Invasive and Exotic Species

Obtaining Purple Loosestrife Biocontrol Agents

Biocontrol insects are obtained either by collecting them (yourself or by a cooperator), rearing them, or purchasing them from a commercial supplier. Consider the following when planning your purple loosestrife biocontrol program:

• Field collecting the biocontrol agents provides robust and healthy insects, and is the preferred method for obtaining the Galerucella species and Nanophyes. If a cooperator is field collecting the insects for you, be sure they collect the agents at the right time of year and under the best conditions, and send you clean, sorted insects as soon as possible. Be sure cooperators know well in advance when you need the biocontrol agents for release.
• Opportunities for collecting the root feeder, Hylobius, are at present limited because it is not widely established in the field and population levels are low where it is established. This weevil is best obtained from cooperators who maintain field insectaries, or purchased from suppliers who rear them.
• Commercial suppliers provide clean, healthy insects. However, purchasing the insects can be expensive. While some suppliers charge as little as $0.10 per beetle, others charge as much as $0.70 per beetle for the Galerucella leaf beetles. Please remember that different prices may also mean different quality and make sure you know under what conditions the insects you purchase were raised or collected. Field-collected beetles are of superior quality when compared to lab-reared individuals, and obtaining adults immediately after they reappear from overwintering will allow you to release individuals with maximum reproductive potential. Nanophyes and Hylobius are even more expensive. Make sure you know the origin of your insects when making purchasing decisions.

3.1 Collecting purple loosestrife biocontrol agents

General Collecting Guidelines

This section provides information on collecting, rearing and purchasing purple loosestrife biocontrol agents with emphasis on the two Galerucella species and Nanophyes. Hylobius is more difficult to collect.

All purple loosestrife beetles insects are most efficiently collected as adults. Planning your collecting activities is important: know how to identify the biocontrol agents, time the collection, prepare equipment and supplies, and train personnel in identification and collection techniques. Follow these general guidelines when planning your collection activities:

Containers. Containers must provide safe environments for the insects while still preventing escape. Use sturdy, breathable containers that allow air flow and will not collect condensation. An example of good containers are pint-sized, nonwaxed ice cream cartons (Figure 25). Plastic containers can also work well if a large hole has been cut in the lid and the hole is covered with mesh or organdy to allow airflow into the container and minimize the buildup of condensation. Glass or metal containers are not suitable.

Figure 25. Non-waxed paper insect containers. (UGA1291025).

To prepare the containers, place cut purple loosestrife stems with leaves loosely in the container, or fit a moist (but not wet) piece of florist foam 1 inch (2.5cm) thick and the diameter of the container snugly at the bottom of each container, and push cut stems with leaves into the florist foam. This provides shelter and food to keep your beetles healthy. Do not put flowers or seeds in the container. Do not put water in the container.

Collecting Methods. Three commonly used methods to collect purple loosestrife biocontrol agents are tap & funnel, sweep net, and aspiration methods. The most appropriate method will depend on the density of the insect population, available time, and available personnel.

Tapping is not selective, so other insects and spiders will be collected along with the biocontrol agents. These insects must be separated from the biocontrol agents before shipping or otherwise transporting the biocontrol agents for release to a new site. Cooling the insects (for example, for 30 minutes in a refrigerator or cooler) before insects are sorted greatly reduces the beetles’ activity, and makes sorting much easier. Use an aspirator (described below) to sort the beetles.

Figure 26. Collecting Galerucella calmariensis before shipping or otherwise from purple loosestrife using the tap-and-funnel method. (Background:transporting the biocontrol agents for release to a new UGA1291026; inset: UGA1291027)

Sweep net. A sweep net is made of a cotton or muslin bag on a hoop, 15 inches (38 cm) in diameter, attached to a handle 3 feet (0.9 m) long (Figure 27). As its name implies, it is generally used to “sweep” adult insects off a plant.

Figure 27. Sweep net for collecting purple loosestrife beetles.

Using a sweep net produces a ‘cleaner’ catch, reducing the need for elaborate sorting. However, sweeping purple loosestrife with a net is difficult and inefficient because woody stems from previous growing seasons interyear’s growth, where insects are active.

• Aspirator: An aspirator is a device used to suck insects from a surface into a collection vial. An aspirator (Figures 28 and 29) is used to collect insects out of a sweep net or off a sorting tray—though it can also be used to take insects directly from the plants. Aspirating is easy and selective, and is the preferred method to sort insects.

A more effective way to use a sweep net is to bend the purple loosestrife flower heads into the net and shake the plants to dislodge adults into the net. This method works especially well for Nanopyhes, and when Galerucella populations are low. The ‘catch’ must still be sorted before placing the biocontrol agents into containers.

Sorting separates the biocontrol agents from unwanted insects, other organisms and debris, such as weed seeds, collected along with the beetles. Empty the contents of the net or collecting container onto a tray and aspirate the purple loosestrife beetles out of the debris. If the collected material is first chilled, the insects will move slower and will be easier to collect biocontrol agents from field insectaries or from open field sites having an abundance of insects. Collect adults at the beginning of their peak emergence times, when female beetles have their maximum oviposition potential, and are most likely to establish thriving populations at the site where they are later released. Emergence (the optimal time for collection) will vary from region to region and year to year. For example, Galerucella can be collected as early as mid-April in warm, western locations, and as late as early June in cooler, eastern locations. You may need to contact your state biocontrol expert, county weed superintendent, or university extension educator to identify the best collection sites and times. Approximate recommended collection times are provided in Table 6.

Figure 28. Aspirator used to collect purple loosestrife beetles.

Figure 29. Galerucella calmariensis collected in aspirators. (UGA1291029)

Specific Collecting Guidelines

Table 6. Methods and timetable for collecting purple loosestrife biocontrol agents.

Wait for a day with good weather. Do not collect in the rain: insects will hide and become difficult to find in rainy weather, and excess moisture causes health problems—beetles may also drown in wet collection containers. The only exception to this rule is the root feeder Hylobius, for which overcast and rainy days are optimal for collecting the generally night-active adults.

Leaf beetles (Galerucella): Adults are easily collected with a funnel or sweep net during the warm part of the day when they are most active. Aspirating is also a suitable, although slower, method for collecting adults. The best time to collect adult beetles is in mid-May to early June, when they have emerged from overwintering sites and are actively feeding, congregating, and mating. The second period of activity occurs from early July to August, when the next generation of adults emerge. Larvae or eggs are not generally collected because of extremely high mortality rates during transportation.

Flower weevil (Nanophyes): Nanophyes adults are easily collected by bending and shaking the developing purple loosestrife inflorescences over a sweep net, dislodging the beetles into the net. Aspirating individual adults or mating pairs from plants is possible but slow and laborious. Collect Nanopyhes during the heat of the day—most appropriate collection times are when inflorescences begin to form but before plants begin to flower—mating pairs congregate at the top of these plants, and are easily seen. Depending on the location of the site, the collecting period is generally about late June to mid-August.

Root weevil (Hylobius): Hylobius is the most difficult of the purple loosestrife biocontrol agents to collect because it is generally nocturnal or only active on rainy or overcast days. Also, population numbers are currently still low, so field collecting is limited. Where it is possible to collect, do so in the early evening or at night with a flashlight. Weevils are most easily collected by locating an adult on a plant, carefully approaching the plant, placing a sweep net under the stem, and allowing the beetle to drop into the net (they quickly drop from the plant when they sense your presence). Adults can also be collected at the base of the plant by removing the leaf litter and handpicking individual beetles, but this activity is very time-consuming, and will only yield good results at high weevil densities. Adults can be collected from late June to late August. (Note: because Hylobius is not widely established at present, it will be necessary to purchase the weevils from rearing operations until field populations have built up sufficiently to allow collection.)

3.2 Rearing purple loosestrife biocontrol agents

Programs to rear purple loosestrife biocontrol agents have focused primarily on the Galerucella leaf beetles because they are relatively simple to rear. Rearing enables large numbers of beetles to be rapidly produced and distributed. In many parts of the United States and Canada, communities, agencies, youth groups, and schools have developed mass rearing programs to help distribute the beetles throughout their states and regions and to provide opportunities for public awareness and education.

You can find many examples of state programs on the internet. For example, the Illinois Natural History Survey (http://www.inhs.uiuc.edu/cee/loosestrife/bcpl.html) manages a very successful rearing program with elementary and high schools. The Vermont Purple Loosestrife Biocontrol Program has hosted a volunteer community rearing program of Galerucella beetles for several years (http://www.anr.state.vt.us/ dec/waterq/wetlands/htm/wl_purpleloosestrife.htm). Other active programs are found in Michigan (http://www.miseagrant.org/pp), and Minnesota (http:// www.seagrant.umn.edu/exotics/purple.html). For additional information about rearing purple loosestrife biocontrol beetles, visit the internet web sites listed in the Selected References section.

General Galerucella Rearing Guidelines

We focus in this guide on rearing the Galerucella leaf beetles. The methods outlined here also work well for Nanophyes, except that adult weevils are introduced when plants begin to form flower buds (by mid-summer). Rearing Hylobius is not recommended because it is comparatively slow and usually requires highly specialized facilities or large numbers of plants.

• Obtain plants: In early spring before plants sprout, dig about 100 mature purple loosestrife roots, each with at least five or six stems. Take the roots to your rearing location and pot them into plastic 4-gallon (3.8 l) pots filled with standard commercial potting mix and a slow-release fertilizer. Place up to 12 pots in a plastic wading pool about 6 feet (2 m) in diameter. Fill the pool with 4 inches of water to simulate a wetland environment (Figure 30). Check the water daily and refill as needed throughout the growing period. If wading pools of the proper size aren’t available, construct a pool using pond liner or thick plastic sheeting that can hold water to keep plants moist and healthy.
• Cover plants: Place a 4- to 5-foot (1.2 – 1.5 m) tall tomato cage over the pot (if you intend to rear Nanophyes, these cages will need to be taller, to allow the plants room to develop inflorescences), and cover the cages with fine mesh netting (no-see-um netting works well). Secure the top and bottom of the netting with twine, tape or heavy rubber bands: this will keep the beetles in the cage and prevent entry of aphids or other pests and predators that might interfere with plant or beetle growth.

Introduce beetles: When plants are about 1 foot (30cm) tall, place 10 to 15 beetles in each cage (use only plants that produce an abun- dance of healthy shoots). Be sure to put only one beetle species in each cage. If you rear Nanophyes, place six to ten individuals in each cage. Adults will feed for a few days then begin mating and laying eggs. Galerucella, while small at first, will be obvious in a few weeks.

Figure 30. Wading pools used to grow purple loosestrife and to rear Galerucella calmariensis.(UGA1291030)

Development (from egg to adult) takes approximately 30-40 days, and new adult beetles will begin to appear and congregate near the top of the plants. Nanophyes larvae will be concealed inside the bud. Each large plant yields between 500 and 2,000 Galerucella beetles or 300 Nanophyes adults. Make sure the newly-emerged adult beetles have sufficient foliage to feed.
• Transport beetles after rearing: Transport the newly reared beetles in the covered, potted plants to the release site and place them next to healthy, wild purple loosestrife plants. Remove the net bag and the wire cage; gently shake the net bag to dislodge any beetles remaining in the bag. Remove the plant from the pot and rest it on the ground in the infestation; this allows the beetles to disperse on their own. Record the location of the site, the weather conditions at the time of release and, if possible, record the GPS coordinates or legal description of the release site. Use the Purple Loosestrife Biocontrol Release Form to record the release.
• Overwintering potted plants and beetles: It is quite easy to overwinter beetles outdoors to have a large supply for the next year. Retain a portion of the reared beetles on large, caged plants removed from the wading pool. Make sure they have sufficient high-quality food; beetles will feed for a while and disappear into the duff at the base of the plant, where they will remain until spring. To maximize plant and beetle survival, thoroughly mulch and shade the plants throughout the fall and winter. Other elaborate and specialized rearing programs use large cages (Figure 31) or greenhouses (Figure 32) to mass-produce adult beetles, but such programs are expensive and labor-intensive.

Figure 31. Large mesh cages of potted purple loosestrife for rearing biocontrol agents. (UGA1291031)

Figure 32. Mesh-covered purple loosestrife plants in a greenhouse used to rear biocontrol agents. (UGA1291032)

Rearing Hylobius on semi-artificial diet

An alternative mass rearing method using a semi-artificial diet has been developed for Hylobius. While not widely used in weed biocontrol, rearing insects on artificial diet is a well-established practice in agricultural pest management. The semi-artificial diet, which has the consistency of stiff jelly, is comprised of multiple ingredients, but most importantly contains ground purple loosestrife roots. Root weevil larvae are reared individually on diet in small containers. They complete development in three months instead of one-to-two years under natural conditions in the field.

Advantages of artificial diet:

• Development time is reduced from one-to-two years to three months
• Eliminates slow, tedious field collection
• Large numbers of beetles can be reared
• Enables year-round beetle rearing

Disadvantages of artificial diet:

• Expense
• Requires specialized equipment and skill

See the article by Blossey et al. (2000), cited in the Selected References section, for information on use of a semi-artificial diet to rear Hylobius.

3.3 Purchasing purple loosestrife biocontrol agents

When purchasing biocontrol agents from a commercial supplier or when obtaining insects from a cooperator, it is important to ensure that the insects are healthy and received in good condition. It is also important to obtain the biocontrol agents at the correct time of year. Be sure also to have the correct permits for interstate transportation of insects. For more information or to find a commercial supplier, contact your cooperative weed management area, your county weed control superintendent, or your state biocontrol of weeds expert.

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