Larvae of the fresh-water mite Limnochares aquatica (L., 1758) (Acariformes: Hydrachnidia: Limnocharidae) and their stylostome evolving during feeding on Gerris lacustris (L., 1758) (Hemiptera: Gerridae)

Abstract

The larvae of the fresh-water mite Limnochares aquatica (L., 1758) feeding on the pond-skaters Gerris lacustris (L. 1758) and their stylostome were studied using laboratory observations, light-microscope, SEM and TEM methods. The emergence of unfed larvae from the eggshell in the laboratory was also traced. Larvae possess a lamellar area on the ventral surface of the hypostome (supposed sucker or velum), which adheres to the host cuticle during feeding. The bifurcated palpal claws do not pierce the host cuticle and remain outside it during the larval feeding. The larvae secrete at least two saliva portions – the initial one gradually penetrating the host cuticle to which the cheliceral movable digits firmly adhere, and the main one forming the stylostome as such situated underneath the host cuticle. The developed stylostome does not immerse deep into the body cavity and is represented by associations of the uniformly electron-dense globules, the largest of which are pierced by the axial canal. This type of stylostome may be conventionally identified as unclearly ramified structured totally composed of the saliva secretion. The host tissue is partly destructed by the parasite saliva action, and the host defence reaction is imperceptible. The observed stylostome structure may be considered as an initial form for the fresh-water mite branch of the Parasitengona.