Rhodnius Prolixus

R. Gary Chiang, Jennifer A. Chiang and K.G. Davey
Department of Biology, York University, M3J 1P3 North York, ON, Canada
Cell and Tissue Research. 1990 Volume 261, Issue 3, Pages 583 - 587.

Structure of the abdominal receptor responsive to internally applied pressure in the blood-feeding insect, Rhodnius prolixus.

The sensory receptor responsive to pressure applied internally to the ventral abdominal body wall of the blood-feeding insects, Rhodnius prolixus, is a single sense cell containing, at its distal end, a cilium enclosed within a scolopale, a densely staining structure characteristic of insect scolopidial sensilla.   A small spherical structure lies within a dilation near the midregion of the cilium, and contains nine heavily staining bodies, the position of each corresponding to a pair of microtubules in the cilium.   Proximal to the dilation, the microtubules are organized in a ring of nine pairs with one microtubule of each pair associated with dyneinlike arms.   Dastal to the dilation a central pair of microtubules is present, but dyneinlike arms are absent.   The scolopale cell, which gives risc to the scolopale, has cytoplasmic invaginations that form an elaborate array of extracellular compartments surrounding the body wall of the sense cell.   These compartments may serve to dampen high frequency vibrations permitting the receptor to respond to pressure exerted by touch, an attribute in keeping with the receptor's proposed function of detecting abdominal distension related to the size and movement of the stomach.


R. Gary Chiang, Jennifer A. Chiang and K.G. Davey
Department of Biology, York University, M3J 1P3 North York, ON, Canada
Journal of Morphology. 1990, Volume 204, Issue 1 , Pages 9-23.

Morphology of the dorsal vessel in the abdomen of the blood-feeding insect, Rhodnius prolixus.

The dorsal vessel (DV) in the abdomen of the blood-feeding insect Rhodnius prolixus was divided functionally into two regions, the heart, into which haemolymph entered the DV through four pairs of ostia located in abdominal segment VII, and the aorta, along which the haemolymph was propelled from abdominal segment VI to the thorax.   Osmium-fixed whole mounts revealed the DV to consist of spirally arranged striated muscle fibers and to possess two rows of ventrally attached longitudinal fibers extending the length of the abdomen.   Seven pairs of alary muscles were found attached to the DV in the posterior abdominal segments.   Contractions of the alary muscles attached to the ventral surface of abdominal segments VII and VIII served to expand the heart.   Electron microscopy revealed the DV to consist of a thin layer of contractile elements surrounded by an inner (intima) and outer (adventitia) connective tissue layer.   Embedded in the intima along each lateral side of the DV were two large groups of endocardial cells extending the length of the DV.   A small group of pericardial cells was embedded in the adventitia along the mid-ventral side of the DV, and clusters of pericardial cells were found attached to the alary muscles.   Nerve terminals were found only on the heart: they contained agranular synaptic vesicles approximately 30 nm in diameter and densely stained granules approximately 100-120 nm in diameter.   These structural components are discussed in relation to the role of the DV in circulation.


R. Gary Chiang, K.G. Davey, Jennifer A. Chiang, H.R. Khan, A.S. Saleuddin
Department of Biology, York University, M3J 1P3 North York, ON, Canada
Journal Neuroscience Methods. 1988 Volume 23, Issue 1, Pages 7-14.

Extracellular application of cobalt: a fast and simple method for delineating invertebrate neurosecretory pathways.

The extracellular cobalt backfilling technique was shown to be an excellent method to obtain cobalt backfills of invertebrate neurosecretory cells (NSCs).   Aqueous cobalt was placed in an extracellular suction electrode into which a portion of a neurohaemal (NH) region containing the axons and/or terminals of NSCs was drawn.   Spontaneously discharging extracellular action potentials were recorded as the cobalt was applied to the NH region, and the greater the electrical activity, the more extensive the cobalt backfilling.   The greatest success occurred with 0.5 M cobalt chloride dissolved in physiological saline. No backfills were obtained in the absence of electrical activity.   This technique was shown to backfill NSCs terminating in NH regions of the insect, Rhodnius prolixus, the isopod crustacean, Oniscus asellus, and the freshwater pulmonate snail, Helisoma.   Combined with a light insensitive silver intensification method, this paper describes a relatively fast and simple method for delineating invertebrate neurosecretory pathways.


R. Gary Chiang and K.G. Davey
Department of Biology, York University, M3J 1P3 North York, ON, Canada
Journal of Morphology. 1988, Volume 195, Issue 1, Pages 17-29.

Morphology of neurosecretory cells delineated with cobalt applied extracellularly to the cephalic aorta of the insect Rhodnius prolixus.

Cobalt applied extracellularly to the cephalic aorta in Rhodnius prolixus filled neurosecretory cells (NSCs) located in the brain, the retrocerebral complex, and the suboesophageal ganglion (SOG).   Axons of these cells converged over the corpora cardiaca and corpus allatum and merged into a large tract before travelling posteriorly along the ventral side of the aorta.   Cobalt-filled cells in the posterior margins of the brain and the retrocerebral complex lacked extensive dendritic arborizations, suggesting that their cell bodies and/or axonal processes in the retrocerebral complex are directly involved with integrative processes determining hormone release.   Cobalt-filled cell bodies in the anterior region of the brain were closely associated with the ocellar nerve, and the cobalt-filled cells in the SOG formed extensive dendritic arborizations in the neuropile, suggesting the involvement of sensory cells in regulation of their electrical activity.   The ability to fill NSCs with cobalt applied to the aorta demonstrates that the cephalic aorta of Rhodnius prolixus is an important neurohaemal region.


R. Gary Chiang and K.G. Davey
Department of Biology, York University, M3J 1P3 North York, ON, Canada
Science. 1988, Volume 241, Issue 4873, Pages 1665-1667.

Novel receptor capable of monitoring applied pressure in the abdomen of an insect.

A pair of receptors, responding tonically to pressure applied internally, occurs on the ventral body wall of abdominal segments two to five in the adult of the blood-feeding insect, Rhodnius prolixus.   These receptors are located in a region of the body wall subject to forces directly related to the size and movement of the stomach, an enlarged region of the midgut which stores the blood meal, and are therefore well suited for monitoring the degree of distension there.


Kenneth G. Davey and R. Gary Chiang
Department of Biology, York University, M3J 1P3 North York, ON, Canada
Archives of Insect Biochemistry and Physiology. 1989. Volume 11, Issue 3, Pages 139-146

The effect of severing the dorsal vessel on egg production in Rhodnius prolixus.

Severing the dorsal vessel (DV) behind the corpus allatum (CA), or in the anterior part of the abdomen of Rhodnius prolixus, greatly reduces egg production, an effect which is abolished by the topical application of juvenile hormone l (JH l).   Severing the DV in the posterior abdomen does not result in a marked reduction of egg production, although severing the alary muscles in segments V and VI has a similar effect to severing the DV in the anterior abdomen.   Reduced egg production caused by severing the DV on day 8 postemergence does not occur if the nerves connecting the CA to the brain are severed on day 1 post emergence.   However, egg production is reduced if the DV is severed on day 1 post emergence and the connections between the brain and the CA severed on day 8, suggesting that inhibition of the CA caused by severance of the DV requires innervation from the brain.   An isolated CA implanted into an animal decapitated immediately after feeding escapes from the inhibition imposed by severance of the DV.   Conversely, the CA in an insect, the head of which has been decapitated just anterior to the CA, remains inhibited. This result suggests that the head posterior to the brain must be present to maintain inhibition.   It is concluded that DV severance acts on the brain via some humoral influence to impose inhibition on the CA, and that an endocrine center in the head is required in order to maintain the inhibition.


R. Gary Chiang
Department of Biology, Redeemer College, Ancaster, ON, Canada
Archives of Insect Biochemistry and Physiology, 1998, Volume 39, Issue 3, Pages: 126-131

Partial localization of a brain factor inhibiting egg production in the blood-feeding insect, Rhodnius prolixus.

A previous study by Davey [Can J Zool 4:243-249 (1987)] showed that egg production in the blood-feeding insect Rhodnius prolixus is greatly enhanced when the corpus allatum (CA) is denervated.   This result supported findings of others that the brain of Rhodnius imposes an inhibition on the CA via its connections to the CA.   The present study identifies the nervus corporis cardiacum II (NCCII) as the nerve responsible for this inhibitory influence.   Transecting the NCCII before feeding causes a dramatic increase in the number of eggs made.   Since the NCCII is a relatively small nerve that may contain only axons of lateral and posterior neurosecretory cells in the protocerebrum, this result suggests that one or both of these cell types produce the brain factor inhibiting egg production in this insect.


R. Gary Chiang
Department of Biology, Redeemer College, Ancaster, ON, Canada
Archives of Insect Biochemistry and Physiology, 2000, Volume 44, Issue 1, Pages: 1-6

Neural inhibition of the corpus allatum in the last larval instar differs from that in adults in the blood-feeding insect, Rhodnius prolixus.

An active corpus allatum (CA) in the blood feeding insect, Rhodnius prolixus, releases a substance that inhibits metamorphosis in larvae, and activates egg production in adults.   In adults, transecting the nervus corporis cardiacum II's (NCCII), which are attached posteriorly to each protocerebral lobe, greatly increases egg production indicating that the adult CA is activated and receives neural inhibition from cells associated with the NCCII [Chiang, Arch. Insect. Biochem. Physiol. 39:126-131 (1998)].   In the present study, the NCCII's in fifth instar larvae were transected immediately before or after feeding to determine if these nerves normally inhibit CA activity in the last larval instar.   Approximately 20 to 25 days following ingestion of a blood meal, L5's with transected NCCII's emerged as fully-formed adults with no larval characteristics.   Examination of the brain in these recently emerged adults revealed that the NCCII's were absent.   Since fifth instar larvae with transected NCCII's emerged with no juvenile characteristics, cutting the NCCII's did not activate the CA, indicating that the mechanism for inhibition of the CA differs in the last larval instar and adult animals.