Technical Service Center
Environmental Applications and Research Group — Publications
Purple Loosestrife Biocontrol Research Program at the Bureau of Reclamation Technical Service Center
Technical Memorandum No. 8220-96-13
Summary of 1995 Activities
The Bureau of Reclamation (Reclamation) constructs and manages water storage and delivery systems in the 17 Western states. Purple loosestrife is a serious problem in some of these states, a newcomer to others, and still unidentified in a few. In areas where it is found, it rapidly impedes Reclamation water systems and degrades associated wetland habitats. The Technical Service Center (TSC) provides assistance with loosestrife identification and control to Reclamation facilities.
Initial Reclamation field research on biological control of purple loosestrife began at three Denver-area sites in 1994. Adults of Galerucella calmariensis and G. pusilla (leaf-feeders) were released at all three Denver-area sites, and eggs of Hylobius transversovittatus (a rootfeeder) were inoculated onto plants at Coot Lake in Boulder, and the Federal Correctional Institute (FCI) in Englewood; no Hylobius were inoculated at Ward Lake. Insect breeding for these releases was conducted at the Denver Federal Center, with some Galerucella provided by the Colorado State Insectary. Details on 1994 activities can be found in the Summary of 1994 Activities, Bureau of Reclamation Technical Memorandum No. 8220-95-1.
Galerucella: Leaf-feeding beetles
The establishment of a biocontrol insect species can be affected by many factors, probably the most significant of which is the weather. The winter of 1994-1995 was not especially harsh or cold (lowest average minimum temperature was 21' F, see Appendix 2), which probably helped the overwintering success of the Galerucella in the field. Exceptionally heavy rains and cool temperatures into June may have delayed their reproduction, but did not seem to have any significant effects.
The first search to determine the success or failure of field-overwintered Galerucella was conducted on May 30, 1995. On this date, the emerging perennial loosestrife plants at FCI and Coot Lake were 6-8 inches tall, while the loosestrife at Ward Lake was 24 inches tall. No insects or feeding damage were seen at FCI or Ward Lake, but adult Galerucella and feeding damage were found at Coot Lake within one of the original release sites. Eggs were found on June 7 at Coot Lake, June 14 at Ward Lake, and June 21 at FCI, at areas in or near the initial release sites. Widespread larvae and larval feeding on plant apices were noted at Coot Lake on June 23. Some of these were found between 50-100 meters from the original release sites.
Additional releases of mixed species of Galerucella adults (G. calmariensis and G. pusilla) were made at all sites: 326 were released at Ward Lake, 546 at FCI, and 250 at Coot Lake. A new field site was added to the purple loosestrife biocontrol efforts in August when 3252 adults were released (using cages) near Ephrata, Washington on Reclamation's property at the Columbia Basin Project, Winchester Wasteway. This site will be developed as a Reclamation biocontrol demonstration project using information learned at the Denver-area sites.
Few problems were encountered in rearing Galerucella in the greenhouse this year. There was 75% survival from adults overwintered in the growth chambers, and no aphid infestations occurred on the plants being used for insect rearing. From data collected during the year we found that the peak emergence of new adults occurred during the two-week period beginning about 43 days after the parental adults were put on plants to breed. This is useful information for future planning of workload schedules and release dates.
Hylobius: A root-feeding weevil
In January 1995, greenhouse plants whose roots had been inoculated with Hylobius eggs in 1994 were cut back, freed from the soil and washed, then packed in damp sphagnum in environmental growth chambers. In July, new adults began emerging from these roots. Fifteen percent of the eggs from these 1994 greenhouse inoculations have emerged as adults, this percentage will increase as more adults emerge in 1996. Roots stored in the growth chambers that were inoculated using the original 1993 shipment of eggs were checked for remaining larvae. When none were found, the roots were discarded.
The Hylobius adults that overwintered (1994-1995) in the growth chambers did well; only one of the 17 adults died. After the addition of the new adults noted above, the current stock of Hylobius adults is 67. No adults were released into the field in 1995.
Total egg production was less than in 1994, with 546 eggs produced. Of these, 80 were sent to the Tennessee Valley Authority, 132 were inoculated onto greenhouse plants, and 334 were inoculated into field sites: 200 at Coot Lake, 77 at Ward Lake, and 57 at FCI. Eggs were inoculated directly onto greenhouse roots, but some field-inoculations were done using a new technique of inoculating the eggs vertically into a cut stem. Subsequent evaluation of these vertical inoculations showed that only about 25 percent of these larvae survived and tunneled all the way to the roots.
Nanophyes: Seed-destroying weevils
The genus Nanophyes will complete the introduction of insects for the biocontrol of purple loosestrife. Two species, N. brevis and N. marmoratus, will eventually be introduced. The importation of N. brevis has been delayed because insects collected in Europe were infested with a parasite. However, all specimens of N. marmoratus were clean and able to enter the United States.
Nanopyhes adults are very small, about the size of the head of a pin, and cause minor feeding damage on loosestrife leaves. Females lay one egg in each flower of Lythrum salicaria, which develops into a larva that affects the seed production of the flower. N. marmoratus larvae feed on the unopened, unpollinated flowers and ovules, while N. brevis larvae feed on the later stages of the flower and seeds. The time from egg to adult is about one month. The adults overwinter in the leaf litter and complete their one-year lifespan after laying eggs the following summer. On September 30, we received about 730 N. marmoratus from Dr. Bernd Blossey of Cornell University. Three hundred of these were released into the leaf litter at the FCI site, and the remainder were overwintered in the growth chambers for greenhouse culture in 1996.
The three Denver-area sites were aerially photographed in August and October, and the Washington site in September and October. We plan to make some flights next year when the flowers are closer to peak bloom.
Ground surveys were conducted in the Denver-area sites in June (to determine plant densities along permanent survey lines) and August (to measure inflorescence length and plant height in a random sample of 100 of the largest plants). The densities showed much variation between samples, but following the same survey lines from year to year should show any developing trends. Data on plant height and inflorescence length respectively showed the following values (cm): Coot Lake: 184.6 ± 27.4, 24.88 ± 7.63, FCI: 184.6 ± 27.4, 24.88 ± 7.63, Ward Lake: 199.15 ± 17.31, 51.45 ± 14.48. The longest inflorescesce length (center flower spike) was found at Ward Lake and measured 87 cm. Reference samples of flower spikes were collected at all locations as baseline data before Nanophyes introductions.
The installation of a new computer-controlled greenhouse system was completed in late spring. This system should provide better environmental control, along with data on daily greenhouse temperature and lighting conditions. The installation caused some delays in 1995 Galerucella breeding efforts, but there should be no further delays next season.
Dr. Bernd Blossey of Cornell University visited Denver in September to deliver Nanophyes adults and to evaluate our facilities and suggest methods of maximizing our insect production. Many of our staff and cooperators attended his seminar about biological control of purple loosestrife. Dr. Blossey has invited us to help develop a set of national standards to monitor the effectiveness of purple loosestrife biocontrol. Many of the future plans in the following section were based on discussions that took place during his visit, and on his written review of our program.
Searches for successfully-overwintered adults will begin earlier in the season so a definite time of emergence can be pinpointed. Many weather-related factors could influence the emergence date from year to year. An effort will be made to tie insect emergence after winter with other field events (eg., the blooming of a certain species of flower) that might be used as a marker.
Based on recommendations made by Dr. Blossey, some of our procedures will be changed to increase our insect production. In 1996, we will raise Galerucella on field-dug, potted and sleeved plants placed in a lined pond by the greenhouse. (Since these plants must be very large, we will use plants grown from large, field-dug roots, and not rely on plants started from cuttings.) These roots were dug in October with the assistance of personnel from FCI, and potted in Reclamation's greenhouse over the winter. To reduce time spent transferring breeding adults, each plant will receive only 10- 15 adults, and collection of the newly-emerged insects will be facilitated by using sleeves designed with a one-way funnel trap.
Populations of Galerucella seemed to be establishing at all three Denver-area sites, so no large releases are planned. However, if insects fail to overwinter at any site, more will be released. Most of the Galerucella produced in 1996 will be used to establish a large, viable population in the Winchester Wasteway, Washington. With several thousand acres of solid loosestrife, this site can easily absorb many insects. Galerucella will be released at discrete "islands" of one to five acres of loosestrife within this "sea" so that any effects can be noticed more quickly.
We currently have one of the largest laboratory breeding stocks of Hylobius in the world, at 67 adults. Some of these adults will be redistributed among other researchers, and it is not anticipated that any of the adults will be released into the field in 1996. Egg production should increase and inoculation of eggs into field plants will become a major activity.
Evaluation of various inoculation techniques will continue. We will repeat testing the inoculation of eggs vertically into cut stems, especially at sites like Ward Lake where the soil is too dry to inoculate directly onto the roots. We will continue to monitor this type of inoculation for presence of a possible parasitic wasp, a general parasite that can prey on Hylobius larvae. At Coot Lake, where the soil conditions are wetter, we will inoculate the eggs primarily onto the roots. Inoculation of eggs onto plants at the Winchester Wasteway site will be limited by the perishablilty of the eggs, and the number of trips that can be made to the site.
Hylobius adults are reclusive and are active at night and on cloudy days. They are very difficult to find, so evaluations of their presence will rely mostly on observations of the plants for feeding and ovipositing damage.
If Nanophyes released at FCI do not overwinter successfully, another release will be made in the spring from our laboratory stock. Little is known about raising Nanophyes in a laboratory or greenhouse setting, so we will be working with other researchers to develop these methods. If we are successful, additional releases will be made at FCI.
We do not plan to release Nanophyes in areas where the land managers prefer to eliminate all seed sources until we can release enough insects to decrease seed production to the point where cutting flower spikes will not be necessary. This is necessary because the life cycle of the insect is not compatible with the cutting of flower spikes. Further, as populations of Galerucella increase, there will be a decrease in the number of flowers and seeds produced. The remainder of seed production can then be controlled with Nanophyes alone.
At the beginning of the 1995 field season, no national standards for monitoring the effectiveness of biological control for purple loosestrife had been established. This has been of concern, as researchers wish to draw together all the data gathered for North America and present one of the first, well-documented studies of the process of biological control of an exotic plant species. Preliminary monitoring criteria have now been established and will be tested by us and several other cooperators. These will be reviewed and finalized in a meeting in October 1996.
We will continue to use permanent 1 m2 quadrats established in 1995. These quadrats are randomized and cover areas with and without loosestrife plants. This design should enable the documentation of a potential spread or changes in density or species composition in the established loosestrife stands.
Monitoring will take place at least three times a year, initially four weeks after adults become active in the spring (generally mid June), in mid August, and after senescence of purple loosestrife. Measurements will include three groups of data: a) for plants: abundance of species and stems, height, per cent cover, phenology, length of inflorescence, b) for insects: abundance of adults and larvae, damage level, and c) some general information about the weather, time of day, and investigators.
Aerial photography will continue, resulting in the development of maps showing the extent of the loosestrife infestations. We also plan to use GPS (Global Positioning System) and GIS (Geographic Information System) technologies to help delineate both loosestrife infestations and insect populations.
We would like to express our appreciation for the contributions and support from the following:
Bureau of Reclamation Research Program WATER Project EE007
"Development of Improved Aquatic Pest Management Methods"
Bureau of Reclamation Program Analysis Office
Cooperators Dr. Bernd Blossey, Cornell University
City of Boulder, Colorado, Division of Mountain Parks
U.S. Dept. of justice, Federal Correctional Institution, Englewood, Colorado
Ward Lake Tree Company
Bureau of Reclamation Pacific Northwest Region and the Ephrata Field Office
City of Boulder, Colorado, Open Space
Jefferson County, Colorado, Open Space
Colorado Division of Wildlife
Colorado Department of Agriculture, Division of Plant Industry