ABSTRACT
The South American soybean pest, Rachiplusia nu (Guenée), is naturally infected by Autographa californica multiple nucleopolyhedrovirus (AcMNPV) and Rachiplusia nu nucleopolyhedrovirus (RanuNPV). We compared their pathogenicity to fourth-instar R. nu larvae, by evaluating time to death and virus spread throughout the tissues in single and mixed infections. Bioassays showed that generalist AcMNPV had a faster speed of kill than specific RanuNPV, while the mixed-virus treatment did not statistically differ from AcMNPV alone. Histopathology evidenced similar tissue tropism for both viruses, but co-inoculation resulted in mostly AcMNPV-infected cells. In sequential inoculations, however, the first virus administered predominated over the second one. Implications on baculovirus interactions and biocontrol potential are discussed.
Subject(s)
Lepidoptera , Moths , Nucleopolyhedroviruses , Animals , Larva , Spodoptera , VirulenceABSTRACT
Rachiplusia nu (Lepidoptera: Noctuidae) is a key soybean pest in Argentina. Current management of this moth relies mainly on the use of synthetic insecticides and transgenic plants. In search of biological control-based alternatives, a baculovirus from R. nu (hereafter RanuNPV) was characterized and its insecticidal properties tested under laboratory conditions. RanuNPV occlusion bodies (OBs) were nearly tetrahedral, averaging 1.0⯱â¯0.2⯵m in their longest edge and containing singly enveloped nucleocapsids. Histopathology of infected late-instar larvae revealed broad tissue tropism, where fat bodies and epidermis were the most affected organs. Phylogenetic analysis of concatenated polh, lef-8 and lef-9 partial sequences classified RanuNPV as a new species that clusters with other group II alphabaculoviruses infecting larvae of Plusiinae. Bioassays performed with R. nu neonates determined the median lethal dosage to be approximately 2.5â¯OBs/larva; most insects died within 4-5â¯days post inoculation showing typical baculovirus-induced liquefaction. No effects were observed in other lepidopteran species assayed, including Spodoptera frugiperda, Cydia pomonella and Diatraea saccharalis. High pathogenicity and host specificity make RanuNPV a good candidate for controlling R. nu.