Morphology and development of Vairimorpha spec. (Microsporida, Nosematidae) from diamondback moth Plutella xylostella (Lep., Yponomeutidae)

The morphology and development of Vairimorpha spec. are described from chro nically infected Plutella xylostella. We detected a temperature independent dimorphism of Vairimorpha spec. in P. xylostella by rearing at 20-23 degre es C. All organs in each developing host stage of P. xylostella were infect ed heavily, especially in haemocytes and fat bodies. After infection of the host a complicated development cycle starts, which is characterized by mer ogony and sporogony. A disporoblastic (Nosema type) and an octosoproblastic (Thelohania type) life cycle was found to be temperature independent. Mero nts, which are spherical with two or four nuclei in diplokaryotic arrangeme nt, precede both types of sporogony. Both types occur mainly in the fat bod ies of the larvae and adults, shown after staining with Giemsa and Iron hae matoxylin.