Comparison of sampling methods for alate aphids and observations on epidemiology of soybean mosaic virus in Nanjing, China.
Using standard diversity indices, samples of aphids collected on a vertical net were more diverse than collections from green pan traps in 1981. Some spp., notably Myzus persicae, Aphis citricola and Eriosoma japonicum, were collected in greater relative numbers in the pan traps. Several spp., including the Macrosiphoniella spp. were under-represented in the green pan traps presumably because they were not attracted to the green colour of the traps. Yellow pan traps, used concurrently to monitor landing rates of economic species, caught relatively more A. craccivora and M. persicae and relatively fewer A. gossypii than green ones. In Nanjing SMV usually spreads in spring-planted soyabeans during the second half of May, causing damage. The predominant aphid spp. trapped at that time were M. persicae, Lipaphis erysimi, A. gossypii, A. craccivora and E. japonicum, of which the first 4 are known vectors. Summer planted soyabeans are usually affected during a second period of virus spread in mid-Aug. when various Aphis spp. are abundant. The predominant vector of SMV at that time was thought to be A. glycines which colonises the crop; in 1981, however, A. citricola and A. gossypii, which do not colonise soyabean and A. craccivora, which rarely colonises soyabean, were much more abundant in mid-Aug. than A. glycines. A. citricola, A. gossypii and A. craccivora are all able to transmit SMV, and thus should be considered as potentially important vectors. In infectivity assays, only 4 of 1040 aphids transmitted SMV. These included an A. craccivora, 2 Toxoptera citricidus and an Aphis sp.