The transmission rates of the three main types of B chromosome present in the grasshopper Eyprepocnemis plorans were studied by two different methods: (i) cytological observation of their meiotic behavior in males and females and (ii) karyological analysis of the embryo offspring obtained either from gravid females collected in the field or from controlled crosses. We conclude that Bs are inherited in a random manner with no tendency toward accumulation or loss from either sex. The possible factors that might be responsible for the maintenance of this widespread polymorphism are discussed.

Mitotic instability of B chromosomes has been studied in males and females from two Spanish populations of Locusta migratoria. This instability is a common feature in embryos, adult somatic tissues such as gastric caeca, and ovariole wall cells and male and female germ lines. While B chromosomes accumulate in the male germ line independently of the existence or absence of intraindividual variation in the number of B chromosomes in gastric caeca cells, they do not accumulate in the female germ line despite meiotic instability. The relationship between the mitotic instability of the B chromosomes in germ lines and their mode of transmission is discussed.Key words: Locusta migratoria, B chromosomes, mitotic instability, accumulation.

HENRIQUES-GIL, N., G. H. JONES, M. I. CANO, P. ARANA, and J. L. SANTOS. 1986. Female meiosis during oocyte maturation in Eyprepocnemis plorans (Orthoptera: Acrididae). Can. J . Genet. Cytol. 28: 84-87The progression of meiosis from metaphase I to telophase I1 was followed in oocytes of Eyprepocnemis plorans that were dissected from mature females and maintained in saline solution. The durations of the various meiotic stages were assessed at three different temperatures.

Chiasma frequencies and distributions were compared in males and females, with and without different types of B-chromosomes, from four Spanish natural populations of Eyprepocnemis plorans. Mean cell chiasma frequency and mean autosomal chiasma frequency were substantially and significantly lower in females than in males. Females also showed altered chiasma distributions compared with males, with fewer proximal chiasmata and more interstitial and distal chiasmata. A variety of sex differences in meiotic chiasmata have now been described in the Orthoptera and these are compared and discussed. B-chromosomes had no effects on mean chiasma frequency and relatively little general effect on chiasma distribution, although some minor effects of B-chromosomes on chiasma distribution were detected in certain populations and classes of bivalents. In some of these cases B-chromosomes affected chiasma distribution in females but not in males.

An accumulation mechanism of the standard B chromosome of the grasshopper Heteracris littoralis has been studied in a natural population located in El Saler (Valencia) by two different methods: (i) the karyologica]l analysis of the offspring from wild females and (ii) cytological observations of male and female meiosis. The transmission rate of the accessory through females obtained from crosses (0.61) was slightly lower than that obtained from direct meiotic observations of secondary oocytes (0.71). The B chromosome is transmitted at a rate of about 05 through lB males, the value expected from mendelian segregation. The implications of these findings are discussed and the parasitic nature of the B is proposed.