Annual cycles in the incidence of b chromosomes in the grasshopper Myrmeleotettix maculatus (acrididae: orthoptera).

The frequency of B chromosomes has been determined for several stages in the grasshopper life-cycle, over three generations, in three natural populations spanning a steep cline in East Anglia. This has revealed a rise in B frequency in prediapause eggs, a fall during the winter in the embryos and a rise in the early nymphs in certain situations. The causes of these effects are discussed and also their importance, along with meiotic drive, in maintaining an environmentally correlated cline of stable adult B frequencies.