Effects of variegation in Coleus blumei (Bentham) on Planococcus citri Risso (Homoptera: Pseudococcidae) and its parasitoid Leptomastix dactylopii Howard (Hymenoptera: Encyrtidae)

Jinsong Yang, Purdue University

Abstract

Red, yellow, and green-leafed varieties of Coleus blumei (Bentham) were studied to determine effects of plant variegation on life history and population growth of the citrus mealybug and its parasitoid Leptomastix dactylopii. Compared with green counterparts, plants with either red or yellow variegated leaves grew more slowly, had lower photosynthetic rates, and produced more new leaf area per unit of accumulated biomass. Life history parameters of citrus mealybug and its parasitoid were differentially affected by the presence and type of variegation. Higher intrinsic rates (r$\sb{\rm m}$) of increase for citrus mealybug on red and yellow plants indicated that variegated plants were better host plants than green plants. When L. dactylopii parasitized same-aged 4th instar mealybug females on red and green plants, developing parasitoid larvae had a greater survivorship and a female biased sex ratio compared with yellow plants. The emerging adult female parasitoid were larger and tended to produce more eggs. Intrinsic rate (r$\sb{\rm m}$) of increase for the parasitoid was higher on red and green plants than on yellow plants. This was attributed to the larger size of citrus mealybugs on green and red plants when compared with those on yellow plants. Variegation-mediated morphological changes on host plants directly affected host discovery by L. dactylopii. Red and yellow variegated plants were shorter, had less plant surface area but more leaves per unit of plant height compared with green plants. Initial host plant preference by parasitoids was not affected by leaf color variegation on either infested or uninfested plants. Lower average parasitism rates of citrus mealybug on variegated plants suggests that the complexity of the plant structure created by the larger numbers of leaves was more important than plant surface area in determining searching efficiency of the parasitoid. This study suggests that the horticulturally important feature, variegation, has the potential to increase pest abundance and to make host plants more vulnerable to injury.

Degree

Ph.D.

Advisors

Sadof, Purdue University.

Subject Area

Ecology|Entomology

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