Genetic and biological comparisons of four nucleopolyhedrovirus isolates that are infectious to Adoxophyes honmai (Lepidoptera: Tortricidae)

The smaller tea tortrix, Adoxophyes honmai (Lepidoptera: Tortricidae), is one of the most important pests of tea plants in Japan. Adoxophyes honmai nucleopolyhedrovirus (AdhoNPV) isolates from Tsukuba (AdhoNPV-Ts) and Tokyo (AdhoNPV-To), Japan, and Adoxophyes orana nucleopolyhedrovirus (AdorNPV) isolates from England (AdorNPV-En) and the Netherlands (AdorNPV-Ne) were subjected to genetic and biological comparisons to select a candidate NPV isolate to control A. honmai. Restriction endonuclease (REN) analysis demonstrated that AdhoNPV-Ts and AdhoNPV-To had similar REN patterns, whereas AdorNPV-En and AdorNPV-Ne exhibited different REN patterns from each other as well as those of AdhoNPV-Ts and AdhoNPV-To. Bioassays with fourth-instar A. honmai larvae showed that AdorNPV-En was most pathogenic, with the lowest LD₅₀ of 37 occlusion bodies (OBs) per larva. When A. honmai neonates were inoculated with each isolate, most larvae infected with AdhoNPV-Ts and AdhoNPV-To were killed in the final (fifth)-instar, whereas larvae infected with AdorNPV-Ne were killed at every instar and larvae infected with AdorNPV-En were killed at the first- to third-instar. AdorNPV-En or AdhoNPV-Ts fed to neonates had the shortest or longest killing times, respectively, with ST₅₀ values of 6 and 19 days. AdhoNPV-To and AdorNPV-Ne had intermediate killing times. The OB yield per larva of AdhoNPV-Ts and AdhoNPV-To was significantly higher than that of AdorNPV-En and AdorNPV-Ne. Our results suggest that AdorNPV-En is suitable as an inundative agent because it is a quick-killing, highly virulent NPV, and AdhoNPV-Ts and AdhoNPV-To are more appropriately used as inoculative agents because of their high OB production.