Three insects are permitted for release as biological control agents of arundo, or giant reed, including the shoot tip-galling wasp Tetramesa romana (Hymenoptera: Eurytomidae), the rhizome- and shoot-feeding armored scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), and the arundo leafminer (Lasioptera donacis) (Diptera: Cecidomyiidae).

The arundo wasp is native to Mediterranean Europe (Marshall et al. 2018). This small (1/8th to 1/4th inch long), black wasp (Fig. 1) is harmless to humans and animals. The female wasp curls its abdomen and lays eggs (Fig. 2) in the stem near shoot tips with its needle-like ovipositor, which stimulates the formation of galls in which the larvae develop. The wasp can develop only on arundo (Goolsby and Moran 2009, Goolsby et al. 2020). The adults are almost all females, and they can reproduce without mating. Adults live 2 to 5 days and can produce an average of 26 offspring (Moran and Goolsby 2009). Pupation occurs inside the gall, and adults chew a small, round ‘exit hole’ to emerge from the gall (Fig. 3). Looking for and counting exit holes is the easiest way to diagnose the wasp’s presence and to determine its abundance. The wasp life cycle takes about 33 days at 80 °F and 50-60 days under variable field conditions between 60-90 °F. Pupae and adults can survive both prolonged drought and winter conditions inside galled shoot tips before emerging. In northern California, the arundo wasp has been released since 2010 at four sites on private land in along Stony Creek in the Sacramento River watershed (Orland, Glenn County); since 2015 at one site in eastern Contra Costa County near Oakley (Big Break Regional Park); at two sites in Sacramento County near Rio Vista and Walnut Grove along the Sacramento River; and, since 2017 at nine sites extending from Orland in the northern Sacramento River watershed to Berenda Slough and Cottonwood Creek near Madera, in Madera County in the southern San Joaquin watershed. Two years after 2017 releases, reproductive populations of arundo wasps were observed in the summer of 2019 at one site each in Orland, Glenn County, and in Madera, Madera County. It is too early to evaluate the impact of the arundo wasp in California. Seven years after initial release in Texas, it has had moderate impact, reducing live biomass (weight) of arundo shoots 30-40%, leading to a two-to-four fold increase in the abundance of native plants (Goolsby et al.2016; Moran et al.2017). Adventive (accidentally introduced) populations of the arundo wasp have been found in Santa Barbara, Ventura, Los Angeles, Orange, San Diego, and San Bernardino counties in coastal watersheds (Dudley et al.2008).

The arundo armored scale feeds and reproduces solely on arundo in the field (Goolsby et al. 2009, 2020). Adult females (Fig. 4) are about 1/16th of an inch in size, and are immobile, with no legs or antennae. They use their stylet-like mouthparts to suck fluids from the vascular tissues of tuber-like arundo rhizomes (roots) (Fig. 5, 6) and the bases of the shoots (Fig. 7). Adults produce tiny (less than 1/32th inch long) crawlers, which disperse a few feet at most before settling at a permanent feeding site. Each adult female can produce 85 crawlers on average (Moran and Goolsby 2010). Crawlers secrete a white waxy covering and molt to a second immature stage, which secretes a brown scale covering (Fig. 4) and continues to develop. Adult males emerge about 6 to 8 weeks after the crawler stage. The short-lived, winged adult males mate with immobile adult females. These females then expand their bodies over 2-fold in size as they continue to feed and develop crawler embryos (Fig. 4). The total life cycle of the female requires five to six months (Moran and Goolsby 2010). The scale is established at release plots at several sites in southern Texas. Combined with the wasp, the scale is having moderate impact in these plots, reducing live shoot biomass by up to 50% compared to plots with the wasp alone (Goolsby and Moran 2019). Initial establishment of the arundo armored scale is typically seen as sparse populations on rhizomes (Fig. 6), but over time, dense populations can develop on rhizomes (Fig. 5), and on the bases of shoots, causing a ‘witches broom’ distortion symptom (Fig. 7).

The arundo armored scale was first released in northern California in 2014-2015 at several sites along Stony Creek near Orland in Glenn County. In 2017-2018, armored scales were released at seven sites, two near Orland; two near Rio Vista and Walnut Grove along the Sacramento River (Sacramento County); and three on Berenda Slough and Cottonwood Creek near Madera (Madera County). In 2019, establishment of sparse populations of reproductive females was confirmed in at least one release plot at all seven sites. Adult females were found on resident arundo rhizomes, and the females produced crawlers in the lab, indicating that more unsampled adult females are likely producing crawlers at the field sites. In 2018, an adventive population of the arundo armored scale was found in the Santa Clarita River drainage in Ventura County (A. Lambert and T. Dudley, UC Santa Barbara, unpubl. data).

Dispersal of the armored scale is far slower than for the wasp, and so long-term impact is likely to be localized to release plots until flooding events or other disturbances distribute the scale throughout watersheds.

The arundo leafminer is a tiny, mosquito-like insect (Fig. 8) that is host-specific (Goolsby et al 2017) and mines the leaf sheaths of arundo. It is permitted for release in the USA, but has not yet been released due to difficulties in rearing adults outside of the lab. This insect is not currently available for release in California.

The arundo aphid, Melanaphis donacis (Hemiptera: Aphididae), is present in California as an adventive (accidentally introduced) natural enemy. The aphid appears to be widespread, but its actual distribution and impact in California are unknown. It is visible as small (1/16th inch), white, waxy or powdery adults and smaller immatures (nymphs) mostly on the underside of arundo leaves. Infested leaves and others nearby become sticky with the ‘honeydew’ excreted by the aphids. This aphid is parasitized by various parasitic wasps, turning the adults into round, brown ‘mummies’ from which wasps emerge. The arundo aphid is not permitted by the California Department of Food and Agriculture for redistribution and use as a biological control organism in California.

Biological Control Agents


Common name




Tetramesa romana

Arundo wasp



First released in n CA in 2010, adventive in southern California

Rhizaspidiotus donacis

Arundo armored scale



First released in n CA in 2014, adventive in Ventura County

Lasioptera donacis

Arundo leafminer

none in field


Approved for release in USA. Not yet released.

Melanaphis donacis

Arundo aphid



Adventive. Not a permitted agent.

1Too early to evaluate impact in northern California. Impact demonstrated in Texas.

How the Technique Is Employed

Field sites should be surveyed to determine if the arundo wasp and armored scale are present. If the insects are already present, there is no benefit to releasing more.

The arundo wasp can be sampled most easily by standing in one place in the arundo patch for 2 minutes and counting all exit holes visible in a 360-degree turn, then repeat at at least five locations at the site, spaced at least 30 ft. apart. Because the wasp makes galls on shoot tips, most exit holes (Fig. 3) will be at head height or higher on side shoots. If you see young main shoots (less than 2’ tall) in the understory with galls, with or without exit holes, this is clear evidence of establishment of a large arundo wasp population. Galled young main shoots will be bent at an abrupt angle and can thus be distinguished from non-galled main shoots, even if no exit holes are present.

Arundo wasps can be released as piles of shoots with fresh galls (without exit holes or just a few holes) cut from established sites, transported to new sites and laid on the ground near arundo; or as adults collected from galls in the laboratory and released as adults. To collect adults, strip leaves off of galled main shoot pieces (approx. 18 inches long), or axils with live galled side shoots. Avoid collecting side shoots with many exit holes, as they will no longer contain adults. Wax the cut ends of the shoots with paraffin (e.g., Gulf Wax) melted under low heat. This step helps retain moisture in the galls. Place galled shoots vertically into an emergence container such as a Plexiglas cage or large clear plastic or cardboard bin. Use an insect aspirator to collect adults every other day. Check collections for other insects and remove them. Arundo wasps can be easily distinguished from other insects by their black bodies, pointed abdomens, and long antennae with ‘rings’ on the females (Fig. 1). If needed, wasps can be stored in plastic vials for one week in a refrigerator without food. When transporting vials to the field site, allow wasps to warm to room temperature, but protect from sunlight and excessive heat. Release by opening the vial on leaves near arundo shoot tips. The best season for conducting arundo wasp releases is April through July.

The arundo armored scale is most easily sampled by scraping back a little gravel or dirt from the base of buds on rhizomes that are six months to one year old (Fig. 6). These rhizomes can be found near the edge of arundo patches underneath live, mature (with inflorescence tufts) shoots. Peel back the dead, pointy leaf-like structures attached to the rhizomes and look for adult female scales on the rhizome or look on shoot buds or the bases of shoots. If scales are seen, rhizome samples can be cut with a powered reciprocating saw or hand saw and levered out of the ground with a shovel for further examination. A light microscope at 10X power is required to count the females, and the much smaller male scales can usually be seen as brownish spots attached to the female scales. Arundo patches with well-established wasp and armored scale populations will lack vigor (see banner image). One-half or more of the main stems will be dead or dying. Live main shoots with dead/broken off side shoots will be common. Female arundo scales may be present on side shoots (Fig. 7) as well as on rhizomes (Fig. 5, 6), and tiny males will be present on leaf collars. It will be possible to easily see through the stand, as opposed to the impenetrable ‘wall’ formed by vigorous arundo. Other factors such as drought can decrease vigor as well; however, so it is always best to sample for insects to confirm their presence.

The arundo armored scale can be released most easily by digging up pieces of infested rhizome (about the size of a baseball), cutting off roots on the underside, transporting them to the new site and positioning them on the edge of arundo patches. Scrape back the soil to expose pink or light brown buds and the tops of rhizomes, then position the infested rhizome pieces near the exposed resident rhizomes. Mark release locations with flagging tape or pin flags. Cover rhizome pieces and exposed recipient buds and rhizomes with a light layer of mulch (i.e. dead arundo leaf material) to provide some protection against heat and desiccation of the scales. The best time to conduct armored scale releases is late fall through winter (November through March).

Special Tips

The arundo wasp performs best when there are abundant young side shoots less than 4 inches in length and a few to abundant young main shoots (no more than 2’tall), as each shoot provides a tip on which the wasp can deposit eggs. To enhance production of shoot tips prior to wasp release, ‘top’ (mow) plots (e.g., 7’ x 7’) with hand loppers or a power tool to 5’ (chest) height (Fig. 9), or cut plots with loppers to ground level. Cutting should be done in spring in soil that is at least somewhat moist (e.g, March in southern CA, April in northern CA). Remove debris from the plot to allow room and sun for new shoot growth. If cutting must be done in the summer or fall, watering of the plots after cutting is recommended to encourage regrowth. Mark plot locations with flagging tape or pin flags. The ‘topping’ technique produces more vigorous, bushy, dense regrowth of side shoots (Fig. 10) than does ground-cutting, which leads to production of new main shoots (Fig. 11). A ‘double-cut’ technique, in which plots are first cut to ground level in early spring and then ‘topped’ 2 to 3 months later, may produce an optimal mix of main and lateral shoots. Release arundo wasps as either galled shoots or adults, beginning four weeks after final cutting. Releases may continue for 1 to 2 months following initial release. If no pre-cutting is done, release galls/wasps in the spring to early summer in stands of arundo with 5 to 15 ft-tall main shoots that are producing abundant new side shoots. Check the plots for eatablishment every 2 months (except in winter) using the 2-minute count technique.

The arundo armored scale will also benefit from ‘topping’ or ground-cutting arundo prior to its release, as this pre-treatment will induce production of new shoot buds. Releases should be conducted in the fall-winter time frame noted above, six months after spring cutting. If no pre-cutting is done, conduct releases near the edges of arundo stands, where there are young buds suitable for colonization. Collect a small sample of rhizome (e.g. 6” x 6 “ square) from each release point annually beginning one year after release and examine as noted above. Beginning two years after release, establishment can also be checked more rapidly by counting the number of leaf collars within 3’ or 4’ of the release point that have male scales, and expanding outward each year if males are seen.

Biological control of arundo can be complementary to herbicide treatments or mechanical control, especially if there are areas that escape the treatment (too difficult to access or too environmentally sensitive). Leave plots of the arundo untreated (at least 7’ x 7’ square) for biological control releases


No Federal or state permits are required to move the arundo biological control agents within California, but various landowners/agencies may have their own permitting requirements for releases on their lands.

Do not treat arundo chemically, mechanically or with fire at locations at which the biocontrol agents have recently (within the past year) been released. When releasing the arundo wasp and scale, avoid sites/plots subject to winter flooding. However, once they are well established, both insects will likely persist after flooding. Check sites for signs of the wasp and scale after floodwaters recede.

Insecticide drift from applications to crops can limit arundo wasp establishment, and many arundo-invaded waterways are adjacent to crops.

Where Can I Get These?

There are currently no commercial sources for the arundo wasp or scale in California. A landowner that has existing populations may be willing to act as a ‘donor’ for arundo wasp and armored scale populations. There are currently only two known sites (one in Glenn County and one in Madera County) with established populations of both agents in northern/central California. Contact the USDA-ARS author listed above. Wasp availability varies greatly by season, with late winter through early summer being the best time to collect galled shoots.


Dudley, T.L., A.M. Lambert, A. Kirk, and Y. Kawagama. 2008. Herbivores associated with Arundo donax in California. In: Julien, M.H., Sforza, R., Bon, M.C., Evans, H.C., Hatcher, P.E., Hinz, H.L., & Rector, B.G. (eds.), Proceedings of the XII International Symposium on Biological Control of Weeds. CAB International Wallingford, UK, pp. 138-144.

Goolsby, J.A. and P.J. Moran. 2009. Host range of Tetramesa romana Walker (Hymenoptera: Eurytomidae), a potential biological control of giant reed, Arundo donax L. in North America. Biol. Cont. 49: 160-168. doi:10.1016/j.biocontrol.2009.01.019

Goolsby, J.A. and P.J. Moran 2019.Field impacts of the arundo scale, Rhizaspidiotus donacis (Homoptera: Diaspididae) on Arundo donax on the Rio Grande.Subtropical Agriculture and Environments 70: 11-16.ttp://www.subplantsci.org/wp-content/uploads/2019/09/SAES-Goolsby-et-al.-2019-3.pdf

Goolsby, J.A., C.R. Hathcock, A.T. Vacek, R.R. Kariyat, P.J. Moran, and M. Martinez Jimenez.2020. No evidence of non-target use of native or economic grasses and broadleaf plants by Arundo donax biological control agents.Biocontrol Science and Technology 30: 795-805.

Goolsby, J.A., P.J. Moran, J.A. Adamczyk, A.A. Kirk, W.A. Jones, M.A. Marcos, and E. Cortés. 2009a. Host range of the European, rhizome-stem feeding scale Rhizaspidiotus donacis (Leonardi) (Hemiptera: Diaspididae), a candidate biological control agent for giant reed, Arundo donax L. (Poales: Poaceae) in North America. Biocontrol Science and Technology 19: 899-918. doi: 10.1080/09583150903189099

Goolsby, J.A., P.J. Moran, A.E. Racelis, K.R. Summy, M.M. Jimenez, R.D. Lacewell, A. Perez de Leon , and A.A. Kirk. 2016. Impact of the biological control agent, Tetramesa romana (Hymenoptera: Eurytomidae) on Arundo donax (Poaceae: Arundinoideae) along the Rio Grande River in Texas. Biocon. Science and Technology 26: 47-60. doi: 10.1080/09583157.2015.1074980.

Goolsby, J.A., A.T. Vacek, C. Salinas, A. Racelis, P.J. Moran, and A.A. Kirk. 2017. Host range of the European leaf sheath mining midge, Lasiopteradonacis Coutin (Diptera: Cecidomyiidae), a biological control of giant reed,Arundodonax L., Biocontrol Science and Technology 27: 781-795. doi: 10.1080/09583157.2017.1342222

Marshall, M., J.A. Goolsby, A.T. Vacek, P.J. Moran, A.A. Kirk, E. Cortes Mendoza, M. Cristofaro, A. Bownes, A. Mastoras, J. Kashefi, A. Chaskopoulou, L. Smith, B. Goldsmith, and A.E. Racelis. 2018. Comparison ofTetramesa romana densities across its native range in Mediterranean Europe and introduced ranges in North America and Africa. Biocontrol Scienc and Technology 28: 772-785. doi: 10.1080/09583157.2018.1493090

Moran, P.J. and J.A. Goolsby. 2009. Biology of the galling wasp Tetramesa romana, a biological control agent of giant reed. Biological Control 49: 169-179.doi:10.1016/j.biocontrol.2009.01.017

Moran, P.J. and J.A. Goolsby. 2010. Biology of the armored scale Rhizaspidiotus donacis (Hemiptera: Diaspididae), a candidate agent for biological control of giant reed. Annals of the Entomological Society of America. 103: 252-263. doi: 10.1603/AN09124

Moran, P.J., A.T. Vacek, A.E. Racelis, P.D. Pratt, and J.A. Goolsby. 2017. Impact of the arundo wasp, Tetramesa romana (Hymenoptera: Eurytomidae) on biomass of the invasive weed, Arundo donax (Poaceae: Arundinoideae) and on revegetation of riparian habitat along the Rio Grande in Texas. Biocon. Sci. Technol. 27:96-114. doi: 10.1080/09583157.2016.1258453

Contributing Authors

Dr. Patrick J. Moran, Research Entomologist, USDA