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FlagellatesFlagellates are characterized by adult morphology, body forms based on shape and the location from which the flagellum emerges from the kinetoplast- a DNA rich organelle. Life cycles are varied and different stages usually have different body forms, including cysts. Sexual reproduction occurs but appears to be rare; most flagellates undergo simple binary fission (Tanada and Kaya, 1993). Approximately 400 species of flagellates have been associated with insects, but only a few are pathogenic (Lipa, 1963). The majority are commensals or are vectored by the insects to hosts in other taxa. About 350 insect species have been found to host monoxenous, or one host, species of flagellates (Wallace, 1966). Higher trypanosomatids (the vectored species) are heteroxenous, having more than one host. Most entomogenous flagellates are in the family Trypanosomatidae. They have not been well studied, and there is limited knowledge about pathogenesis and transmission between hosts. The disease, flagellatoses or flagelloses, is primarily localized in the host digestive tract of the host, where some flagellates may form a carpet-like layer attached to the intestinal wall using their flagella to weave into the microvilli (Wallace, 1979). Other species may be free in the lumen. Some species, however, may enter the hemocoel, salivary glands or Malpighian tubules and these are typically more virulent, even fatal. Most described species of trypanosomes occur in Hemiptera (35%) and Diptera (55%) (Wallace, 1966), and a few occur in Siphonaptera. In the laboratory, flagellates exhibit little host specificity. One species has been found infecting 26 species of flies in different families in the field (Wallace, 1966), although current molecular techniques could possibly differentiate some of these isolates. Transmission between hosts is usually by ingestion of feces, blood, plant sap, cadavers, or by cannibalism. Infections in some species can persist through larval stages into the adult stage of the host. The best known trypanosomatid flagellates are not insect pathogens but those vectored by insects to vertebrate animals. Some of these species do reproduce in the insect vector, and a few may also be pathogenic to the vector. A huge literature is available for study of insect vectored flagellates. Biological Control: Because of the weak pathology of flagellate diseases in insects, there is little interest in their use as biological control agents. Most interest in this group is focused on the role of hosts as vectors of vertebrate pathogens. |
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