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Rice ragged stunt virus (RRSV), which has been prevalent in South and Southeast Asia since 1977, caused typical symptoms on japonica rice, such as Kinmaze and Mihonishiki. However, barley, oat, wheat and maize, which had been known as hosts of rice black-streaked dwarf virus (RBSDV), were not susceptible to RRSV. The infected japonica rice developed symptoms of stunting, leaf twisting and vein swelling, that were identical to those caused by RBSDV.Other typical symptoms, such as nodal branching and ragged leaves, differed from those caused by RBSDV. A colony of Nilaparvata lugens collected in the fields of Japan and confined in the greenhouse for more than five years in Sapporo, Japan, was capable of transmitting RRSV in a persistent manner.Laodelphax striatellus, a vector of RBSDV, failed to transmit RRSV, and N. lugens, the vector of RRSV, did not carry RBSDV.RRSV was also carried by N. lugens when the insects were inoculated with the extracts from diseased rice plants and viruliferous insects by artificial injection. Purified preparations associated with the low infectivity contained numerous isometric particles of 36-40nm in diameter.The diameter of isometric particles in dip preparations varied from 44 to 63nm according to compounds used for fixing and staining.Electron micrographs of ultrathin sections showed abundant RRSV particles in phloem cells of infected rice leaves.The results suggest that RRSV and RBSDV are not identical, and although both may belong to the plant reovirus group, RRSV is probably a new member of planthopper-borne subgroup.

Rice tungo virus is tranmitted by Nephotettix impicticeps Ishihara but not by the closely related N. apicalis (Motsch.). Hybrids have been obtained from crosses between these two species. The morphological characteristics of the hybrids were not identical with either parent in respect to the marking on the abdomen of the nymphs, the submarginal black band on the vertex of the adults, or the number of teeth on the ventral surface of the aedeagus of the male genitalia. However, more than 10 per cent. of them, regardless of stage of development or sex, were able to transmit the tungo virus, indicating that the transmissive ability is inherited even in an interspecific cross. The virus seems to be nonpersistent in the hybrids as it is in N. impicticeps.

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The location of the tests did not affect results. In I'lorida, population pressure can be extreme resulting in 100% damaged plants in untreated checks. Materials and rates whidl prevented damage in one area of Florida gave comparable results in the other area with similar population pressure. REFERENCES CITED Brett, C. H. ]953. Fall armyworm control on late planted sweet corn.