CHAPTER EIGHT 



TEMPERATURE -DEPENDENT SPORE DIMORPHISM 

 IN BURENELLA DIMORPHA 



The effect of temperature on the relative abundance 

 of MB and NMB spores was first studied by Maddox (1966) 

 in the dimorphic microsporidium Vairimorpha necatrix (Kramer) . 

 This parasite was originally thought to be a mixed infection 

 involving two species of microsporidia, Nosema necatrix Kramer 

 and Thelohania diazoma Kramer, that produced NMB and MB 

 spores, respectively, in lepidopteran hosts (Kramer, 1965). 

 Maddox demonstrated that only NMB spores are produced if 

 infected armyworm larvae , Pseudaletia unipuncta (Haworth) , 

 are reared at temperatures of 32° C or above. At lower 

 temperatures (16° C) 40Z or more of the spores are the MB 

 type. Maddox infected armyworm larvae with an apparently 

 pure suspension of NMB spores obtained from larvae reared 

 at elevated temperature, and found that both types of spores 

 were produced in larvae held at temperatures below 32° C. 

 This led Maddox to suggest (as the more radical of two pos- 

 sibilities) that N. nectarix and T. diazoma were " . . .not 

 two species at all, but rather one species with two distinct 

 developmental cycles and resulting spore forms, the ratio 

 of which is influenced by temperature" (p. 112). 



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