Effects of Brassica oleracea waxblooms on predation and attachment by Hippodamia convergens

Four mutations that reduce waxbloom in Brassica oleracea L. were examined for their effects on predation, mobility, and adhesion to the plant surface by the general predator Hippodamia convergens (Guérin-Menéville) (Coleoptera: Coccinellidae). The mutations reduce waxbloom to different degrees, but all produce a glossy phenotype. Plants tested were inbred lines, near isogenic lines, or segregating F₂ populations, depending on the mutation. In an experiment on caged leaves, predation of Plutella xylostella L. larvae by H. convergens adult females was significantly greater on glossy types as compared with normal-wax or wild-type counterparts. Although the trend was the same for each mutation, individual comparisons between glossy and normal-wax lines or segregants were only significant for two of them, those producing mutant alleles gl_a and gl_d. Individual H. convergens were observed to spend more time walking on leaf edges and less time walking on leaf surfaces of normal-wax plants than glossy plants. Hippodamia convergens also obtained better adhesion to the surfaces of glossy plants than to normal-wax plants when tested using a centrifugal device. Two of the mutations produced similarly strong effects on predation, behaviour, and adhesion by H. convergens. These two are the same previously determined by us to provide the strongest similar effects on another generalist predator, Chrysoperla plorabunda (Fitch). The results indicate that waxbloom variation in nature could affect herbivore populations through its effects on generalist predators.