Potential of reduced-waxbloom oilseed Brassica for insect pest resistance

摘要

Insect pest and predator populations were field-sampled on three lines of Brassica napus L. and B. rapa L. with reduced crystalline surface waxes (waxblooms) and two B. napus with normal waxblooms. Seasonal per plant densities off the cabbage aphid, Brevicoryne brassicae L., were higher on normal waxbloom lines (range 6.0-8.2) than on reduced waxbloom lines (range 2.6-4.3) (P < 0.002). Two of the lines (closely related B. napus lines differing in waxbloom) were tested in a second year, and per plant densities of aphid colonies again were higher on the normal waxbloom line (15.2) than on the reduced waxbloom line (3.8) (P < 0.001). Flea beetle (Phyllotreta cruciferae) densities tended to be higher on reduced waxbloom lines, significantly so in the first season (P < 0.002). Densities of coccinellid adults and larvae were higher on the reduced waxbloom B. napus line only in the second year (P < 0.005). In the laboratory, attachment by adults of the dominant coccinellid, Hippodamia convergens Guerin-Meneville, was greater to leaf surfaces of the reduced waxbloom plants (P < 0.0001). Detrimental effects of genetically reduced waxbloom on plant growth and susceptibility to flea beetles would probably offset any advantages due to lower aphid populations on these plants. More moderate reductions in waxbloom produced by applications of the herbicide, S-ethyl dipropylthiocarbamate were not associated with any differences in insect populations in the field over two years.