Interactions between aNosemasp. (Microspora: Nosematidae) and Nuclear Polyhedrosis Virus Infecting the Gypsy Moth,Lymantria dispar(Lepidoptera: Lymantriidae)

Simultaneous and sequentialper osinoculations of gypsy moth larvae with theLymantria disparnuclear polyhedrosis virus (LdNPV) and aNosemasp. from Portugal demonstrated that the interaction of two pathogens during coinfection was variable, ranging from synergistic to antagonistic. Susceptibility of gypsy moth larvae to viral infection was unaffected by simultaneous and subsequent microsporidian infection. This resulted from the comparatively slow pathogenesis of the microsporidium when compared to the virus. Viral infectivity, however, increased 10-fold when larvae were preinfected withNosemasp.per os,or through transovarial infection. Time to death decreased for larvae infected with both pathogens compared to larvae infected with the virus alone. Polyhedron production was significantly reduced by microsporidian infection preceding viral infection. In this infection sequence, larvae died at an earlier stage and were less than half the mass of cadavers infected with virus alone. The biological significance of these results on gypsy moth population dynamics and the implication for use of thisNosemasp. from Portugal in gypsy moth biological control are discussed in the context of viral epizootiology.