Effects of Gamma Radiation on Codling Moth Eggs

Abstract

Radiation studies on eggs of the codling moth (Caxpocapsa pomonella) were initiated to learn if this approach might be used to influence response of the insect to insecticides. The radiation effects on hatchability, life history of the progeny through several generations, and susceptibility of the larvae to insecticides are reported. The eggs were exposed to Co/sup 60/ gamma radiation to establish a strain designated Va.-GR. Most of the eggs were four days old when irradiated. During each of the next four seasons the Va.-GR strain was reared through two generations on unsprayed apples. Principal effects on biological performance were; temporary increase in incubation period of the egg; increase in average number of eggs deposited by Va.GR females; and slight increase in longevity of Va.-GR moths. Sensitivity to gamma rays declined with aging of the eggs. Susceptibility to DDT and lead arsenate was not altered by irradiating eggs four days old, but an increase in DDT resistance followed irradiation of Va.-GR eggs less than one day old. Susceptibility to weak concentrations of Guthion (0,0-dimethyl-S-(4-oxo-1,2,3-benzotriazin-3(4H)- ylmethyl)phosphorodithioate) or Sevin (l-naphthyl-Nmethyl-carbamate) was not affected. Fortifying DDT with antiresistant compound did not influence resistance of Va.GR larvae to DDT. Adding Bakthane, a wettable powder containingmore » Bacillus thuringensis, to DDT did not eliminate the apparent difference between the strains in 1962 but in the case of the parent strain (Virginia) larvae toxicity was reduced. Inasmuch as the two strains were reared in the same manner on unsprayed apples and were subject to similar environmental factors, resistance to DDT by the Va.GR strain can be attributed only to selective action of gamma rays on young eggs; that is, eggs not exceeding 24 hr old. The same dosage on young eggs of the same brood did not select for resistance to weak concentrations of Guthion or Sevin insecticides. Selection for DDT resistance in the young eggs but not in eggs four days old may be explained by assuming that the cells from which the DDT-resistant mechanism is derived are more sensitive to gamma rays in the young eggs than in embryos that are formed. Duration of effects of selective gamma radiation on codling moth eggs is not known, but increased length of the egg stage appeared to be temporary. Such effects as increased egg production and increased longevity of the female moths were manifested through six generations. On the other hand, increased life span of the male moths was no longer evident in the sixth generation. (BBB)« less