Neurosecretory system and retrocerebral endocrine glands of Metochus uniguttatus Thunb. (Heteroptera: Lygaeidae)

Abstract

This paper deals with the neurosecretory system and retrocerebral endocrine glands of a lygaeid bug, Metochus uniguttatus Thunb. as revealed by whole mounts and histological sections, using the paraldehyde fuchsin (PF) and the performic acid victoria blue (PAVB) techniques. In the pars intercerebralis of the protocerebrum in M. uniguttatus are found only the A-type of medial neurosecretory cells (MNC), which occur in 2 groups, each group consisting of 9 cells. The MNC in the nymph shows small amount of neurosecretory material (NSM). The newly-moulted bugs either lack or show small amount of this material, which increases with the aging of the insect. About 6 days after the final moult, the cells are filled with a moderate amount of NSM. The lateral neurosecretory cells have not been observed. The NSM synthesized in the MNC is transported to the aorta dorsalis (AO) via neurosecretory pathways (NSP) and nervi corporis cardiaci —I (NCC—I) and is stored in 2 regions: (i) the swollen end of NCC—I (BS), and (ii) the aortic wall itself. From the latter it is presumably released finally into the blood. The axons of the 2 groups of MNC constitute the 2 neurosecretory pathways that decussate on the dorsal side of the photocerebrum. The 2 pathways, after the crossover, run into the proto- and deutocerebrum, and emerge from the tritocerebrum as NCC—I. The axons of NCC—I of each side end in a bulbous swelling (BS) in the aorta. From the latter a number of secondary axons arise and terminate in the aorta dorsalis at different levels. The aorta consists of 2 layers of loose tissue the inner layer (IN) of which is the thick and the outer (OT) is thin; the latter is devoid of NSM. The NCC—II are short nerves that originate from the tritocerebrum and end in the corpora cardiaca (CC) of the ipsilateral side. The CC are 2 spherical bodies that lie below the aorta. The CC consists of 2 types of cells. The corpus allatum (CA) is oval, lying below the aorta and is placed behind the CC. The CC and CA lack NSM. The cells of the CA in immature stage contain a little of the secretory material but plentiful in mature forms. The suboesophageal ganglion (SOG) contains 2 A-cells. It has been suggested that the MNC of the protocerebrum and NSC of SOG are identical in staining patterns and their carrier proteins, i.e. rich in cystine and/or cysteine.