Use of flowering resource plants for conservation biological control of euonymus scale

Eric J Rebek, Purdue University

Abstract

Flowering resource plants were used to assess their ability to conserve natural enemies of euonymus scale, Unaspis euonymi (Comstock) (Homoptera: Diaspididae), and alter its population dynamics. The experimental landscape consisted of 1-m2 plots of Euonymus fortunei (Turcz.) infested with euonymus scale, a noxious pest of woody ornamental plants. Plot treatments contained either low or high densities of perennial flowering plants known to attract predators and parasitoids, or were surrounded only by wood mulch, which served as the control. Four species of perennial flowering plants with overlapping bloom periods were chosen to provide nectar and pollen throughout the summer months. Yellow sticky cards and a vacuum sampler were used to collect arthropods from research plots. Euonymus plots surrounded by flowering plants typically attracted a larger number of natural enemies than those surrounded only by mulch. Araneae and parasitic Hymenoptera were most abundant in plots containing flowering plants. Removing flowers from plants had no effect on the abundance and spatial distribution of natural enemies. The amount of plant biomass contained within flowering plant plots was positively correlated with the abundance of parasitic wasps and total natural enemies. These results suggest that vegetational rather than floral components of plants were most influential to natural enemy abundance. Scale population densities were lower in plots surrounded by flowering resource plants than in plots without flowers. Regardless of treatment, densities of scale insects parasitized by Encarsia citrina (Craw.) (Hymenoptera: Aphelinidae) were often positively correlated with total densities of scales available. Parasitism rates were not influenced by treatments and within-generation correlations between parasitism rate and total scale density were usually not significant. However, high parasitism rates were occasionally correlated with low densities of scales in the subsequent generation. Neither the amount of flowers themselves nor flowering plant biomass were associated with parasitism rate or scale density. The combined results indicate euonymus scale populations were likely influenced by a combination of parasitism by E. citrina and some unknown factor(s) unrelated to the presence of flowering plants.

Degree

Ph.D.

Advisors

Sadof, Purdue University.

Subject Area

Entomology

COinS