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

Magdalena Hodková,Radomír Socha

doi:10.14411/eje.2006.068

Abstract

Mechanisms of the suppression of gonadotropic activity of the corpus allatum (CA) in females were com- pared with those previously reported for either or non-diapause females by reciprocal transplanta- tions 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 non-diapause 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 non-diapause females. On the other hand, the CA of females is of intermediate size between that of the feeding non-diapause and females, similar to the CA of the non-diapause 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 wing- polymorphic species of insects.

Highlights

The firebug, Pyrrhocoris apterus (L.), has two wing morphs: long-winged and short-winged (Socha, 1993)
The neuroendocrine complexes of BR-SG-CC-corpus allatum (CA) were transplanted between macropterous and brachypterous females, both kept under long days
The BR-SG-CC-CA from long-day brachypterous females stimulated reproduction in more than three quarters of long-day brachypterous females within 24 days, while only less than one-third of recipients was stimulated by the complex from macropterous females within the same period (Fig. 1) and only slightly more than one-third of recipients started oviposition within the 50-day experiment (Table 1, B vs. D)

Summary

Introduction

The firebug, Pyrrhocoris apterus (L.), has two wing morphs: long-winged (macropterous) and short-winged (brachypterous) (Socha, 1993). Vitellogenesis is inhibited under long days in the absence of food (Hodková, 1982) In both long-day starving and short-day diapause females, the activity of the corpus allatum (CA) is inhibited via nervous connections with the pars intercerebralis of the brain, but the inhibitory mechanisms are different (Hodková, 1976, 1977a,b,c, 1979, 1982, 1992; Hodková et al, 2001). Different levels of the CA inhibition are indicated by more advanced growth of pre-vitellogenic oocytes in starving long-day females than in short-day females. This difference is most probably caused by a higher activity of the CA in the former case; the ovaries of allatectomized females have “diapause” appearance irrespective of food conditions (Hodková, 1999). The CA of short-day females is smaller compared to starving long-day females (Hodková, 1999)

Methods

Results

Conclusion