Supernumerary chromosomes in the human bed bug,Cimex lectularius Linn. (Cimicidae:Hemiptera)

The chromosome complement in the human bed bug, Cimex lectularius Linn., is 26+X₁X₂Y in the male and 26+X₁X₁X₂X₂ in the female. However, a population from Cairo, Egypt has 4 supernumerary X chromosomes. In the hybrid between the Berkeley population (with no supernumeraries) and the Cairo population (with 4 supernumeraries), the behavior of supernumeraries was observed during embryogenesis and oogenesis as well as spermatogenesis.In embryogenesis the transmission of supernumeraries was quite regular. However, one chromosome may sometimes be eliminated early in the germ line. This abnormality could induce the variations in chromosome number encountered in later stages. In the first meiotic division, some of the supernumeraries were nondisjunctional. Moreover, in the second division, some supernumeraries were eliminated. These results show that there is a tendency towards a decrease in the number of supernumeraries in the hybrids.Although the supernumeraries behave like X chromosomes, they seem not to be important for sex determination and appear to be largely or entirely inert genetically. Supernumeraries in the bed bug originate from small fragments caused by structural rearrangement. They are increased by an accumulation mechanism. Supernumeraries in the bed bug appear to be of relatively recent origin. The phylogenetic sequence in their development was probably from none to a stabilized number of four in the Old World. Then the supernumeraries were lost in two specialized lines, Cimex columbarius Jenyns on domestic birds in Europe and Cimex lectularius Linn. on man in the Western Hemisphere.This study was carried out under U.S. Public Health Service Grant (GM-13197).