Interpopulation variation in the prevalence and intensity of parasitic mite infection in the land snailArianta arbustorum

Abstract

Abstract. The parasitic mite Riccardoella limacum sucks blood in the lung of its host, the land snail Arianta arbustorum. The infection of various host populations was examined in Switzerland. In a lowland snail population, prevalence of infection did not vary among seasons. However, intensity of mite infection in dissected individuals of A. arbustorum was high in autumn, but low in winter and spring when ≤100 mite eggs were found attached to the lung epithelium. A novel, non‐invasive parasite screening method was used to estimate the number of mites on living host snails. An analysis of repeatability revealed that 92.9% of the snails were correctly classified as infected or non‐infected with this non‐invasive method. Prevalence of mite infection was examined in 997 adults of A. arbustorum from 11 natural populations distributed over an altitudinal gradient ranging 335–2360 m. No infected snails were found in 7 populations, while in the remaining 4 populations the prevalence of mite infection ranged 45.8–77.8%. Intensity of infection also differed among the 4 host populations. No geographic pattern in prevalence of infection was found. However, parasitic mites did not occur in snail populations situated at elevations of 1290 m or higher. A possible explanation for this finding could be that the host's hibernation period may be too long at high elevations for mites and their eggs to survive. At low elevations, other factors may affect the presence of R. limacum in the lung of A. arbustorum.

Experimental evidence for a new transmission route in a parasitic mite and its mucus-dependent orientation towards the host snail

“…A considerable variation in prevalence and intensity of R. limacum infection was found in wild A. arbustorum populations in Switzerland (Baur and Baur, 2005). The parasite occurred in 4 out of 11 populations examined, with a prevalence of 45 .…”

“…However, mite infection sporadically occurs in juvenile snails (Baur and Baur, 2005), suggesting other types of parasite transmission.…”

“…Mites leave the mantle cavity, move over the soft body of the snail, and switch to the new host. However, mites have also been observed in juvenile snails (Baur and Baur, 2005), suggesting other ways of parasite transmission. Individuals of R. limacum might also disperse via soil.…”

“…5 cm in diameter, 8 cm deep) on moist soil mixed with powdered limestone under a light : dark regime of 16 : 8 h and a constant temperature of 19¡1 xC. The soil was obtained from the locality Gurnigelbad where R. limacum may not occur (Baur and Baur, 2005). The beakers were cleaned 1-2 times per week and a diet of fresh lettuce was provided ad libitum.…”

“…The infection status and intensity of infection of both the infected and test snails were assessed using a non-invasive screening method (Baur and Baur, 2005). The soft body and respiratory pore of each individual were carefully examined for mites using a magnifying glass (10r).…”