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

Adoxophyes honmai larvae inoculated with 10x 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. (C) 2004 Elsevier B.V. All rights reserved.