One of several barriers to the effective use of the baculovirus Lymantria dispar nucleopolyhedrovirus (LdNPV) to control gypsy moth (Lymantria dispar) is susceptibility to viral infection varies within an instar. A viral LD80 for newly molted larvae will only kill about 40% of larvae infected at 48-72 hours post-molt, a phenomenon called intrastadial developmental resistance. Our hypothesis is that this pattern is driven by differences in the ability to mount anti-viral defenses. To begin exploring the basis of this resistance, we examined differences in hemocyte numbers, composition, and behavior between susceptible and resistant aged gypsy moth larvae, both with and without baculovirus infection. We assessed total hemocyte numbers and composition from hemolymph samples collected at different times post-inoculation. Hemocyte behavior was observed by making time-lapse movies of hemocytes. The comparison of susceptible and resistant aged larvae and uninfected and infected larvae yielded interesting results, particular in regards to one hemocyte type, the oenocytoid, which is thought to be involved in several important insect immune processes. There were also differences in the level of immunological activity of hemocytes in different treatments.