The genetics of hybrid sterility between subspecies of the complex ofGlossina morsitansWestwood (Diptera: Glossinidae)

Abstract

AbstractCrosses were made between the three subspecies of the complex ofGlossina morsitansWestwood and the hybrid females backcrossed. Hybrid female fecundity was highly ‘reactive’ to foreign male genes when the mother wasG. morsitans centralisMachado compared with the reciprocal crosses and backcrosses. Hybrid F1males were unable to inseminate females successfully, and although in nearly a quarter of the dissections sperm was transferred to the uterus, it did not migrate to the spermathecae. Heterozygosity between the X- and Y-chromosomes and most of the autosomes led to high frequencies of sterile males, but homozygosity between the X- and Y-chromosomes could still yield 30–50% sterility. Successive backcrosses of hybrid females betweenG. m. morsitansandG. m. centralisto the latter subspecies continued to increase the frequency of fertile males. Interactions between X-chromosome and autosomal gene seemed to be responsible for hybrid male sterility, and the number of sterility genes involved appeared to be very few. Crosses involvingG. morsitans submorsitansNewstead generally agreed with those between the other two subspecies, but the distortion in the sex ratio of emergent adults limited the application of the data to this subspecies. Competition experiments using sterile hybrid males and fertile males in population cages (30 cm cube) showed that suppression was possible, especially when the ratio of sterile:fertile males was 2:1. The value of stetile hybrid males in tsetse control programmes and the evolution of reproductive isolation in the complex is discussed.