Interactions among convergent lady beetle (Hippodamia convergens) releases, aphid populations, and rose cultivar

Release of adult convergent lady beetles, Hippodamia convergens Guérin-Méneville (Coleoptera: Coccinellidae), provided inundative control of aphids (Homoptera: Aphididae) infesting Rosa hybrida outdoors in nursery containers and in the landscape. In potted roses, a single release of 100 lady beetles per 19 liter plant provided 66-88% aphid control during 1994 and 1995. In the landscape, a single release of about 175 or 350 lady beetles per 0.5-1 m tall shrub during 1994, 1995, and 2002 failed to reduce aphid density. However, each of one or two subsequent releases of about 1400-1750 H. convergens per shrub reduced aphid densities in the landscape to near zero (93-100% control). Releasing 10-20 beetles per flower bud controlled aphids on shoots caged to prevent insect dispersal. On uncaged rose shoots, 100 or more H. convergens per bud were required to control aphids. The effective rate for inundative release in landscape roses was about 2300 beetles/m2 (210/ft2) of shrub-covered surface, or two orders of magnitude greater than the 11-22 beetles/m2 (1-2/ft2) commonly recommended by beetle sellers. Based on three lady beetle releases during April-May when aphids are abundant on rose in California's Central Valley, lady beetle costs are about the same as one soil drench of the systemic insecticide imidacloprid. Rose cultivar affected aphid density, but cultivar did not affect augmentative predation. Cultivar selection and high-rate predator release are complimentary strategies for aphid management on rose.