Viability and Sex Determination in the Honey Bee (Apis Mellifera L.).

FTER WHITING (1940a, 1943) established conclusively that sex in the A parasitic hymenopteron Habrobracon is controlled by multiple sex alleles, it became of interest to determine whether the same mechanism exists in other insects, in which males develop from unfertilized eggs and are haploid. The work described in this paper was started in 1944 at the SOUTHERN STATES BEE CULTURE LABORATORY, of the BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE, to determine whether sex is controlled by the same mechanism in the honey bee. In this insect the problem was also of practical interest because it involved egg hatchability, which is of vital importance in the building up of colony pomdations for honey production. According to WHITING, sex in Bracon hebetor Say2 is controlled by a series of sex alleles (xu, xb , xc, etc.). Females are heterozygous ( x a / x b , xa /xc , etc.), and when unmated produce haploid sons of two types in equal numbers (xu and xb , xu and xc, etc.). When females are mated, about twothirds of their eggs are fertilized. If the parents have different sex alleles (xu/xb x xc, for example), all fertilized eggs develop into females (xu/xc and x b / x c ) . This is called a three-allele fraternity. If one of the sex alleles of the female parent is identical with that of the male parent (xu/& x xu for example), then one-half the fertilized eggs are heterozygous (xu/&) and develop into females, and one-half are homozygous (xayxa) and highly inviable but sometimes develop into adult biparental males. This is called a two-allele fraternity. Haploid males are highly viable. Inbreeding tends to bring together identical sex alleles, resulting in low viability, whereas in outcrosses such combinations are less likely and good viability usually occurs. WHITING has already demonstrated nine alleles, and there are probably many more present in the wild population. Their allelic nature has been demonstrated by linkage tests. Although Bracon hebetor is the only species in which the existence of multiple sex alleles has been proved, genetic work suggests that the sex-determining mechanism is the same in other members of the genus and in other Hymenoptera in which outcrossing is common. In B. brevicornis Wesmael, SPEICHER and SPEICHER (1940) found biparental males. INABA (1939) has