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Title: Density-dependent impacts of the arundo scale (Rhizaspidiotus donacis) on the productivity and physiology of giant reed

Author
item Racelis, Alexis
item Moran, Patrick
item Yang, Chenghai
item Goolsby, John

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/10/2011
Publication Date: 10/15/2011
Citation: Racelis, A.E., Moran, P.J., Yang, C., Goolsby, J. 2011. Density-dependent impacts of the arundo scale (Rhizaspidiotus donacis) on the productivity and physiology of giant reed. Meeting Abstract. CDROM.

Interpretive Summary:

Technical Abstract: The armored arundo scale, Rhizaspidiotus donacis (Homoptera: Diaspididae) has been permitted for a biological control agent to control invasive populations of giant reed (Arundo donax L.). A non-native, highly invasive woody grass, giant reed infests waterways and riparian areas of the southwestern US and Mexico by competitively displacing neighboring vegetation through prolific water use and prolific growth. To test the hypothesis that pressure from natural enemies can reduce competitive abilities of weeds, we use a nested factorial design within a controlled greenhouse setting to examine if infestations of R. donacis can interrupt the net primary production of giant reed and detrimentally affect the photosynthetic ability of the plant. Different densities of the immature stages of two distinct genotypes of the arundo scale were administered to individually-potted ramets of the same genotype of the target weed. Growth parameters of plant such as shoot height and number of nodes, number of shoots, number and length of side shoots were measured monthly for six months, or after one generation of the scale. Insect-induced plant physiological stress was estimated with monthly measurements of light reflectance using a spectroradiometer, and by analyzing differences in leaf gas exchange among the different treatments at the end of the experiment. At six months, all plants were destructively sampled to count the density of mature scale adults and to extrapolate biomass accumulation of the test plants. Initial results suggest a scale density-dependent effect on both plant biomass and water use efficiency. Potted plants that have a high administered density of immature scale tend to have a slower rate of growth than control plants and plants with low doses of insects. If this trend continues, this biological control agent may prove to be an effective tool to curb the negative ecological and social impacts of this weed. These results can be used as a predictive tool of the density dependant impacts of the arundo scale on plant growth and transpiration, ultimately informing an inundative biological control program approach to weed biological control.