Role of the corpora allata and juvenile hormone in the control of imaginal diapause and reproduction in three species of locusts

Abstract

To understand the hormonal regulation of imaginal diapause and ovarian development in three species of locusts, Nomadacris succincta, Nomadacris japonica and Locusta migratoria, juvenile hormone (JH) biosynthesis by the corpora allata (CA) in vitro and JH esterase activity in the hemolymph were measured. The two species of Nomadacris exhibited a positive correlation between oocyte growth and JH biosynthesis by CA in vitro, although the correlation was significant only in N. succincta. In contrast, L. migratoria showed a negative correlation, indicating a higher rate of JH synthesis associated with more suppressed ovarian development. In this species, however, the hemolymph JH titer was higher in reproductively active females than in sexually immature females, indicating a positive correlation between the hemolymph JH titer and ovarian development. The levels and temporal pattern of variation in mean hemolymph JH esterase activity were rather similar between reproductively active and inactive females in L. migratoria. It is thus unlikely that the hemolymph JH esterase plays an important role in the regulation of the hemolymph JH titers in this species. Topical application of 100 μg of methoprene stimulated ovarian development significantly in L. migratoria, whereas 450 μg failed to induce ovarian development or vitellogenesis in sexually immature females of N. succincta and N. japonica. Besides JH, there appear to be other factors present that are involved in the control of the termination of diapause in the two Nomadacris species.