Larvae of the gypsy moth, Lymantria dispar, are susceptible to a variety of pathogens, including the baculovirus LdNPV. Although some factors contributing to effectiveness of this virus as a biological control agent have been well studied, pathogenesis within the host is relatively undescribed, especially the route by which virions spread from primary infections in the midgut tissue to secondary infections in other tissues. The two most likely routes of spread out of the midgut are (1) virions infect tracheolar cells servicing the midgut and spread through the tracheal system and/or (2) virions penetrate the basal lamina of the midgut cells directly into the hemolymph to infect hemocytes, which spread infection to other tissues. To test which of these routes LdNPV employs, we monitored viral pathogenesis over time in fourth instar gypsy moth larvae orally inoculated with a strain of virus genetically modified to express Lac Z in infected tissues. Results showed that both routes of viral spread are possible in gypsy moth larvae. The majority of infections progressed through the tracheal system, but in a consistent subset of insects the virus spread by another avenue, possibly through the movement of infected hemocytes. Further research may reveal the reason for this difference. Understanding how LdNPV spreads in gypsy moth larvae could ultimately suggest ways to improve the effectiveness of this virus as a biocontrol agent for gypsy moth.