A small isometric virus has been isolated from larvae of the Guatemala potato tuber moth, Tecia solanivora (Povolny), collected in Ecuador. It was designated the Anchilibi virus (AnchV). The non-enveloped viral particles have an estimated diameter of 32+/-2 nm. Three major proteins were found in virions, with estimated sizes of 102.0+/-2.1, 95.8+/-2.0 and 92.4+/-1.5 kDa for AnchV as determined by polyacrylamide gel electrophoresis. After denaturing agarose gel electrophoresis, the genome of AnchV appeared to be a tri-segmented single-stranded RNA with fragment sizes of 4.1+/-0.2, 2.8+/-0.2 and 1.65+/-0.2 kb. In addition to a high virulence towards its original host, AnchV also caused high mortality in larvae of two other potato tuber moth species, Phthorimaea operculella (Zeller) and Symmetrischema (tangolias) plaesiosema (Turner). Electron microscopy confirmed that AnchV replication occurs in the cell cytoplasm, mainly in vesicles. Several important characteristics exhibited by this virus differ from those reported for known families of insect viruses. Thus, AnchV might be member of a new taxonomic group.