application for insects that infest stored prod- 
ucts and some other materials. Since, econom= 
ically, grain is probably the most important 
stored product with which we have serious 
insect problems, the use of electron and 
gamma radiation for disinfesting grain has 
received much attention. 
The findings and fundamental and applied 
problems of using gamma-radiation treatment 
are well set forth in publications by Cornwell 
et al. on research carried out in the United 
Kingdom (34, 35, 36). The effects of beta, 
gamma, and X-rays on stored-grain insect 
pests are all comparable in their lethal and 
sterilizing properties. Insect control is pos= 
sible using any one of the three following dose 
levels: Doses of about 500,000 rads are re-= 
productively sterilizing, produce death within 
24 hours, and provide a high measure of con- 
trol of the microflora, probably allowing grain 
storage at higher moisture contents. Doses of 
about 100,000 rads produce sterilization, death 
in about a week, minimize insect feeding dam-= 
age prior to death, and sterilize mites. Doses 
of 15,000-20,000 rads provide sterilization 
of the insects and death of the adults in 
2-5 weeks and arrest the development of 
immature stages. Development of the eggs 
and larvae of granary weevils (Sitophilus 
granarius (L.)) is prevented by doses as low 
as 5,000 rads, but complete sterilization of 
the adults requires a higher level of treat- 
ment. 
Since radiation accelerates the mutation 
rate, there is a possibility with sublethal 
treatments that insects might develop resist- 
ance to radiation through combined effects of 
selection and radiation-induced variants. Most 
of the mutations, however, will be lethal, and 
development of radiation resistance has not 
yet been demonstrated (35, 36). Nevertheless, 
doses for commercial application must con- 
tain a margin of safety to insure complete 
sterilization. A dose of 16,000 rads has been 
recommended as adequate for granary weevils 
(38), flour beetles (13, 39), lesser grain borers, 
and cigarette beetles (111), but somewhat 
higher levels of exposure may be required for 
the Indian-meal moth and tropical warehouse 
moth (111). Moth species were also found more 
resistant than beetles and weevils to electron 
irradiation from a 1-Mev., peak, electron 
182 
beam generator (106). Many other studies of 
lethal doses of ionizing radiation for insect 
species have been reported (6, 7, 37, 44, 45, 
70, 117, 162). These 
~ Studies of botanical effects of electron ir- 
radiation on wheat seed showed that doses 
of 10,000 to 200,000 r.e.p. did not prevent 
germination, but wheat receiving 40,000 r.e.p. 
or more suffered drastic reduction in emer= 
gence from soil, and plants that emerged died 
soon thereafter (126). Radiation doses of the 
level required for insect sterilization were 
detrimental to early growth. Differences in 
baking quality were detected due toirradiation 
of wheat at higher exposures in this range, 
but were so slight that they would not be 
detectable using a commercial baking pro- 
cedure (103), Other studies have also shown 
that ionizing radiation of the levels required 
for insect control would be satisfactory as 
far as milling and baking quality are concerned 
(8, 25, 33, 40, 79, 98). 
Since ionizing radiations are so effective 
for controlling insects, and required radiation 
doses are not harmful to grain for consumptive 
use, practical applications have been seriously 
considered. The U.S. Food and Drug Adminis- 
tration has approved wheat irradiation for 
absorbed doses of 20,000=50,000 rads with 
gamma sources, providing energies of not 
greater than 2.2 Mev. (159). Electron irradia- 
tion of energies not greater than 5 Mev. is 
currently being considered for FDA approval 
(158). 
“Costs for gamma-radiation treatment to 
disinfest grain using Co-60 have been esti- 
mated in England (34, 36) at 3s. per ton for 
continuous operation (37 cents per U.S. ton at 
$2.80-per-pound sterling exchange rate). This 
exceeds costs for conventional chemical fu- 
migation, but costs of gamma sources are 
expected to decrease (35), and preliminary 
cost data on high-capacity electron acceler- 
ators appear promising for commercial treat- 
ment of grain (36). 
Studies of gamma irradiation of citrus 
fruit also showed that low doses of radia- 
tion were effective in controlling eggs and 
larvae of the Mexican fruit fly (Anastrepha 
ludens (Loew)) (27). The FDA is also con- 
sidering approval of gamma irradiation for 
citrus (158). 

