Ecological vs physiological host specificity: the case of the microsporidium Nosema pyrausta (Paillot) Weiser, 1961

The microsporidium Nosema pyrausta (Paillot) Weiser, 1961 plays an important role in the mortality of the European corn borer Ostrinia nubilalis (Hübner, 1796), and shows high virulence to the beet webworm Loxostege sticticalis (Linnaeus, 1761). In contrast, the greater wax moth Galleria mellonella (Linnaeus, 1758) and the gypsy moth Lymantria dispar (Linnaeus, 1758) are referred to as resistant hosts, slightly susceptible to this microparasite. The goal of the present study was to test N. pyrausta against a broad range of lepidopteran species with different taxonomy, physiology, and ecology. The susceptibility to N. pyrausta spores fluctuated greatly among members of various families and superfamilies of Lepidoptera. As many as 13 species tested were found to be refractory (not able to support the development of the microsporidium), including three species of Yponomeutoidea, four species of Papilionoidea, one species of Pyraloidea, two species of Bombycoidea, and three species of Noctuoidea. The species found to be susceptible (with a high proportion of specimens displaying developed infection) included: Evergestis forficalis (Linnaeus, 1758) (Crambidae), Aglais urticae (Linnaeus, 1758) (Nymphalidae), and Dendrolimus sibiricus Chetverikov, 1908 (Lasiocampidae). The species newly found to be highly susceptible (high proportion of infected insects accompanied with high levels of early mortality) were: Spodoptera exigua (Hübner, 1808) (Noctuidae) and Aglais io (Linnaeus, 1758). Large quantities of spores can be produced in vivo using substitute laboratory host A. urticae. These results confirm previous observations that physiological host range of microsporidia (observed under experimental conditions) is broader than the ecological one (observed in nature).