64 



The dimorphic nature of this microsporidiiitn was experi- 

 mentally demonstrated by Fowler and Reeves (1974) through 

 the use of mechanical as well as thermal and temporal methods 

 to separate the two spore types for transmission studies. 

 They retained the name N. necatrix, suppressing the name 

 T. diazoma . Pilley (1976), recognizing that N. necatrix does 

 not conform to the definitive characteristics of the genus 

 Nosema, reassigned it to a new genus, Vairimorpha . Jouvenaz 

 and Hazard (197 8) observed that V. necatrix and B. dimorpha 

 are related and suggested that the genus Vairimorpha properly 

 belongs in the family Burenellidae. 



The temperature dependence of spore dimorphism in V. 

 necatrix was also demonstrated by Maddox and Sprenkel (1975), 

 who serially passed V. necatrix spores through eight genera- 

 tions of P. unipuncta held at 21.1° and 32° C. Maddox and 

 Sprenkel also demonstrated temperature-dependence of spore 

 dimorphism of " Nosema plodia e - Thelohania nana " Kellen and 

 Lindegren, and in an undescribed microsporidium. Maddox 

 (1966) described the V. necatrix infections of P. unipuncta 

 reared at elevated temperature as "light." 



The primary purpose of the experiments reported here 

 was to determine whether spore dimorphism in B. dimorpha 

 is temperature dependent. The effects of temperature on 

 spore yield ("light infections", Maddox) and size were also 

 measured. In addition, since the MB spores of B. dimorpha 

 develop in the fat body while NMB spores have been found 



