The inheritance of radiation induced semi-sterility in Rhodnius prolixus

Eggs from crosses of 40 adult male R. prolixus irradiated with 6K rad -rays with normal females had a mean fertility of 23.9%, only 2 crosses being completely sterile. The 86 F₁ progeny of both sexes, when outcrossed with normal mates, had a mean egg fertility of 12.6%, and 43 of these matings were completely sterile. Twenty-eight F₂ bugs reared from F₁ x normal crosses were mated with normal partners and had a mean fertility of 44.6%, 6 of them being fully fertile, a reversal towards normal fertility. Cytogenetic examination of F₁ F₂ and F₃ males showed that these changes in fertility correlated well with the degree of chromosomal abnormality found. The very high recovery rate of translocations in F₁ generation males can be related to the holocentric chromosomes of these bugs which precludes the formation of dicentric chromosomes which are inviable in monocentric species. In F₁ and F₂ males the majority of translocations were associated as chains of III+I or as chains of IV. Only one bug was found with a ring of IV chromosome association and it is suggested that chromosome morphology, combined with a low chiasma frequency, favours chain association. Most chain multivalents showed linear orientation which may lead to duplication deficiencies and zygotic death. However parallel, indifferent and the more stable convergent modes of chain orientation were also all observed indicating that survival of some translocations in this species may be possible. The survival to the F₂ generation of chromosomal fragments confirmed the holocentric nature of triatomine chromosomes. It is suggested that semi-sterile males would prove more effective than releases of completely sterile males for reducing wild populations of R. prolixus, because of the delayed effects of sterilizing radiation consequent upon the holocentric structure of triatomine chromosomes.