The effect of the armored scale, Rhizaspidiotus donacis (Hemiptera: Diaspididae), on shoot growth of the invasive plant Arundo donax (Poaceae: Arundinoideae)

Abstract

The effect of feeding by the armored scale, Rhizaspidiotus donacis (Leonardi, 1920) (Hemiptera: Diaspididae) on the growth of the plant Arundo donax L. (Poaceae) was evaluated under field conditions in its native range. The study was designed to evaluate the impact of R. donacis, a candidate agent for biological control of A. donax which is invasive in arid riparian ecosystems of the Southwestern USA and Mexico. The study was carried out at five A. donax sites in the Province of Alicante, Spain, differing in altitude and climate. At each site, 30 infested lateral shoots were selected and 15 were randomly treated monthly with imidacloprid insecticide. Shoot lengths were measured monthly over a 1-year period in a comparative growth analysis. Shoots infested with R. donacis had an over 2-fold reduced growth rate as compared to treated shoots. Growth of shoots varied by site, and the effect of R. donacis on growth was most pronounced in the late spring, when mature females produced first instar scale crawlers. The impact of R. donacis on A. donax growth under field conditions in the native range, combined with its narrow host specificity, indicate that R. donacis is a promising candidate for biological control of A. donax in North America and other areas invaded by this weed.

Keywords:

• weed biological control
• native range studies
• giant reed
• growth rate

Acknowledgements

This work has benefited from the financial support of the project ‘Estudio de la biología de la cochinilla del Arundo’, ref. ‘USDA 1-10D’ from the United States Department of Agriculture, Agricultural Research Service and the U.S. Dept. of Homeland Security for the development of the Ph.D. of E.C.M. Alan Kirk (USDA-ARS, Montpellier, France); Rafael Cortés, Carolina Cortés, and Maria Dolores Mendoza are particularly thanked for their invaluable collaboration to the fieldwork. Anapaola Martínez, Raúl Briones and Olga Lucía Hernández are thanked for their help in some images and graphics of the presented work.