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 found to be more diverse than collections from green pan traps in experiments conducted in Nanjing, China in 1981. Some species, notably Myzuspersicae, Aphis citricola, and Eriosoma (Schizoneura) japonicum, were collected in greater relative numbers in the pan traps. Several species, 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 Aphis craccivora and M. persicae and relatively fewer Aphis gossypii than green ones. In the Nanjing area soybean mosaic virus (SMV) usually spreads in spring planted soybeans during the latter half of May, causing damage. The predominant aphid species trapped at that time were M. persicae, Lipaphis erysimi, A. gossypii, A. craccivora and E. japonicum, of which the first four are known vectors. Summer planted soybeans are usually affected during a second period of virus spread occurring in mid-August when various Aphis spp. are abundant. The predominant vector of SMV at that time was thought to be Aphis glycines which colonises the crop; in 1981, however, A. citricola and A. gossypii, which do not colonise soybean and A. craccivora. which rarely colonises soybean, were much more abundant in mid-August 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 four of 1040 aphids transmitted SMV. These included an A. craccivora, two Toxoptera citricidus and one Aphis sp.