Host-pathogen relationships of two previously undescribed microsporidia from the Indian-meal moth, Plodia interpunctella (Hübner), (Lepidoptera: Phycitidae)

Abstract

Moribund larvae of the Indian-meal moth, Plodia interpunctella (Hübner), collected in California harbored dual infections of two previously undescribed species of Microsporidia, Nosema heterosporum sp. n. and Thelohania nana sp. n. N. heterosporum is highly infective and was readily transmitted perorally to larvae in laboratory tests; such infections were usually progressive. Transovarian transmission did not occur. Midgut epithelium and fat tissue are primarily invaded; silk and salivary glands and muscle are invaded to a relatively light degree. Spores are morphologically variable and may remain viable for at least a year at 4°C in aqueous suspension. T. nana primarily invades fat tissue and occasionally occurs in muscle. It was readily transmitted to young larvae, but it has only been observed in dual infections. The thelohanian may occur independently in isolated fat lobes adjacent to tissue harboring Nosema. Both microsporidians were transmitted to the navel orangeworm, Paramyelois transitella (Walker), and the greater wax moth, Galleria mellonella (Linneaus). The almond moth, Cadra cautella Walker, the raisin moth, Cadra figulilella Gregson, the tobacco moth, Ephestia elutella (Hübner), the confused flour beetle, Tribolium confusum Jacquelin duVal, and the dried fruit beetle, Carpophilus hemipterus (Linnaeus), were not susceptible in laboratory tests.