Variety and diversity of microsporidia isolated from the common cutworm Spodoptera litura in Chichijima, Ogasawara Islands

Abstract

The efficacy of biological control agents has recently been attracting attention because it is now thought to be possible to protect plants from insect pests with minimal effects on the environment. However, many microbial control agents may also affect beneficial insects, such as silkworms and honey bees. For agents to be practical, it is necessary for them not to have an effect on beneficial insects. Microsporidia are obligate parasitic protozoa. Approximately 1,300-1,500 species belonging to 187 genera have been isolated (Vávra and Lukeš, 2013), and most of them infect a variety of insects. It is anticipated that they will be utilized as microbial control agents with selective effects against insect pests because of their host specificity. However, many microsporidia species that infect insect pests of Lepidoptera also infect beneficial insects, such as silkworms. Nosema bombycis is a highly virulent microorganism causing pébrine disease in the silkworm, Bombyx mori, and damage due to this disease has recently been reported worldwide (Hukuhara, 2011). To utilize microsporidia for the control of insect pests, it is necessary to select more host-specific strains with no influence on silkworms. To determine the actual conditions of microsporidian infection in a field population of lepidopteran insects, we conducted a study to isolate and analyze entomopathogenic microsporidia from the common cutworm Spodoptera litura in Chichijima, Ogasawara islands. Chichijima has not been previously explored for microsporidia. We periodically collected male moths of the lepidopteran insect pest S. litura using sex pheromone traps. After detecting microsporidian spores from S. litura moths, we attempted to group the microsporidian strains by spore size comparison and phylogenetic analysis using small-subunit ribosomal RNA (SSU rRNA) sequencing.