The cephalic and prothoracic skeletomusculature and nervous system in Lethocerus (Heteroptera, Belostomatidae)

Abstract

The head of Lethocerus, unlike that of many Hyclrocorisae, does not vary extensively from the t,ypical heteropteran cephalic plan. Its skelrt,otilusculature is here described, a n d the possible derivation of some cephalic structures is discussed. Lethocerics is large enough to permit a t l~. tailed examination of such features as the salivary pump, the labial holdfast, and the opening of the maxillary gland. Of special interest, are ( I ) the possible persistence of anterior tentorial pits and an epicranial suture in the adult, ( 2 ) peculiarly shaped antennae, conctdcd in clorne-like subocular invagination of the exoskcleton, and (3) the presence of filt.ering devices in the cibarial food pump.The predatory forelegs are enlarged, with a powerful musculature and complex inncrvation. To provide sufficient surfaces for the attachments of their extrinsic muscles, and skelrtal support against the pull of these muscles, the prot,horax of Lethocerus is more modified than that of most other Heteroptera. Tho pleural ridge is enlarged and fused with t h r tergurii, and the rim of the coxal cavity is strengthenrd and elevated, bracing the dorsal exoskeleton. The supracoxal lobes have fused dorsally antl a p p a r to form a part of the dorsal prothoracic exoskeleton; they conceal the pleural sulcus cxtrrnally.The anterior three ganglia (brain, suhesophagcal ganglion, and prothoracic ganglion) of t,hr central nervous system are closely joiocd, antl arc widely separated from tho fuswl pterothoracic and abclominal ganglia. The (list rihut,ion of the nerves from these thret. ganglia within the head, prot,horax, and prothoracic 1r.g is lirre described. The external Etppriwaticr of the corpora allata and cardiaca is briefly tliscwssctl. These endocrine glands arc rlo associated with the aorta and resemble, a t lcwst sul)erficially, those previously clrs(.ril)r other Hydrocorisae.The availability, hardiness, and large sim of Lcllrocrrus make i t n convenient subject for iiiorphological and physiological studies. A f t v suggestions for future research on tliis 11 are here presented. CONTEKTS330 33 1 351 351 354 354 357 357 359 361 362 363 364 36.5 366 368 Skeletovnusculature and nervous system in Letliocerus 351 11. MATERIALS AXD METHODSAll observatioiis were made on preserved, atliilt specimens of two species, Lethoc ems uhlerr (Montandon) and L. griseus (Say); a laigcr number oftlie former tliaii of the latter \$ere used. The insects ranged froin 45 to ($0 mni in length, speciinens of L. gtiserc.9 tciitlmg t o be somenhat larger than tliosc of L. uhlrri Except for skeletal differences iii the forelegs. tlie cephalic and prothoracic anatomy \\ as essentially identical in the tu o .;pecie'The specimens, preserved i n Bouin's fluid or 10'i(l formalin, 11 ere obtained froin l+)ri(la The most satisfactory results were achievcd fi om insects which \\ere specially pi cpti c d to ensure adequate penetration of the fixative; before fixation one coinpoimtl e> e \i cut off a i d the abdomen mas slit open along o i i~ d e Specimeiii preser...

Evolutionary Trends in Heteroptera. Part II. Mouthpart-Structures and Feeding Strategies

“…Such a ring occurs in Nepomorpha and PARSONS (1969a) suggested that a pull on the tendon would flatten this ring, causing the intercalary sclerites to come together and thus restrict movements of the stylet bundle. The same author examined labial structures in representatives of Ochteridae, Gelastocoridae, Nepidae, Belostomatidae, Notonectidae and Naucoridae (PARSONS, 1959(PARSONS, ,1966b(PARSONS, , 1968(PARSONS, ,1969a. She stated (1969, p. 298) that in all Nepomorpha thus far examined, a holdfast mechanism was present similar to that in Aphelocheirus, but that some possess only the muscle and sclerotized ring and not the intercalary sclerites.…”

“…Large taxa lacking a lever are: Gerromorpha, Reduvioidea, and Enicocephalomorpha (only a few species examined). In Nepomorpha it is said to be absent in Nepidae, Belostomatidae, Corixidae, Gelastocoridae and Notonectidae (NEISWANDER, 1926;HAMILTON, 1931;Burr, 1943;QUADRI, 1951;BENWITZ, 1956;PARSONS, 1959PARSONS, , 1968. PARSONS (1959PARSONS ( , 1966 established its presence in Gelastocoridae and in two of seven naucorid genera.…”

“…PARSONS (1966bPARSONS ( , 1968PARSONS ( ,1969a found the median, bifurcate, tendon of the third segment to be present in representative Ochteridae, Gelastocoridae, Nepidae, Belostomatidae (with paired tendons! ), Notonectidae, and Naucoridae, but not in the deviant Corixidae.…”

“…Generally, the tendons form a single uniform row, as in Nepidae and Belostomatidae, but other Nepomorpha reveal subdivisions of different types ( Fig. 14; PARSONS, 1959PARSONS, , 1966aPARSONS, , 1968PARSONS, ,1969.…”

“…This term, used for the two dorsal plates at the base of the fourth rostral segment of Nepomorpha (PARSONS, 1959(PARSONS, , 1966b(PARSONS, , 1968(PARSONS, , 1969a, is not quite appropriate for most Gerromorpha (Hebridae, Mesoveliidae, Hydrometridae). Here, they form a thin, cuticular layer around the whole rostral circumference, separated into two dorsal and two ventral flaps.…”