Reduction of Midgut Luminal pH in Gypsy Moth Larvae (Lymantria dispar L) Following Ingestion of Nuclear or Cytoplasmic Polyhedrosis Virus/Fluorescent Brightener on Natural and Artificial Diets

When larval gypsy moths (Lymantria dispar L.) ingest polyhedra of the nuclear polyhedrosis virus (LdMNPV) in combination with the fluorescent brightener, Tinopal LPW, midgut luminal pH drops from the normal alkaline range (ca. 10.0-10.5) to values near neutrality, and larval feeding stops. Once manifested, these effects appear to be irreversible and high larval mortality results. In the current study, we determined dose-dependent effects of LdMNPV/Tinopal ingestion on gut appearance, midgut luminal pH, and larval weight in gypsy moths reared on artificial diet. We also investigated the effect of host plant on the LdMNPV/Tinopal system, by rearing larvae exclusively on red oak foliage that had been treated with Tinopal and varying concentrations of LdMNPV. We found that treatment-associated changes in gut appearance and midgut luminal pH were similar to those observed in larvae reared on artificial diet, and larval survivorship curves were dose-dependent. In separate experiments, gypsy moth larvae were fed diet treated with cytoplasmic polyhedrosis virus (LdCPV), which undergoes early replication in midgut epithelial cells. Larval infection, as diagnosed by a change in gut tissue color from the normal tan to white, occurred concomitantly with a significant reduction in midgut luminal pH, and this phenomenon was advanced in larvae fed LdCPV/Tinopal vs. LdCPV alone.