REDUCTION OF MIDGUT LUMINAL PH IN GYPSY-MOTH LARVAE (LYMANTRIA-DISPARL) 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 fluorescen t brightener, Tinopal LPW, midgut luminal pH drops from the normal alk aline range (ca. 10.0-10.5) to values near neutrality, and larval feed ing stops. Once manifested, these effects appear to be irreversible an d high larval mortality results. In the current study, we determined d ose-dependent effects of LdMNPV/Tinopal ingestion on gut appearance, m idgut luminal pH, and larval weight in gypsy moths reared on artificia l diet. We also investigated the effect of host plant on the LdMNPV/Ti nopal system, by rearing larvae exclusively on red oak foliage that ha d been treated with Tinopal and varying concentrations of LdMNPV. We f ound that treatment-associated changes in gut appearance and midgut lu minal 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 midg ut epithelial cells. Larval infection, as diagnosed by a change in gut tissue color from the normal tan to white, occurred concomitantly wit h a significant reduction in midgut luminal pH, and this phenomenon wa s advanced in larvae fed LdCPV/Tinopal vs. LdCPV alone. (C) 1994 Acade mic Press, Inc.