Evaluation of Spanish arundo scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) survival and fecundity on three New World genotypes of Arundo donax (Poaceae: Arundinoideae)

Authors: Goolsby, John; CORTES MENDOZA, ELENA - Universidad De Alicante; Moran, Patrick; Adamczyk, John; MARCOS GARCIA, MARIANGELES - Universidad De Alicante; KIRK, ALAN - European Biological Control Laboratory (EBCL)

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2013
Publication Date: 2/11/2013
Citation: Goolsby, J.A., Cortes Mendoza, E., Moran, P.J., Adamczyk Jr., J.J., Marcos Garcia, M., Kirk, A.A. 2013. Evaluation of Spanish Arundo scale Rhizaspidiotus donacis (Hemiptera: Diaspididae) survival and fecundity on three New World genotypes of Arundo donax (Poaceae: Arundinoideae). Biocontrol Science and Technology. 23:499-506.

Interpretive Summary: Giant reed is a large (up to 25 ft tall) perennial grass from Mediterranean Europe, northern Africa, the Middle East and India that was introduced to North America by Spanish colonists hundreds of years ago for use in roofing and fences, and later for erosion control. However, giant reed has become a damaging invader in the southern U.S., especially in the Rio Grande Basin of Texas and Mexico, as well as in California. Giant reed forms dense thickets along rivers, canals and reservoirs, removing water that is needed for agriculture in regions where rainfall is scarce, and giant reed also promotes wildfires, displaces native plants and animals, and hinders access for border protection personnel. Several insects have been imported from Mediterranean Europe for evaluation and possible release for biological control of giant reed. One of these insects is a tiny ‘armored scale’, which spends most of its life in an immobile state, forming a waxy protective cover over its body while it sits on stems and roots of giant reed and sucks juices out of the tissues with its needle-like mouth. We determined that armored scales collected from southeastern coastal Spain, on the Mediterranean Sea, develop larger populations and produce more offspring when given the opportunity to infest the giant reed plants that are the dominant invasive type in the Lower Rio Grande Basin. These plants have been shown, through DNA fingerprinting, to come from the same region of Spain as the armored scales. Armored scales that infested giant reed plants with a ‘fingerprint’ suggestive of an origin in India or nearby (collected as an invasive plant in West Texas) developed first-generation populations that were 33% smaller and second-generation populations up to 50-fold smaller than did scales on Spanish plants. Production of second-generation ‘crawlers’ by first-generation females did not vary between the two types of giant reed plants. However, crawlers may have had an easier time settling into the immobile stage on Spanish plants than on Indian plants. These results demonstrate the importance of determining the point of origin of a weed invasion, so that beneficial insects from the same geographic area are collected and released, to maximize the effectiveness of weed biological control.

Technical Abstract: A pre-release evaluation of survival and fecundity of the arundo scale, Rhizaspidiotus donacis, was conducted on three invasive genotypes of the riparian weed, Arundo donax. The three A. donax genotypes were collected from Laredo, Austin and Balmorhea, TX, which represented the majority of the genotypic diversity found in Texas watersheds. Although Rhizaspidiotus donacis developed on all three genotypes of the plant, the Austin A. donax genotype, followed by the Laredo genotype, were the most suitable in terms of the size of immature and adult scale populations that developed after crawler release. Both the Laredo and Austin genotypes of A. donax, likely to be of Spanish origin, are close genetic matches with scale’s original host plant genotype in Alicante, Spain. In comparison, survival was lowest on the phylogenetically distant genotype of A. donax from Balmorhea, TX. Although the population size of settled, immature second-generation scales varied in a manner similar to that of the first generation, the fecundity of isolated first-generation females was not significantly different across the three plant genotypes, suggesting that R. donacis is not a genotype specialist in terms of nutrient assimilation for reproduction. Rather, differences in genotype suitability may manifest at the crawler settling stage. These results indicate that selection of scale genotype from the native range may have a moderate influence on the success of R. donacis and ultimately the biological control program.