Host-Parasite Interaction and Impact of Larval Water Mites on Insects

Abstract

The water mites or Hydrachnidia ( = Hydrachnellae, = Hydracarina) represent an extremely successful lineage of the order Acariformes (subclass Acari) that is secondarily adapted to an aquatic existence. Worldwide, more than 300 genera in 45 families and seven superfamilies contain over 3000 described species (24). These organisms show a wide variety of adaptations to the aquatic environment. Water mites are found in almost every freshwater habitat and frequently occur in densities exceeding 200 per square meter. The basic acariform life cycle consists of egg, inactive prelarva, larva, protonymph, deutonymph, tritonymph, and adult. In the Parasitengona, which includes the Hydrachnidia, the protonymph and tritonymph are quies­ cent and occur within the cuticle of the previous stages, the nymphochrysalis and teleiochrysalis, respectively. While the deutonymph and adult instars are typically free-living predators and are very similar in appearance, the larval stage is morphologically distinct and parasitic. Almost all species of water mites that are parasitic as larvae use insects as hosts. Secondary loss of the parasitic association has occurred among isolated species of Hydrachnidia; sometimes an active larval stage is bypassed entirely, with the deutonymph emerging from the egg (49, 64, 77). Adults and deutonymphs of some mites such as Najadicola ingens and some species of Unionicola are parasites (49, 64). However, I limit my discussion to larval-stage parasites of insects. Understanding of the parasitic relationship between water mites and insects has been greatly hampered by the difficulty of associating adult mites with the