GENETICS OF SEX DETERMINATION IN THE HESSIAN FLY, MAYETIOLA-DESTRUCTOR

Individual females of the Hessian fly, Mayetiola destructor (Say), produce four types of progenies: (1) all female progenies, (2) all male progenies, (3) predominantly female, bisexual progenies, and (4) predominantly male, bisexual progenies. Based on experimental results, a genetic model involving a single maternal-effect, autosomal gene (Chromosome maintenance, Cm) was constructed to explain the occurrence of the four progeny types. Selection for lines of Hessian flies that were either monogenous or bisexual indicated that these characteristics were heritable. Matings between females and exceptional males within the monogenous line indicated that the type of progeny produced depends on maternal genotype and that exceptional individuals result from sex-chromosome nondisjunction during oogenesis. Reciprocal matings between the monogenous and bisexual lines indicated that alleles responsible for sex-chromosome maintenance segregate in a simple Mendelian fashion and have primarily a maternal effect. The genetic model proposes that sex is determined by a ratio between sex chromosomes and autosomes that is established during embryogenesis by the maintenance or elimination of the paternally derived sex chromosomes. This behavior is conditioned by three types of alleles operating at the Cm locus.