Endocrine regulation of the reproductive arrest in the long-winged females of a flightless bug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

Abstract

Abstract. Mechanisms of the suppression of gonadotropic activity of the corpus allatum (CA) in macropterous females were compared with those previously reported for either diapause or starving non-diapause brachypterous females by reciprocal transplantations of the neuroendocrine complexes (comprising the brain-suboesophageal ganglion-corpora cardiaca-CA). The denervated CA stimulated reproduction in most females of all experimental groups suggesting an inhibition of the CA via nervous connections with the brain. The inhibition of the CA within the transplanted neuroendocrine complex was measured by the reproductive performance of feeding recipient females deprived of their own CA. The complex from starving non-diapause brachypterous females stimulated reproduction in 58.3-78.9% of recipients suggesting that the inhibition of the CA was mostly overcome by the stimulating internal milieu of feeding females. In contrast, the "macropterous" complex stimulated reproduction in only 18.8-37.5% of recipients, similar to the "diapause brachypterous" complex (32.0%). The results indicate that the "macropterism", similar to the diapause, is associated with a considerably lower responsiveness of the neuroendocrine complex to humoral stimulation by feeding compared to the responsivenes of the "starving" complex from brachypterous non-diapause females. On the other hand, the CA of macropterous females is of intermediate size between that of the feeding non-diapause and diapause brachypterous females, similar to the CA of the non-diapause brachypterous females deprived of food. Overall, the data suggest that the suppression of the CA activity results from a combination of the diapause-like refractoriness of the neuroendocrine complex with the starvation-like inhibition of the CA growth. Regulation of the CA activity is discussed in relation to the "oogenesis-flight syndrome" recorded for flying wingpolymorphic species of insects.

Factors terminating ovarian arrest in long-winged females of a flightless bug, Pyrrhocoris apterus (Heteroptera: Pyrrhocoridae)

“…However, the results accord with the knowledge that both the synthesis of vitellogenin and growth of vitellogenic ovaries in P. apterus are JH-dependent processes (Socha et al, 1991 and associated with large size and high activity of the CA (Hodková et al, 2001). The activity of the large CA of long-day reproductive brachypterous females with vitellogenic ovaries is about four times higher than that of the smaller CA of starved long-day brachypterous and spontaneously fasting long-day macropterous females with pre-vitellogenic ovaries (Hodková et al, 2001, Hodková & Socha, 2006. The activity of the CA in young long-day macropterous females is inhibited via nervous connections from the brain (Hodková & Socha, 2006) as in short-day diapausing and long-day starving brachypterous adult females of P. apterus (Hodková, 1976(Hodková, , 1977(Hodková, , 1982, which also show inhibited growth of vitellogenic ovaries.…”

“…The activity of the large CA of long-day reproductive brachypterous females with vitellogenic ovaries is about four times higher than that of the smaller CA of starved long-day brachypterous and spontaneously fasting long-day macropterous females with pre-vitellogenic ovaries (Hodková et al, 2001, Hodková & Socha, 2006. The activity of the CA in young long-day macropterous females is inhibited via nervous connections from the brain (Hodková & Socha, 2006) as in short-day diapausing and long-day starving brachypterous adult females of P. apterus (Hodková, 1976(Hodková, , 1977(Hodková, , 1982, which also show inhibited growth of vitellogenic ovaries. Termination of nondiapause type of ovarian arrest and egg development in older (> 14 days old) long-day macropterous females of P. apterus after resumption of feeding is most probably the result of the increased volume of their CA (Hodková & Socha, 2006) and resultant higher JH titre stimulating the growth of vitellogenic ovaries.…”

“…The activity of the CA in young long-day macropterous females is inhibited via nervous connections from the brain (Hodková & Socha, 2006) as in short-day diapausing and long-day starving brachypterous adult females of P. apterus (Hodková, 1976(Hodková, , 1977(Hodková, , 1982, which also show inhibited growth of vitellogenic ovaries. Termination of nondiapause type of ovarian arrest and egg development in older (> 14 days old) long-day macropterous females of P. apterus after resumption of feeding is most probably the result of the increased volume of their CA (Hodková & Socha, 2006) and resultant higher JH titre stimulating the growth of vitellogenic ovaries. Stimulation of the CA by feeding also occurs in long-day brachypterous females (Hodková, 1982(Hodková, , 1992.…”

“…Unlike the de-alated macropterous females of P. apterus, de-alation of the cricket Velarifictorus parvus at adult emergence did not influence the length of the pre-OP (Tanaka, 1991). However, accelerated termination of ovarian arrest in the long-day macropterous females of P. apterus was observed when they were injured in different ways (Hodková & Socha, 2006). The injury signal is transmitted to the neuroendocrine complex via the nervous system (Hodková & Socha, 2006).…”

“…The growth of vitellogenic oocytes in long-day brachypterous females of P. apterus is a JH-dependent process (Socha et al, 1991) depending on the full activity of the corpus allatum (CA) -the source of juvenile hormone (JH) (Sláma, 1964). The non-diapause type of ovarian arrest observed in young long-day macropterous females is characterized by the presence of pre-vitellogenic ovaries (Socha & Šula, 1996;Hodková & Socha, 2006) and indicates that JH titre in the body of these females is below the threshold necessary for the growth of vitellogenic ovaries. Ovarian arrest is then spontaneously terminated in older long-day macropterous females, but what factors play a role in this termination is unknown.…”