Within-host interactions of lymantria dispar (Lepidoptera: lymantriidae) nucleopolyhedrosis virus and entomophaga maimaiga (Zygomycetes: entomophthorales)

The interaction of two gypsy moth (Lymantria dispar) pathogens, a nucleopolyhedrosis virus (LdNPV) and a fungus (Entomophaga maimaiga), were studied by assessing mortality among dually inoculated hosts. When fourth and fifth instar gypsy moths were inoculated with a range of doses of LdNPV and a fixed dose of E. maimaiga on the same day, the majority of larvae died from E. maimaiga infections regardless of the dose of LdNPV. When the larvae were inoculated with E. maimaiga 10 days after LdNPV, there was an apparent increase in mortality of hosts induced by LdNPV. Among the fourth instars, the mortality due to LdNPV in the presence of E. maimaiga was significantly higher when insects were reared at 25 than at 20 degreesC. At 25 degreesC, the LD50 of LdNPV for fifth instars was twofold greater than that for fourth instars. For those larvae that died from LdNPV, the median survival time (ST50) of dually inoculated fourth and fifth instars was ca. 1 day shorter than those inoculated with LdNPV alone. The number of LdNPV occlusion bodies produced in the cadavers from the dually inoculated larvae was lower than those inoculated with LdNPV alone. Copyright 1999 Academic Press.