[Edited_by_A._Ciancio,_C.N.R.,_Bari,_Italy_and_K.(Bookos.org)

MITE PATHOGENS IN IPM
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Coccidia differ from the gregarines in their gamogony: female gamonts of
gregarines give rise to a number of gamonts whereas those of Coccidea only to
single gamonts. One coccidian species has been described from an oribatid (Purrini,
1984).
5.2. Microspora Infections in Mites
Microspora (or Microsporidia) are obligate intracellular parasites with a broad host
range including all animal groups. They rank among the smallest eukaryotes (1–40 μm)
with the shortest eukaryotic genome and are generally considered to be a separate
phylum within the subkingdom Protozoa. However, recent molecular studies
indicate that they may be considered to be extremely reduced fungi. Replication
takes place within the host's cells, which are infected by means of unicellular spores.
Microsporidia are unusual in lacking mitochondria and in having mitosomes. 4
They also lack motile structures such as flagella. The spores are protected by a
layered wall made of proteins and chitin. Their interior is dominated by a unique
coiled structure called the polar filament. Spores, the infective stage, are ingested by
the host and, in the midgut, their polar filament is instantaneously emitted as turning
a garden hose inside out. The polar tube penetrates the host cell and the contents of
the spore are pumped through it without destruction of the host cell. Within the host
cell, an increase in numbers followed by the development into new spores takes
place. In this way, the infection spreads throughout the host. Many different tissues
may be affected. The spores may be released into the environment during the life of
the host or after its death. The spores are the only stages that can survive outside the
host. Many microsporidia have very complex life cycles with several spore types
and host involved. Microsporidiosis is often transmitted vertically (from mother to
offspring), usually without spores as intermediary. Vertical transmission may be
transovarial, by passage though the ovary, or transovum, a form of transovarial
transmission in which the pathogen enters the egg while it is still in the ovary.
Taxonomy was in the past mainly based on spore size and shape. These
characters are, however, unsatisfactory and for that reason, ultrastructural
characteristics have been used. This has caused a considerable revision in this group
of pathogenic organisms (Sprague, Becnel, & Hazard, 1992). Recently, several
research groups have started to integrate molecular techniques for phylogenetic
studies of Microsporidia. This will undoubtedly result in a new revision of these
taxa.
The first microsporidium described in mites was Nosema steinhausi (Weiser,
1956) from the stored product mite Tyrophagus putrescentiae (Tyroglyphidae). The
disease affects both adults and nymphs. Experiments in a colony of the mite showed
that the disease progressed from about 10% infection at the start of the experiment to
4 A mitosome is an organelle found in some unicellular eukaryotic organisms. The
mitosome has only recently been found and named, but its function has not yet been
well characterized. It is sometimes termed a crypton.