Comparative susceptibility of two different hosts to genotypic variants of the Anticarsia gemmatalis nuclear polyhedrosis virus

Abstract

The susceptibility of third instar larvae ofAnticarsia gemmatalis (Lepidoptera: Noctuidae) and Diatraea saccharalis (Lepidoptera: Pyralidae) to ten distinct plaque purified genotypic variants of a selected isolate of the Anticarsia gemmatalis multiple-embedded nuclear polyhedrosis virus (AgMNPV), was compared. Despite the fact that this isolate, AgMNPV-Ds20, represents a wild strain of the AgMNPV selected for higher virulence to D. saccharalis, an alternate host, most of the variants are much more virulent to the original host Anticarsia than to Diatraea. Bioassays have shown an over one hundred-fold variation in LD 50 values ranging from 1700 polyhedron inclusion bodies (PIBs) to more than 200 000 PIBs/larva. The PIB production in infected larvae increased with the pathogenicity of the variant to the host, showing an average ten-fold reduction in Diatraea when compared to Anticarsia for the same variant. The virus particle yield ranged from 6 x 10 7 to more than 10 9 PIBs/g of infected larvae in Diatraea and from 8x10 8 to more than 10 10 PIBs/g of infected Anticarsia larvae. The data show a clear difference of the pathogenicity of the genotypic variants of AgMNPV in vivo both between the original and alternate host and between the individual variants for the same host. These differences found in vivo indicate that monitoring of shifts in variant frequency of wild and laboratory-propagated viral isolates in these highly heterogeneous populations would help ensure the efficacy of biological control programs.