An entomopoxvirus and a granulovirus use different mechanisms to prevent pupation of Adoxophyes honmai

Adoxophyes honmai larvae inoculated with 10× the 95% lethal concentration of an entomopoxvirus (AdhoEPV) did not pupate, underwent a prolonged larval stage, and died during their final instar, unlike non-infected larvae which pupated after five larval instars. In previous work we showed that a granulovirus (AdhoGV) also retarded host development and prevented pupation of A. honmai larvae. In this study, endocrinological alterations in AdhoEPV-infected larvae were compared to those in AdhoGV-infected larvae. AdhoEPV-infected larvae had no peak of juvenile hormone (JH) esterase activity during the final instar, suggesting that JH titers in virus-infected larvae remained high during this period. In AdhoEPV-infected larvae the ecdysteroid titer remained low during the final instar, whereas in AdhoGV-infected larvae it peaked during the final instar and remained high towards the later stages of this instar. Ecdysteroid UDP-glucosyltransferase (EGT) activity was detected in the hemolymph of AdhoGV-infected A. honmai larvae, suggesting that the ecdysteroid would be inactivated in these insects. No EGT activity was detected in the hemolymph of either AdhoEPV-infected or non-infected A. honmai larvae. Thus, while AdhoEPV and AdhoGV both prevent pupation of A. honmai larvae, the mechanisms by which they do so appear to be different.