The spiracle of Ixodes ricinus (L.) (Ixodidae: Metastigmata: Acarina): a passive diffusion barrier for water vapour

Abstract

The strurturc or the spiracle in the adult female of Ixodrs ricinus (L.) is assessed. Gaseous exchange between the tracheal system and the external atmosphere is shown to occur only via the aeropyles in the surface of the sieve plate and is regulated by the atrial valve. The elaborate structure is shown to be an effective passive mechanism to retard the transpiration of water vapour from the tracheal system. The prdicels reduce airflow within the labyrinth to a minimum, while the size and arrangement of the iieropyles allow thr formation of a cloud of water vapour above the surface of the spiracle. It is from this cloud which diffusion of water vapour takes place, with no significant rhanges in water vapour pressure occurring within the tracheal system or the spiracle itsel[ 'I'he mechanics of the system are analysed.

The spiracle glands in Ixodes ricinus (Linnaeus, 1758) (Acari: Ixodidae)

“…The gross morphology is in agreement with available descriptions of this and other ixodid species (Pugh et al, 1988;Pugh, 1997): the connection between the labyrinth, the sub-ostial space and the tracheal atrium is clearly visible. Moreover, we confirmed connections between the chambers by fenestrations, the closed condition of the "ostium" (Hinton, 1967; Pugh, 1997;Woolley, 1972) and the cuticular channels through the baseplate.…”

“…Different kinds of chambers are distinguished in the labyrinth of Ixodidae. One of them, the primary atrial chamber, is connected by a pore to the body surface and via a cuticular duct to the hypodermis (Pugh et al, 1988;Pugh, 1997).…”

The respiratory system of the femaleVarroa jacobsoni (Oudemans): its adaptations to a range of environmental conditions

“…The micropapillae are more likely impede transpiration of water vapour from the tracheal system, thus allowing the establishment of diffusion gradients and barriers, a function ascribed to similar structures (pedicels) in the spiracular plates of ixodid ticks (Pugh et al, 1988 ).…”

Morphology of spiracles in adult Hyalomma truncatum ticks (Acari; Ixodidae)

“…The spiracles of ticks are part of the respiratory system which regulate the exchange of oxygen and waste gases and restrict water losses from the tracheal lumen into the subsaturated atmosphere of the environment (Hefnawy, 1970;Rudolph and Kniille, 1979;Kniille and Rudolph, 1982;Needham and Teel, 1986;Pugh et al, 1988Pugh et al, , 1990Sonenshine, 1991;Fielden et al, 1994). However, with regard to the modus operandi of the respiratory gas exchange and the control of tracheal water loss, the functional morphology of the spiracle of ixodid ticks has so far been deduced mainly from light microscopical or histological investigations considering only a few species of the genera lxodes (Batelli, 1891;Norden-ski61d, 1906;Bonnet, 1907;Schulze, 1923;Falke, 1931;Arthur, 1956;Babos, 1964), Haernaphysalis (Nuttall et al, 1908;Roshdy and Hefnawy, 1973;Roshdy, 1974;Sixl and Sixl-Voigt, 1974) and Dermacentor (Bishopp and Wood, 1913;Arthur, 1960;Babos, 1964).…”

“…However, with regard to the modus operandi of the respiratory gas exchange and the control of tracheal water loss, the functional morphology of the spiracle of ixodid ticks has so far been deduced mainly from light microscopical or histological investigations considering only a few species of the genera lxodes (Batelli, 1891;Norden-ski61d, 1906;Bonnet, 1907;Schulze, 1923;Falke, 1931;Arthur, 1956;Babos, 1964), Haernaphysalis (Nuttall et al, 1908;Roshdy and Hefnawy, 1973;Roshdy, 1974;Sixl and Sixl-Voigt, 1974) and Dermacentor (Bishopp and Wood, 1913;Arthur, 1960;Babos, 1964). Scanning electron microscopical (SEM) studies included species of the genera Ixodes (Sixl et al, 1971;Woolley, 1972;Sixl and Sixl-Voigt, 1974;Pugh et al, 1988), Aponomma (Pugh et al, 1990), Dermacentor (Sixl et al, 1971;Woolley, 1972;Pugh et al, 1990), Rhipicephalus (Pugh et al, 1990), Boophilus (Hinton, 1967;Roshdy and Hefnawy, 1973;Roshdy, 1974), Haemaphysalis (Sixl et al, 1971;Woolley, 1972;Roshdy and Hefnawy, 1973;Roshdy, 1974;Sixl and Sixl-Voigt, 1974) and Arnb~yomma (Woolley, 1972;Rudolph and Kniille, 1979), but were almost exclusively confined to the depiction of the surface profile of the spiracular plate (Hinton, 1967;Roshdy and Hefnawy, 1973;Roshdy, 1974) or, additionally, to its structural organization …”