Effects of Temperature on Fertilization in Habrobracon.

N THE parasitic wasp Habrobracon juglandis (Ashm.), when a cross of I unrelated stocks is made, males (haploid) come from unfertilized eggs and females (diploid) from fertilized eggs. When the parental stocks are closely related, not only males from unfertilized eggs but also males (diploid) from fertilized eggs appear. That such biparental males should be produced was puzzling until WHITING brought forth his theory of sex determination in the Hymenoptera (1933a, 1933b, 1935). According to this theory females have the sex chromosomes X and Y, while haploid males have either X or Y and biparental males either two X's or two Y's. One might then expect equal numbers of biparental male and female offspring according to the principle of random fertilization. However the number of biparental males is always much smaller than that of the females. This deviation from equality WHITING has explained in part by differential mortality, in part by differential maturation. When parental stocks are unrelated differential maturation is complete, all zygotes being XY and resulting in females only. Due to the greater viability of females in contrast to that of diploid males, hatchability of eggs and viability of offspring is much greater when parents are unrelated. This greater fecundity together with lack of biparental males, necessitates the supplementary hypothesis of differential maturation. It has already been shown (WHITING and ANDERSON 1932) that temperature also affects the production of biparental males among progeny from crosses of related stocks. A much higher percentage of males among biparentals was produced when mothers were set a t high temperature (3oOC) than at low (2ooC), while the percentage of biparentals, males and females, among total offspring was decreased. After BOSTIAN (1934) produced an orange-eyed stock (I 1-0) closely related by grading to a certain wild-type stock (11) and giving very high percentages of males among the biparentals, it was shown (ANDERSON 1935) that if stock 11 males were reared a t different temperatures (20°, 30°, 36°C) even though the stock 11-0 females were kept a t constant temperature (3ooC), significant differences appeared in percentages both of males among biparentals and of biparentals among total offspring. In this case