested for long-term somatic effects in mice such
as ability to induce tumors or to reduce the age of senescence. The
somatic studies program directed by A. C. Upton at the Biology Division,
Oak Ridge National Laboratory, could perhaps be called upon or used as a
model for studying these types of effects. It is possible that an
excellent chemosterilant could be found for use in the field which would
have no debilitating effects on hunians or on vertebrates in general.
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REFERENCES
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Bender, M. A and S. Wolff 1961 X-ray-induced chromosome aberrations and
reproductive death in mammalian cells. Am. Nat. 95: 39-52.
Conger, A. D. and A. H. Johnston 1956 Polyploidy and radiosensitivity.
Nature, London 178: 271.
Edington, C. W. and M. L. Randolph 1958 A comparison of the relative
effectiveness of radiations of different average linear energy transfer
on the induction of dominant and recessiire lethals in Drosophila.
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man
and was carries
winess Intele
nter
Genetics 43: 715-727.
Kaney, A. R. and K. C. Atwood 1964 Radiomimetic action of polyimine
chemosterilants in Neurospora. Nature 201: 1006-1008.
Knipling, E. F. 1959 Sierile-male method of population control. Science
130: 902-904.
Lóbbecke, E.-A. and R. C. von Borstel 1962 Mutational response of
Habrobracon oocytes in metaphase and prophase to ethyl methanesulfonate
and nitrogen mustard. Genetics 47: 853-864.
Mortimer, R. K. and R. C. von Borstel 1963 Radiation-induced dominant
lethality in haploid and diploid sperm of the wasp Mormoniella.
Genetics 48: 1545-1549.
Parker, D. R. 1963 On the nature of sensitivity changes in oocytes of
Drosophila melanogaster. In Repair from Genetic Radiation Damage
and Differential Radiosensitivity in Germ Cells. Pergamon Press,
London. pp. 11-19.
von Borstel, R. C. 1960 Sulla natura della letalita dominate indotta dalle
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radiazioni. Atti Assoc. Genet. Ital. 5: 35-50.
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Wolff, S. 1961 Sone postirradiation phenomena that affect the induction
of chromosome aberrations. J. Cell. Comp. Phys. 58 (Suppl. 1): 151-162.
Wolff, s. 1962 The kinetics for two-break chromsome exchanges. J., Theoret.
Biol. 3: 304–314.
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44.

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