Role of Predators in Regulation of Endemic Populations of Matsucoccus matsumurae (Homoptera: Margarodidae) in Japan

Abstract

Life table data for Matsucoccus matsumurae (Kuwana) were gathered from April through September 1984 from 30 ornamental and forest stands of two native hosts, Pinus densiflora Sieb. & Zucc. and P. thunbergiana Franco, and an exotic host, P. massoniana Lamb., located in central and southern Japan. The scale inhabited nearly every stand of the two Japanese pines, but its densities were always low and trees suffered no apparent injury. Trees were damaged, however, in forest stands of P. massoniana where densities were many times greater than on adjacent Japanese pines. Differences in scale abundance among host species and between forest and ornamental settings reflected differences in survivorship of first instars and fecundity of adult females. Population trend values calculated from life table data revealed that predators have an important role in the regulation of endemic populations of M. matsumurae. Harmonia axyridis Pallas, which comprised 84% of the total number of predators captured (n = 3,071), killed 97% of the scales in one heavily infested forest stand of P. massoniana in Kamigamo, Honshu in <4 weeks. When realistic densities of beetles were caged on infested pines, 81% of the small, inconspicuous stages of the scale and 98% of the larger, more conspicuous stages were consumed, which resulted in a 67-fold decrease in scale population growth compared with control cages containing no beetles. Despite prevalence of cannibalism among beetles both in cages and in the natural population, H. axyridis was clearly an effective regulatory agent for endemic populations of M. matsumurae and should be a prime candidate for biological control of exotic populations of this scale.