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First published online January 16, 2009
Journal of Experimental Biology 212, 378-386 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.024109
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Neuroendocrine control of ionic homeostasis in blood-sucking insects

Geoffrey M. Coast

Birkbeck College, School of Biological and Chemical Sciences, Malet Street, London, WC1E 7HX UK


Figure 1
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  		Fig. 1. An overview of osmotic and ionic concentrations and fluid movements during rapid diuresis in a fifth-instar Rhodnius nymph. Coloured arrows, used to indicate transport across the anterior midgut and across upper and lower Malpighian tubule segments, correspond to those used for the dose–response curves in Fig. 4. Ion concentrations are given in mmol l–1. Based upon data from Maddrell (Maddrell, 1976Go).

 

Figure 2
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  		Fig. 2. Hypothetical dose–response curves for a diuretic hormone that stimulates fluid absorption from the anterior midgut (red curve) and fluid secretion by upper Malpighian tubules (blue curve). The vertical lines show how the diuretic hormone concentration will respond to an increase (a) or decrease (b) in haemolymph volume. Changes in diuretic hormone concentration have no effect on fluid secretion, which is already maximal, but will decrease (a) or increase (b) fluid absorption so as to restore haemolymph volume until the two rates are equal (arrow). Redrawn from Maddrell (Maddrell, 1980Go).

 

Figure 3
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  		Fig. 3. A schematic diagram of the posterior region of the MTGM showing the localisation of neurosecretory cells containing factors that are known to influence tubule secretion. Serotonin- and Rhopr-DH31-immunoreactive material is present in DUM neurons and axons (blue) that exit via abdominal nerves (AN) 1–5. Kinin- and CRF-like DH-immunoreactive material is present in groups of posterior lateral neurosecretory cells and axons (green) exiting via AN1 and AN2. Rhopr-CAP2b-immunoreactive material is present in three pairs of ventral medial neurosecretory cells and axons (red) exiting via AN2–AN4. Based upon data from Orchard et al. (Orchard et al., 1989), Te Brugge et al. (Te Brugge et al., 2001Go; Te Brugge et al., 2005Go) and Paluzzi and Orchard (Paluzzi and Orchard, 2006Go).

 

Figure 4
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  		Fig. 4. Normalised dose–response curves for the effects of serotonin in stimulating fluid absorption from the anterior midgut (red curve), fluid secretion by upper Malpighian tubules (blue curve) and K+ uptake from lower Malpighian tubules (green curve). Vertical lines indicate serotonin concentrations in haemolymph of unfed fifth-instar Rhodnius nymphs (0), and at 5 and 60 min after the onset of feeding. Based upon data from Maddrell et al. (Maddrell et al., 1971Go; Maddrell et al., 1993), Farmer et al. (Farmer et al., 1981Go) and Lange et al. (Lange et al., 1989Go).

 

Figure 5
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  		Fig. 5. (A) The rate at which urine droplets are voided during the pre-diuresis and subsequent diuresis of An. gambiae fed on a human volunteer. During peak diuresis, urine drops are voided at >1 min–1 but are voided less regularly during late diuresis. (B) The percentage of imbibed plasma water (blue bars), Na+ (red bars) and K+ (green bars) excreted during pre-diuresis, and the peak and late phases of diuresis by the same mosquito as in (A) (G.M.C., unpublished observations).

 

Figure 6
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  		Fig. 6. Water loss from female An. gambiae fed on blood (A) and injected with 1 µl of 0.9% NaCl (B). Water loss was recorded using a flow-through humidity meter. The initial peak in the recordings represents water vapour entering the chamber at the start of the experiment, whereas subsequent

 

Figure 7
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  		peaks correspond to the expulsion of drops of urine from the anus (G.M.C., unpublished observations).

 

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© The Company of Biologists Ltd 2009