EFFECT OF SUBSTERILIZING DOSES OF RADIATION ON SPERM PRECEDENCE IN FALL ARMYWORM (LEPIDOPTERA, NOCTUIDAE)

The effect of radiation on sperm priority and mixing patterns in the f all armyworm, Spodoptera frugiperda (J. E. Smith), was studied by sequ entially mating females with irradiated (100 and 150 Gy) and normal ma les. Progeny of irradiated males were identified by visible chromosoma l aberrations in the testes. Twice-mated females produced more progeny fathered by irradiated males when irradiated males received a 100-Gy dose than when males received a 150-Gy dose, and exhibited incomplete last-male sperm precedence with extensive sperm mixing. Mating sequenc e had no significant effect on the number of oviposition days in which sperm mixing occurred. Also, the day of oviposition (days subsequent to the last mating) had no significant effect on sperm priority and mi xing patterns. However, when females exhibited sperm mixing, the mean percentage of progeny fathered by irradiated males was significantly h igher when males were irradiated with 100 Gy than when males were irra diated with 150 Gy. Sperm complements from males irradiated with 100 G y were successfully competitive with sperm complements from normal mal es, but there was a reduction in sperm competitiveness from males irra diated with 150 Gy.