An investigation into the life-histories and ecology of the Hydracarina.

The work described in this thesis was designed to throw some light on the problems of the larval behaviour and way of life of the British Hydracarina. Although these animals are a common and numerous element in nearly all fresh-water habitats the full life-histories are known for very few. The principal method of investigation used in this work was by catching and examining aquatic invertebrates and attempting to identify any mite larvae which they were carrying. The lack of any complete key made it necessary to attempt to breed these larvae through to the adult stage and this was done successfully in five cases. The hosts for a further three species were found by using larvae bred in the laboratory to produce parasitic infections of hosts under experimental conditions, while another seven species of larva were identified on the host from Sparing's key and by comparison with bred specimens. The actual transfer of the larvae onto their hosts was observed for an Arrenurus species, parasitic on Zygopteran adults, and for Protzia eximia, Protz, whose larvae jump distances of up to 2 cm. from the water or land surface to reach their positions on their Empid or Trichopteran hosts. The larvae of two Unionicola spp, believed since the time of Bonz, 1783 to be free-living, were shown to be parasitic on Chironomids, thus making the position of the Unionicolidae in the Super-family Pionae much more comprehensible than it had hitherto appeared. Collections of large numbers of Chironomids showed the great importance of this group in the life cycles of the Hydracarina, and it also became obvious that the Nematocera in general appear to be by far the most important host group for the water-mites. In the appendix are descriptions of three previously unknown larvae together with a table summarising present knowledge of the hosts of water-mites.