Areawide Release, Evaluation and Implementation of New Biological Control Agents for Control of Water Hyacinth and Arundo
Dr. Patrick Moran, Research Entomologist, USDA-ARS Exotic and Invasive Weeds Research Unit. Patrick.Moran@ars.usda.gov
1. Release the leaf-feeding water hyacinth planthopper for biological control of water hyacinth at up to 30 sites in the Sacramento-San Joaquin Delta and its upstream river watersheds.
2. Release the shoot tip-galling arundo wasp and the root- and shoot-feeding arundo armored scale at up to 15 sites in the Sacramento-San Joaquin Delta and its upstream river watersheds.
3. Verify successful establishment of the biological control agents.
4. Verify that biological control can be integrated with aquatic weed control with herbicides and mechanical removal to reduce the size, reproduction, and spread of water hyacinth and arundo.
Water hyacinth (Eichhornia crassipes), a floating aquatic invasive weed, covers up to 10,000 acres in the Sacramento-San Joaquin Delta, including areas that are inaccessible or impractical for herbicide treatment and mechanical removal. Water hyacinth blocks water flow for pumping intakes, impedes recreational and commercial navigation and creates danger for boats, alters water quality for fish, blocks light for submersed plants and displaces native aquatic plant and animal species.
To implement adaptive, integrated management under the DRAAWP, selection of sites at which specific types of weed control strategies will be emphasized is critical. Selection of sites for water hyacinth biological control is being informed by several sources of information, including:
- Remote sensing of water hyacinth populations using Landsat satellite and airplane-borne systems. DRAAWP project partners from NASA-Ames have developed an automated processing tool to determine acreage of water hyacinth from Landsat images. Analysis of images over the past several years has revealed backwaters, such as flooded islands, where water hyacinth populations persist in spite of nearby control. These sites act as ‘nurseries’ for new populations to develop each year. These ‘backwater nursery’ sites are well-suited for biocontrol, as the stable water hyacinth populations will permit development of large populations of biocontrol agents.
- The detailed knowledge of field operations managers with the Division of Boating and Waterways-California Department of Parks and Recreation, a DRAAWP project partner, who can identify sites at which persistent water hyacinth populations are difficult to control using other methods.
- Information from the San Joaquin and Contra Costa Mosquito and Vector Control Districts, both DRAAWP project partner, who have identified sites, often in non-navigable places and therefore not subject to herbicidal control, at which persistent water hyacinth populations are creating a health hazard by harboring mosquitos.
Arundo (Arundo donax), a giant grass up to 25 ft tall, grows along the edges of sloughs and canals in the Sacramento-San Joaquin Delta, and is also abundant in the Sacramento and San Joaquin River watersheds. Arundo blocks access to water, consumes/wastes water, obstructs flood control channels, creates fire hazards along sloughs and rivers, and displaces native plants.
Site selection for biological control of arundo is being informed by the Sacramento-San Joaquin Delta Conservancy, a DRAAWP project collaborator. The SSJDC has mapped arundo populations in the Delta using both satellite images and ground-level surveys. They have also prioritized sites for integrated chemical-physical-biological control using a restoration prioritization model.
One New Biological Control Agent for Water Hyacinth
As part of the DRAAWP, an integrated, adaptive management plan for water hyacinth is being implemented, including the release and evaluation of a new biological control agent. The USDA-Agricultural Research Service (ARS) in Florida had previously discovered and determined the host range, biology and impact of a planthopper, Megamelus scutellaris, from the South American native range. Releases in California began in 2011 by CDFA, and in 2012 the USDA-ARS Exotic and Invasive Weeds Research Unit in Albany, CA assumed responsibility for field releases. The planthopper adults have both a short-winged form (Figure 1A), which cannot fly but can hop tens of times its small size (less than 1/16th of an inch), and a long-winged form which can fly (Figure 1B). Adult females lay eggs on the undersides of water hyacinth leaf blades and petioles (the stalks supporting the leaves). Eggs hatch in a week or less and complete five immature stages in about a month, then molt to the adult stage. Under warm conditions, the planthopper can build up large populations, over 100 insects per leaf, in just a few months (Figure 1C). Immatures and adults damage water hyacinth leaves by puncturing tissues and feeding on plant juices (Figure 1D), and heavy feeding can kill water hyacinth plants. Field releases are made by placing infested plants into field sites, and up to 20,000 planthoppers are released at each site. Repeated visits by wading or from a boat are needed to evaluate the establishment and impact of the planthopper (Figure 1E). Planthoppers are being mass-reared in six colony cages (Figure 1F), including two at the USDA-ARS in Albany, and four at collaborating agencies on the DRAAWP: two at the Contra Costa Mosquito and Vector Control District in Concord, one at the San Joaquin Mosquito and Vector Control District in Stockton, and one at the California Department of Food and Agriculture in Sacramento. Biocontrol with this planthopper is expected to reduce the ability of plants to reproduce via budding early in the season and reduce the size of mature plants. Both of these effects are expected to make integrated control of water hyacinth easier and less expensive.
Figure 1. Implementation of biological control of water hyacinth using the water hyacinth planthopper Megamelus scutellaris (A-C), damage caused by developing populations on water hyacinth (D), release and evaluation (E), and rearing of planthoppers for additional releases (F).
Photo Credits. A: Seth Johnson/LSU Ag Ctr. B: Mike Ferro/USACE. C: Baldo Villegas/CDFA. D-E: Patrick Moran/USDA-ARS.
Two New Biological Control Agents for Arundo
Two biological control agents were discovered and verified as safe for release in the U.S by the USDA-ARS in Texas. Since 2014, they have been released on populations of arundo in the Sacramento-San Joaquin Delta. Arundo thickets are common on slough levees in the Delta (Figure 2A). The arundo wasp Tetramesa romana (about ¼ inch in length) makes galls in the shoot tips of main and lateral shoots of arundo. Females (Figure 2B) reproduce without mating, and 90% of the population is female. Females live three to five days and can each produce about 25 offspring. The females inject eggs into shoot tips. Eggs hatch after 5-7 days and a gall or ‘tumor’ develops at the shoot tip (Figure 2C). Larvae feed on the gall tissue through three immature stages, pupate, and emerge as new adults within 4 to 6 weeks of egg hatch to repeat the life cycle. At least four generations per year can be produced under warm conditions. Along the Rio Grande in south Texas, five years after release, the arundo wasp has decreased arundo biomass by 20%, by killing lateral shoots and some main shoots, and slowing their growth. So far, the arundo wasp has been released at five sites in the Delta: Big Break; the Sacramento River bank on Andrus Island; and the bank of Middle River on Lower Jones Tract. The arundo armored scale insect Rhizaspidiotus donacis feeds on stems and roots of arundo. Immobile adult females (only 1/16th of an inch across) (Figure 2D, 2E) produce tiny mobile ‘crawlers’ that disperse and settle on shoot buds, then lose their legs and antennae. The scales complete an additional immature stage. Short-lived winged males then emerge and mate with the female scales, which continue to feed and develop the next generation of crawlers. The life cycle takes 4 to 6 months, and two generations per year can be produced in California. At the first release sites in Texas, the scale is reducing new shoot development, and similar impacts are expected in California, where establishment has been confirmed at one site in the Sacramento River Valley (Figure 2F). Releases in the Delta so far have occurred only at Big Break. Many additional releases of both of the arundo agents will occur in 2016. Release technology for the arundo biocontrol agents includes small field cages to increase wasp egg-laying on young shoots (Figure 2G), and release of arundo armored scale crawlers on arundo ‘microplants’, grown from small shoot buds in the greenhouse (Figure 2H). Six months after initiating microplants indoors, they can be taken to field sites and the next generation of crawlers will disperse onto resident arundo plants.
Figure 2. Implementation of biological control of arundo using the arundo wasp Tetramesa romana and the arundo armored scale Rhizaspidiotus donacis. Thickets of arundo along slough levees (A) are being targeted for control. The arundo wasp (B) lays eggs in and galls shoot tips (C). The arundo wasp is established near Big Break in the western Delta. The arundo armored scale forms aggregations on shoot buds and roots (D). Adult females turn from yellow to orange as they mature and develop crawlers (E). The scale is established at one site in the Northern Sacramento Valley (F). Small field cages can be used to increase wasp egg-laying on young arundo shoots (G). Potted ‘microplants’ are infested with arundo armored scales (H), then placed at field sites so the next generation of crawlers can disperse to resident arundo plants.
Photo Credits. A, G, H: Patrick Moran/USDA-ARS. B, E: Crystal Salinas/USDA-ARS. D, F: John Goolsby/USDA-ARS.
Products and Outcomes
1. Three new, widespread, dispersing biological control agents in the Delta targeting water hyacinth and arundo.
2. Reduced ability of water hyacinth to escape control at ‘nursery’ sites in the Delta that are inaccessible to herbicidal or mechanical control.
3. Reduced ability of water hyacinth to rebuild populations in the Delta from upstream plants brought in by water currents.
4. Reduced ability of arundo to occupy and dominate bank levees, floodplains and wetlands in the Delta.
5. Reduced control costs for water hyacinth and arundo.
6. Improved control outcomes for water hyacinth and arundo: increased protection of water resources; improved navigation; clearing of habitats favorable for native plant and animal populations.