Data From: Establishment And Dispersal Of The Armored Scale Rhizaspidiotus Donacis For Biological Control Of Arundo Donax In Northern California.

Abstract from paper: The rhizome-, shoot- and leaf-feeding armoured scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) was released for biological control of invasive arundo (Arundo donax) in the Sacramento and San Joaquin River watersheds of the Central Valley of northern California. One year after release, short-term establishment of R. donacis was confirmed at all nine field sites (11 release sites). Four to eight years after release, 47% of the nodes of side shoots removed from live main shoots in the release plots at the nine field sites supported at least one adult female of R. donacis, verifying long-term establishment, and at five sites \100% of the plots examined had established populations. Pre-release mechanical control of A. donax (ground-cutting, mowing or no cutting) did not influence short or long-term establishment. To determine dispersal of R. donacis, side shoot nodes were examined at various distances from 16 plots across eight sites. Scale prevalence and abundance were negatively related to distance from release plot. Reproductive adult females dispersed 10 m or less from 13 of these plots, with annual dispersal under 2 m per year, consistent with general expectations of armoured scale crawler active dispersal ability, and maximum dispersal distance was not dependent on scale density in the release plot. Dispersal between 40–73 m in two plots was possibly caused by disturbance. The armoured scale R. donacis was confirmed as being well-established, dispersing and building populations, with potential to negatively impact A. donax.

Full citation for paper: Moran PJ, Valle DV, Bitume EV, Portman SL, Goolsby JA. 2025. Establishment and dispersal of the armored scale Rhizaspidiotus donacis for biological control of Arundo donax in northern California. Biocontrol Science and Technology 35(7): 755-776. https://www.doi.org/10.1080/09583157.2025.2514451.

Who: Studies led by Dr. Patrick J. Moran, retired Research Entomologist, USDA-ARS, Invasive Species and Pollinator Health Research Unit (ISPH), Albany, CA. Dr. Moran conceived the studies, obtained funding, designed and conducted studies, acquired data, curated and analyzed data, wrote the original draft of the manuscript and made all revisions and editing after peer-review and review of page proofs. Other participants included D. Valle Rogers, former temporary employee, ARS-ISPH and currently a Ph.D. student at UC-Berkeley (Study design, data acquisition and data curation, and review/editing of the manuscript); Dr. Ellyn V. Bitume, former postdoc at ARS-ISPH and now a former Research Entomologist with the USDA-Forest Service, Southwest Pacific Research Station, Institute of Pacific Islands Forestry, Hilo, HI (data acquisition, data analysis, review and editing of manuscript; Dr. Scott L. Portman, Entomologist, ARS-ISPH (study design, data acquisition); and Dr. John A. Goolsby, retired Research Entomologist, USDA-ARS Cattle Fever Tick Research Unit, Edinburg, TX (Study design, provision of biological materials for studies-insects for field release for weed biocontrol).

What: Release of the armored scale insect Rhizaspidiotus donacis (Hemiptera:Diaspididae) for biological control of the invasive giant grass known as arundo, giant reed or carrizocane (Arundo donax), and monitoring of its establishment and local dispersal. This armored scale was previously released in southern Texas and in Mexico, and has been considered for release in South Africa, Australia and New Zealand. It is the first diaspidid armored scale in the world to be intentionally released for biological weed control. The dataset consists of summarized weather data from raw data obtained from online databases; summarized soil type data for each site from an online database; data for plot pre-release cutting treatment and short-term establishment (counts of females removed from rhizomes and counts of neonate crawlers they produced when isolated in the lab, as well as prevalence of successfully established release plots for each site); data for long-term establishment (counts of the number of side shoot nodes examined, number of nodes with at least one adult female, and prevalence of release plots with at least one scale-infested node per site); and dispersal data shown two ways: Vertically by site, dispersal transect origin (release plot), distance from plot, prevalence of scale-infested nodes, number and density of adult females per node dissected in the lab, counts of crawlers they produced, and production per female isolated; and horizontally by site and transect origin, to summarize total females isolated, maximum dispersal distance, and calculated dispersal per year based on knowledge of the year of scale release.

When: Releases were initiated in 2015, but at most sites the main year for releases was 2017 or 2018, with releases at two sites in 2019. Monitoring of short-term establishment success was conducted one year after release at each site (between 2016 and 2020) by examining rhizomes (tuber-like roots) of arundo plants in release plots for the presence and density of adult scale females. Monitoring for long-term establishment took place 4 to 8 years after release (2022-2023) by examining and dissecting nodes of side shoots withint the release plots for adult females. Monitoring of dispersal was conducted in 2024 at all sites, by examining side shoot nodes outside of the release plots at various distances.

Why: The only two prior studies of establishment of the scale (in Texas) involved either 25 sites but only yes/no determination of establishment at each site; or, involved only two sites. No prior study of the establishment of the scale had been conducted in the Central Valley of northern California, where arundo threatens water resources. No prior study had quantitatively examined both short- and long-term establishment of the scale. No prior study in the world had ever examined active (by crawlers) field dispersal of this scale species.

How: See the Materials and Methods section of the paper, and Supplemental Information available with the paper, for information on methods.
Organization: Department of Agriculture
Last updated: 2025-08-05T19:03:58.268477
Tags: armored-scale, arundo-donax, biological-control, diaspididae, dispersal, establishment