CYTOLOGICAL AND DEVELOPMENTAL ANALYSIS OF TYCHOPARTHENOGENESIS IN LOCUSTA-MIGRATORIA

A number of females of Locusta migratoria have shown tychoparthenogene tic reproduction (a kind of accidental thelytoky) characterized by: (i ) a female-biased primary sex ratio; (ii) the production of embryos wi th abnormal ploidy levels, mainly haplodiploid mosaics; (iii) a longer time for embryo development; and (iv) the capability of producing fem ale offspring that reproduced in the absence of males. Perfect diploid ization is not essential for parthenogenetic embryos to reach the adul t stage but a great majority of embryo cells must be diploid to comple te properly embryogenesis and hatch. In addition, diploidy is apparent ly necessary to the ovary of parthenogenetic females so that eggs laid without mating can hatch. Cytological analyses of embryos at differen t developmental ages have shown that parthenogenetic embryos begin hap loid and gradually become diploid, thus passing through a haplodiploid mosaic stage. The most likely mechanism for ploidy restoration is the restitution of the sister products of cleavage mitoses, although our results show that cell fusion could be another mechanism, the relative importance of which remains to be tested in future work. Although par thenogenetic females showed a fecundity comparable to that of sexual f emales, their reproductive output was significantly lower because of a decrease in the number of embryos per pod and a consequent decrease i n the rate of embryo production.