Two New Species of Nosema (Microsporida: Nosematidae) from the Mexican Bean Beetle Epilachna varivestis (Coleoptera: Coccinellidae)1,2

Two new species of the genus Nosema (Microsporida: Nosematidae) are described from the Mexican bean beetle, Epilachna varivestis (Coleoptera: Coccinellidae) and their life cycle stages studied by light and electron microscopy. Both species are monomorphic and disporous: they develop in direct contact with the cytoplasm of host cells and the nuclei of all stages are diplokaryotic. The more virulent species produces systemic infections most extensively in the adipose tissue, muscles, and Malpighian tubules of larvae and also invades the reproductive tissues of adult beetles. During merogonic development, it forms chains of diplokaryotic meronts. The fine structure of the sporoblast nuclei shows clumped material in the pole of each nucleus opposite their common plane of apposition. Spores are straight to slightly curved and ovocylindrical in shape and they measure 5.3 ± 0.13 × 2.1 ± 0.03 μm. The less virulent species also invades most host tissues but does not develop in the midgut epithelium; the Malpighian tubules are the principal site of its development and it also invades the ovaries and testes of adult beetles. Merogony occurs exclusively as the result of binary fission of diplokaryotic meronts. The plasmalemma of the meronts is covered with a thin deposit of exospore material upon which are located closely packed tubules that encircle the body transversely. A thickened deposit of exospore material on the surface of the diplokaryotic sporonts later obscures these tubules. Other tubules occur free in the host cell cytoplasm or attached to the plasmalemma of meronts and sporonts. Secretory granules also occur free or in chains in the host cytoplasm and are probably produced from the surface of the sporoblasts. Sporoblasts also contain an unusual cup-shaped organelle associated with a dense body, which is apparently involved in the formation of the polar tube and its associated organelles in the anterior part of the spore. Spores are ellipsoidal to slightly pyriform and measure 4.7 ± 0.06 × 2.6 ± 0.03 μm.