First Report of Japanese Beetle (Popillia japonica) as a Vector of Southern bean mosaic virus and Bean pod mottle virus.

The Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae), was introduced into the United States in New Jersey in 1916 and now commonly occurs in the eastern and mid-western United States. The Japanese beetle has a wide host range and feeds on more than 300 plant species within 79 families (2), but it has not been reported to be a vector of plant viruses. Southern bean mosaic virus (SBMV; genus Sobemovirus) and Bean pod mottle virus (BPMV; family Comoviridae, genus Comovirus) are transmitted by several species of leaf-feeding beetles in the families Coccinelidae and Chrysomelidae (1). Japanese beetles, collected in northwestern Arkansas with a JB Jumbo insect trap (Great Lakes IPM, Inc., Vestaburg, MI), were tested to determine if they are able to transmit SBMV and BPMV. The beetles were given a 24-h acquisition access (individually in plastic petri dishes) to detached trifoliolate leaves of Phaseolus vulgaris 'Black Valentine' systemically infected with either BPMV or SBMV. Beetles that had fed on the infected bean leaves (as evidenced by feeding damage to the leaves) were caged individually in clear plastic cups on healthy 'Black Valentine' bean seedlings for a 24-h transmission access period. The test plants were grown in the greenhouse for 2 weeks after which they were evaluated for virus infection. In the first trial, BPMV was not transmitted (0 of 11 bait plants with feeding damage), whereas SBMV was efficiently transmitted (6 of 6 bait plants with feeding damage) as determined by agar-gel double-diffusion serology of test plants using polyclonal antibodies to SBMV and BPMV. In a second trial, with a different set of beetles, the transmission rate for BPMV was 3 of 46 (6.5%) and 33 of 43 (77%) for SBMV, and the test plants were evaluated for virus infection using Protein A ELISA. The higher transmission efficiency of SBMV by Japanese beetles when compared with BPMV is characteristic of these two viruses when they are transmitted by other leaffeeding beetles (1). These results are in contrast to an earlier report that Japanese beetles were not able to transmit BPMV from infected soybeans to healthy soybeans in Illinois (3). To our knowledge, this is the first report that the Japanese beetle, an introduced insect with a wide host range in the United States, is a vector of plant viruses. References: (1) J. P. Fulton et al. Ann. Rev. Phytopathol. 25:111. 1987. (2) D. W. Held. J. Aboricult. 30:328, 2004. (3) T. R. Mabry et al. Plant Dis. 87:1221, 2003.