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Abstract -73- This work is a st~dy on the effects of gamma irradiation uponreproductlon and mating competitiveness of t~t \:~(. sugar cane stem borer Sesam1a cretioa and Jl cotton leaf worm Spodoptera 11ttoralis.Six doses of gamma radiation, 10, 15, 20, 25, 30 and 35 krad were used for -S. cretioa, while three doses 20, 35 and 50 krad were used for .S--•. littoralis. These studies continued throughout two year 1981 - 198). The following are the main results obtained; 5-1. Sugar cane stem borer S. cretica I 1) When adult moths, less than 24 ho~s old, were exposed to 10, 15, 20, 25, 30 and 35 krad, the fecundity of the females decreased, almost proportionally, with the increase in the dose. 2) The treatment of the male had 11ttle effeot on tie fecundity of the female • ) The reduotion in egg viability, of the sugar cane borer , was highly oorrelated with the given dose. 4) At the same dose irradiated temales laid more nonviable eggs wben paired with untreated males than wben untreated females were mated With irradiated males. --- - - -,--- ---- -- --- -_. ----- _ .. - --- --_. _._- ._- - .,,-_. - 74 - 5) Sterilizing dos8 fJr adult females was 30 krad, while 35 krad was the sterilizing dose tor adult males. 6) There was a significant reduction in the percentages of egg-hatching within all ratio combinations including treated males and temales as compared with the untreated control combinations. 7) Neither theperecentage of mated females, nor the average nl.1mberof spermatophores per mated female got affected by irradiating the adult moths with 10, 15, 20 or 25 krad. 8) A:t 30 or 35 krad the percentage of mat.ed females having sperm in their spermatheoae was significantly less than 1n those subjected to 10. 15, 20 or 25 krad doses. 9) Gamma rays, till 35 krad had almost no effect on adl.11tlongevity of both sex. 10) The male competitiveness value was higher • among-the males or females irradiated With 35 krad. 11) The reduction in egg hatch was signit~cantly greater at the ratio 5:111 than at 1:1:1. (treated males: untreated male : Wltreated temale). -- -- - - ._- -’- --- - ------ - ------ -- ~~~ ~---,_._.-~-- -- -- - - 76 - 8) Ad~lt males or ad~lt females irradiated with 20t 35 and 50 krad did not affect the ability of sperm transfer in the spermathecae. However, at 35 krad the percentage of irradiated· ••ted females having sperms significantly less than untreated control. 9) Gamma rays lBd al~ost no effect on adult longevity except females receiving 35 krad which lived significantly longer period than untreated ones. 10) Increasing the ratios of either irradiated males or irradiated females to eated population from 1:1:1 to 5:1:1 gave significant1 more reduction in egg hatch. 11) The competitiveness v lues were significantly higher for the males or the fe les irradiated with 50 krad. 12) A significant reductio in egg batch occured within the combinat1onsof native ama1e paired with laboratory male than native female pa red with native mAle. 13) Irradiation of labors ory maleswlib substeriJ!z1JJgdoses of 20an4 35kard lead to good co etitivene88 with the native males, 1n mating With native fa las. In the meantime t the reduction in egg hatch 1n 1:1 combination was significantly more than in the - 77 14~A oomplete sterility we obtained when adult (less than one day - old) irradiated t 50 krad for females and males. |