In the grasshopperValanga nigricornisa fusion between two telocentric autosomes, M8 and M9, is described which reduces significantly the chiasma frequencies of both the large and the medium members of the chromosome complement. This reduction was observed relative to both the normal spermatocytes within the single mutant individual as well as those in normal individuals from the same population sample. The meiotic behaviour of the fusion trivalent results in 50 per cent balanced gametes due to the random nature of its orientation at first metaphase of meiosis.