The inheritance of radiation induced semi-sterility in Rhodnius prolixus

Eggs from crosses of 40 adult male R. prolixus irradiated with 6K rad gamma-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 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, "parellel", "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.