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Differences Among Five Stages of Schizaphis graminum in Transmission of a Barley Yellow Dwarf Luteovirus. Guang- he Zhou, Visiting scholar and research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, Cornell University, Ithaca, NY 14853, Current address of senior author: Plant Protection Institute, Chinese Academy of Agricultural Sciences, Beijing, People' s Republic of China; W. F. Rochow, professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 74:1450-1453. Accepted for publication 12 July 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-1450.

The duration of each of four instars of Schizaphis graminum varied from 39 to 48 hr at 21 C, intervals that permitted direct comparison among all five stages as vectors of the SGV isolate of barley yellow dwarf virus. When aphids of each stage were allowed a 1-day acquisition feeding at 15 C and a 5-day inoculation test feeding at 21 C, percentages of first, second, third, and fourth instars and adults that transmitted virus were 36, 29, 11, 3, and 2, respectively. Extending inoculation test feedings to 10 days did not change the pattern of stepwise differences in SGV transmission by the five stages. Similar large differences also occurred when aphids acquired virus by feeding through stretched Parafilm membranes on concentrated inoculum, or by being injected with SGV. Use of combinations of temperatures from 15 to 30 C did not increase virus transmission by adults. Studies of virus latent periods in the vector suggested that adults were more likely to transmit SGV if they had acquired virus as nymphs. Combinations of long (5- 7 days) acquisition feeding periods with long (10 days) inoculation test feedings also resulted in more than occasional transmission by adults. The incremental pattern of virus transmission differences among the five stages suggests that the S. graminum-SGV system could be useful for basic studies of virus-vector interactions.