Variegation in Coleus blumei and the Life History of Citrus Mealybug (Homoptera: Pseudococcidae)

Abstract

Three leaf-color variants of Coleus blumei ‘Bellevue’ (Bentham) were studied to determine the effects of variegation-induced changes in host-plant quality on life history and population growth of citrus mealybug, Planococcus citri (Risso). Compared with green counterparts, both red- and yellow-variegated plants of C. blumei grew more slowly, had lower rates of photosynthesis, and produced more leaf area per unit of biomass. All life history parameters of citrus mealybug were affected differentially by presence and type of variegation, with the exception of egg hatch rate and female reproductive time. Nymphs developed most rapidly and adult females produced the most eggs on red-variegated plants. Mortality of nymphs was significantly higher on green plants than on red- or yellow-variegated plants. Overall, the higher intrinsic rate of increase for citrus mealybug populations on red or yellow plants indicated that variegated plants were more suitable hosts tllan green plants. Increased population growth of citrus mealybug, in turn, killed red- and yellow-variegated plants sooner than green plants when they were infested with a similar number of crawlers. This study suggested that a horticulturally important feature, such as variegation, can increase the abundance of insect pests on host plants and make them more vulnerable to pest injury.