Transmission of Alternaria brassicicola to cabbage by flea beetles (Phyllotreta cruciferae)

In 1995 and 1996, flea beetles (Phyllotreta cruciferae) were observed in the field feeding on cabbage plants that were infected with Alternaria brassicicola. Flea beetles were captured in glass vials, etherized, and placed on agar media for isolation of A. brassicicola. In 1995, A. brassicicola was isolated from 13 out of 69 (18.8%) flea beetles in the first test and 38 out of 132 (28.8%) in the second test. In 1996, flea beetles were collected nine times during the growing season, and the isolation frequency increased from 0 to 77% as the crop approached maturity. In another study, flea beetles were collected from a field of A. brassicicola-infected cabbage, enclosed in plastic bags containing potted healthy cabbage plants, and then placed on a shaded greenhouse bench for 6 days. Alternaria leaf spot developed on plants that were infested with the contaminated flea beetles. Feces obtained from flea beetles that fed on cabbage infected with A. brassicicola contained intact and broken conidia of A. brassicicola and undigested pieces of cabbage leaf. The conidia were viable after passing through the flea beetles, as evidenced by their germination on the glass slides used for collecting the feces. Conidia of A. brassicicola were observed by scanning electron microscopy on all parts of flea beetle bodies, including wings, mouthparts, antennae, and legs.