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AmoebasNearly all entomogenous amoeba species are in the families Amoebidae (Malameba, Malpighamoeba, Malpigiella; strictly entomogenous genera), and Endamoebidae, found in roaches and various flies and fleas, as well as in other animals (Brooks, 1988). Most insect-associated amoeba species are commensuals in digestive tracts of their hosts, but some are pathogens producing amoebiasis (or amoeboses) (Tanada and Kaya, 1993). Amoebas have a simple life cycle; there are no special stages with the exception of a cyst form in some species, and reproduction is by simple binary or multiple fission. The two most studied species, Malpighamoeba mellificae and Malameba locustae, both in the family Amoebidae, pack the Malpighian tubules, destroying the epithelia and producing chronic but debilitating effects (Tanada and Kaya, 1993). M. mellificae, producing spring disease of honey bees, often occurs in mixed infections with Nosema apis, a microsporidium. Mixed infections are more severe than M. mellificae infections alone. M. mellificae infects only adult bees and is transmitted orally by ingestion of the cyst stage. The disease is usually chronic but Malpighian tubule epithelia can be destroyed and the lumens blocked by the pathogen, which may result in death of the bees. Infections are typically seen in the spring, far less occur in the summer. The cure is sanitation, cleaning and disinfecting hives, and a clean water supply (Bailey, 1963). Malameba locustae (Family Amoebidae) is a pathogen of approximately 50 species of grasshoppers and locusts. Prevalences in the field are usually low (Brooks, 1988), but this pathogen can devastate laboratory colonies. M. locustae primarily occurs in the lumens of Malpighian tubules, which can swell enormously (Taylor and King, 1937). The pathogen is transmitted by ingestion of cysts on food and by cannibalism of infected hosts. Severe chronic effects result from infection including reduced adult longevity and fecundity, reduced activity, loss of appetite and death (Taylor and King, 1937). Biological Control: Amoebic diseases have been more of a problem in beneficial insects and insect colonies than useful as biological control agents. Some studies have been conducted and suggestions have been made regarding utilization of M. locustae as a control agent in range grasshoppers (Lange and Wittenstein, 1998). |
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