A survey of microbial, insect and nematode parasites of Tipulidae (Diptera) larvae in north-east England.
Abstract
The parasites of larvae of species of Tipula larvae were surveyed, principally at four locations between September 1973 and July 1974. The most common host species was T. paludosa Mg. Some new parasites were recorded together with previously-recorded parasites in new hosts. It is concluded that the parasites were not a highly significant cause of larval mortality. The most common parasites were gregarines and coccidia, but there was little evidence to suggest that they affected the well-being of their hosts. There were significant differences in the percentages of larvae infected with protozoa between host species, between locations and between areas at the same location. Some possible reasons for these differences are discussed. Oxyuroid nematodes also had little apparent effect on their hosts. Larvae parasitised by Tipula iridescent virus, Tipula nuclear polyhedrosis virus, bacteria, fungi, microsporidia, mermithids, tachinids or phorids were rarely found. The viruses, merithids and tachinids usually killed their hosts and are therefore potential biological control agents. The other parasites require further evaluation to determine their effect on the host. For any parasite to be a successful biological control agent it would be necessary to induce infections when the tipulid larvae are in the earlier instars, and in larger proportions of the populations than it normally occurs under natural conditions.<new para>ADDITIONAL ABSTRACT:<new para>From 1.0 to 12% of tipulid 3rd- and 4th-instar larvae from various locations in Northumberland, England, were found infected with mermithids. The number of mermithids/host varied from one to 33. Most of the hosts were Tipula paludosa but one T. marmorata (? alpium) and one Ptychoptera sp. were also infected. Many 4th-instar T. paludosa, T. luna and T. unca contained Thelastomatidae generally in the hind-gut, but occasionally in the mid-gut. Both the number of nematodes/host and their size (up to 4 mm long) were highly variable. The nematodes were thought to be of the genus Cephalobellus and T. luna and T. unca are considered new hosts. Effects of the parasites on the hosts, host defence mechanisms and possible factors controlling the prevalence of parasites are discussed. The mermithids usually killed their hosts and their potential as biological control agents is briefly mentioned.<new para>ADDITIONAL ABSTRACT:<new para>Large numbers of tipulid larvae examined from various locations in Northumberland, England, were found infected with protozoa. Gregarines intermediate in morphology between Gregarina longa and Hirmocystis ventricosa, and also near-spherical types were found, and were grouped as Gregarina spp. These were the most common parasites found, being in the intestines of most larvae examined immediately after collection. Some of the gregarines are previously unrecorded (one type, found in half the 8 Tipula variipennis larvae examined was sometimes over 2 mm long). New hosts are recorded for Gregarina spp., Actinocephalus tipulae, haemocoelic gregarines and coccidia. A new microsporidian was found in the nerve tissue of 3 T. paludosa larvae. Variation in protozoan infections, possible factors controlling the prevalence of parasites, effects of parasites on their hosts and host defence mechanisms are discussed. There was little evidence to suggest that the gregarines and coccidia affected the well-being of their hosts.