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

MITE PATHOGENS IN IPM
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Zenner, 2005). It is not within the scope of this article to describe these viruses
comprehensively, as they are considered to be plant, resp. vertebrate viruses.
Several viruses are known from the honeybee (Apis mellifera), some of which
are associated with the varroa mite Varroa jacobsoni and the honeybee tracheal mite
(HBTM) Acarapis woodi (Sammataro, Gerson, & Needham 2000). These viruses
may always be present in the bee, either in a latent or in an unapparent form.
Wounds inflicted by the mites may activate the viruses in the bee. These viruses are
probably not capable to infect the varroa mite or the HBTM, but the presence of
these mites affects the incidence of virus disease in honey bees. The varroa mite may
also play a role in the transmission of Bee Kashmir Virus (KBV), although the virus
was already known from bee colonies before Apis mellifera colonies were infested
by V. destructor. The presence of the virus in the mite has been demonstrated by
several authors (e.g. Chen, Pettis, Evans, Kramer, & Feldlaufer, 2004). Virus-free
mites may become infected by coinhabiting in the same cell as virus-infected mites.
Whether transmission to honey bees occurs mechanically or biologically is a
question that has not yet been conclusively solved. Shen, Yang, Cox-Foster, and Cui
(2005) suggested that varroa mites cause suppression of the immune system of the
honey been which leads to activation of latent virus infections.
Liu (1991) found virus-like particles in a sample of HBTM that originated from
Scotland, but no such particles were found in HBTM samples from California.
Tissues of affected mites showed extensive lysis, while most cells were tightly
packed with virus-like particles. The virions are 27–30 nm in size and are arranged
in paracrystalline arrays forming hexagonal patterns. The ultrastructural morphology
of the particles indicates that we may be dealing with a picorna-like virus. Such
viruses resemble picornaviruses that are found in vertebrates. Picorna-like viruses
are also known from honeybees, but on the basis of histopathological studies it was
assumed that the virus found in HBTM is not derived from honeybees, but actually
multiplies inside the mite.
Kleespies, Radtke, and Bienefield (2000) performed a search for diseases in
varroa mites in parasitized bee colonies. They found mites with characteristic
internal black-colored changes of the gut and the fat body. On living adult bees,
3.6% of the mites showed this anomaly, in brood cells, even 8% of the juvenile
mites were affected. Disease incidence and intensity of the symptoms can be
enhanced by changes in environmental conditions, such as deficiency of bee brood,
deficiency of pollen, abnormal brood temperature and death of the host. The authors
found that longevity of black-colored mites was reduced by 43%. Cytopathological
studies showed the presence of a large number of spherical virus-like particles,
especially in the nuclei of fatbody and muscle tissue. The particles measure
approximately 27–60 nm in diameter and were very similar to the particles found by
Liu (1991) in HBTM. Per os infection experiments with extracts of fatbody tissue
derived from symptomatic mites were unsuccessful.
Ongus et al. (2004) detected virus-like particles in varroa mites that were
collected in bee hives in The Netherlands. The virions were mainly present in the
cytoplasm of mite tissue and resemble the virus-like particles found by Kleespies
et al. (2000). Immunochemical studies revealed that the virus was localized in the
abdominal part of the alimentary tract and in the gastric caeca, but not in the salivary