Linda M. Wilson, Cynthia Jette, John Connett, Joseph P. McCaffrey. 2003. Biology and Biological Control of Yellow Starthistle. USDA Forest Service FHTET-1998-17 2nd Ed.

Chapter 3: Elements of a Yellow Starthistle Biological Control Program

This chapter discusses the elements necessary to successfully establish and operate a yellow starthistle biological control program. Successful biological control programs require careful planning and implementation and a commitment to evaluation and monitoring. This chapter provides detailed information and guidelines to make your yellow starthistle biocontrol program a success.

Figure 28. Yellow starthistle plant (UGA1350037).

1. Background information. Read the information contained in this manual and become familiar with: 1) general knowledge of biological control of weeds, 2) yellow starthistle biology, and 3) its biocontrol agents (also referred to as bioagents, flies, and beetles). It is essential to be able to identify yellow starthistle (Fig. 28) by growth stage, each of the biocontrol agents, and to recognize how they impact the weed.
   
   
2. Select the release site. Make note of the bioagents already present at the selected site (see "Selecting a Site").
   
   
3. Schedule field activities. Timing of the collection and release is crucial for the success of a biocontrol program; thus, pay close attention to scheduling of field activities. For optimum results, follow the timetables suggested in this chapter as closely as possible.
   
   
4. Obtain bioagents. Collect, handle, transport and release the bioagents at the selected site.
   
   
5. Monitor bioagents and vegetation.

A systematic process to establish a yellow starthistle biological control program consists of the following elements:

1. Selecting and preparing study sites
2. Collecting biocontrol agents
3. Transporting biocontrol agents
4. Releasing biocontrol agents
5. Monitoring
1. Biocontrol agents
2. Vegetation (quantitative and qualitative)
6. Establishing photo points

Methods for carrying out each of these processes are discussed in separate sections in this chapter.

(For solutions to common problems encountered when establishing a starthistle biocontrol program, see Appendix A.)

1. Selecting and Preparing Release Sites

There are three types of biocontrol sites: study, nursery, and field release.

Study site. A study site is a release site where the damage and impact is evaluated. Study sites can be used as demonstration areas for educational and training purposes, and can be monitored intensively to determine the effects of bioagents on starthistle over time. However, demonstration and monitoring activities at the study site should be planned carefully because frequent site visits can damage the site through disturbance and trampling of vegetation.

Nursery site. A nursery site, or field insectary, is used to grow large quantities of surplus bioagents for redistribution to other starthistle infested areas where bioagents have not been previously released or are of low density. Nursery sites should be left undisturbed for 3 to 5 years to allow the bioagent populations to increase. Careful monitoring will determine when the bioagent population is large enough to enable collection for redistribution. It is essential that nursery sites receive minimal disturbance.

Field Release. A field release site is simply an open site for general control purposes. Monitoring or redistribution efforts are not planned for these sites.

Selecting the Site

The type of site you select will depend on the objectives of your biocontrol program. Visit prospective field sites. Use the following guidelines and criteria to select a site (study, nursery, or field release).

Location. Consider accessibility, slope and cover (avoid shaded, forested sites).

Size of site. An area with at least 2 acres of starthistle infestation is minimal. However, a larger area of infestation is more desirable (Fig. 29). Presence of bioagents. If bioagents you want to release are already present at the prospective site, move on and choose a different location. Density of infestation. Choose a moderately dense area of infestation, an area containing three or more

Figure 29. Example of yellow starthistle infestation suitable for a biological control program (UGA1350038).

Landuse and disturbance factors. Select sites that are not cultivated, away from land development, and where no livestock are grazed.

Pesticides. Select sites which are pesticide-free (no herbicides and insecticides have been or will be applied to the area).

Landowner consent. The landowner/manager must be willing to have the release site available for visitations and monitoring over several to many years. Consent is particularly important when planning a study or nursery site. When getting permission to use a site, be sure to secure the following:

1. Written permission from the landowner or land manager allowing use of the area as a release site.
   
   
2. Written agreement by the landowner allowing access to the site for monitoring and collection for a period of at least 6 years (3 years for establishment and buildup and at least 3 years for collections).
   
   
3. Permission to put a permanent location marker at the site.

Preparing the Site

Preparing the release site involves the following activities:

• Determine the need. Look for presence of bioagents before the release is made. Some yellow starthistle bioagents are so common and widespread that it is no longer necessary to redistribute them. For example, the weevil Bangasternus orientalis is the most widespread agent and will likely already be present at the site. If so, it will not be necessary to release this weevil at the site.
  
  
• Establish a permanent location marker. After selecting a site, choose a dense, uniform patch of yellow starthistle in which to place a marker. Use white-colored markers (wood or metal stake) to mark the exact location of the release. The stake must be tall (about 4 feet [1.2 m]) and clearly visible so that it can be easily found during future visits.
  
  
• Set up a photo point. A photo point (see page 47) is used to photographically record changes in yellow starthistle infestation (decline or increase) over time following release of bioagents at a site. Use a permanent feature in the background as a reference point.
  
  
• Draw a map. A map and written directions to study and nursery sites are essential for other people to locate the site. Note permanent roads, creeks, rivers, mile markers, etc. Include the legal description or latitude and longitude global positioning system (GPS) coordinates so that the site can be easily re-located.
  
  
• Monitor baseline vegetation. In study sites where vegetation will be monitored, baseline data are used for comparing yellow starthistle infestation measurements before and after releasing bioagents in the area. It is always useful to collect baseline vegetation data even at nursery or field release sites (see page 44).

2. Collecting Biocontrol Agents

Planning and timing of the collection is critical (Chart 1). The type of bioagent will dictate the best time in the season and method of collection. Ensure that all necessary collection supplies are on hand. Also, accurate identification the bioagents is important. Whether collecting larvae or adults, follow these general guidelines.

Chart 1. Phenology of yellow starthistle and its biocontrol agents.

General Collection Guidelines

Quantity. The minimum needed to optimize establishment is 200 bioagents per site, but more is better.

Containers. Use "breathable" containers at all times. Breathable containers allow air flow to the insects and will not form condensation. One of the best containers to use is a pint-sized, non-waxed ice cream carton. These are sturdy and breathable. Paper bags can work as temporary containers if care is taken to keep the bag from getting wet or squashed. Do not use plastic bags as containers because they are airtight and will not release moisture. Put a small wad of toilet tissue in the container to absorb moisture and to give the insects a crawling surface.

DO NOT USE PLASTIC BAGS AS CONTAINERS

Cooling. Keep bioagents shaded and cool at all times while collecting, sorting, counting and transporting. Bring a cooler with pre-frozen blue ice packs to the field. Secure an ice pack to the interior side of the cooler so that it does not roll around and crush the bioagents.

KEEP INSECTS COOL AND SHADED WHILE COLLECTING

SORTING, COUNTING OR TRANSPORTING THEM

Planning and Timing

Planning and timing of bioagent collection is critical. It involves knowing where, when, how and what to collect.

Where to collect

Collect from nursery sites or open field sites that have an abundance of insects. You may wish to consult with your county extension educator, university or state entomologist, or county weed superintendent for an appropriate site.

How to collect

Choose a collection method suggested in Table 6 (page 35). The best collection method is the one that i) produces the greatest number of insects in the least amount of time and effort, ii) produces insects in the best condition, and iii) requires to least handling and sorting (clean collection). The six typical collection methods are as follows: sweep net, aspirator, handpicking, tapping (stick and bucket), black light, and seedhead collecting.

Table 6. Collection methods for yellow starthistle biocontrol agents.

Table 7. Release methods for yellow starthistle biocontrol agents.

Figure 30. Sweep net.		Figure 31. Sweeping for insects (UGA1350070).
Figure 32. Aspirators for collecting biocontrol agents. a. Manual.
		Figure 32. Aspirators for collecting biocontrol agents. b. Hand held vacuum, gasoline or battery powered.

• Sweep net: A sweep net is made of cotton or muslin on a 10"-15" hoop attached to a 3’ (0.9 m) long handle (Fig. 30). As its name implies, it is used to "sweep" weevils off the yellow starthistle. The sweep net method is relatively easy and efficient and is recommended for collecting adult weevils. It is best to sweep no more 25 times and then aspirate the insects out of the net, alternating between sweeping and aspirating (Fig. 31). This reduces the harm that could result from knocking the bioagents around with debris or other insects inside the net.
  
  
• Aspirator: Use an aspirator (Fig. 32) to suck the weevils from the plant or out of a sweep net. When using an aspirator, little unwanted or unknown material is inadvertently collected and the quantity of the agent being collected is easier to record. Transfer the weevils form the aspirator to a collection container. Seal and label the cartoon whith the species, number of bioagents, collection site and date.
  
  
• Tapping: If a sweep net is not available, tapping is the easiest collection method to use for collecting weevils. Using a stick, gently tap the yellow starthistle stems to knock the weevils into a bucket or onto a plastic tray. Separate the weevils further from unwanted plant material that dislodges during tapping, then place them in a breathable container.

What to Collect

For starthistle biocontrol agents, weevils are collected as adults and flies are collected as larvae or pupae. See Table 6 for the appropriate life stage in which to collect bioagents.

Collecting weevils. Weevils are best collected as adults. The ideal weather for collecting weevils is a sunny, warm day with a slight breeze. It is best to collect weevils when they are mating to ensure you are collecting both males and females and that eggs will be laid at teh new site (Fig. 33). Adult weevils can be collected easily by sweep-netting. Hand-picking is possible but it is slow. Weevils will usually jump away or fall to the ground when they see you coming.

Figure 33. Collecting yellow starthistle biocontrol agents (UGA1350039).

Collecting flies. Flies are best collected as larvae or pupae. Sweeping adult flies is not recommended because they are fragile and can be damaged during collection, transportation and release. Rather, collect fly-infested heads in late winter or early spring (mid-February to mid-March). Flies are overwintering as larvae or pupae in the heads at this time. Heads can be taken indoors to rear out adults, or taken to the new site and left to emerge as adults under natural conditions.

Rearing flies indoors

Collect several hundred dry seedheads from last year’s plants and put them in labeled paper bags. Once indoors, adults will likely emerge in a few weeks, so time the collection of heads carefully. You do not want adults to emerge too early and be out of synchrony with the starthistle plants, so collect heads a few weeks before flies would normally emerge outdoors. Empty infested seedheads from bag into a clear, breathable container such as a covered

Figure 34. Insect rearing cage, also called a sleeve box.

3.  Handling Biocontrol Agents

How the bioagents are handled after collection and transported to the release site can affect whether the bioagents will survive and multiply at the new site. This section contains guidelines for transporting and shipping the bioagents.

Transporting Bioagents

How the bioagents are handled and transported can greatly impact whether they become established. It is best to redistribute the bioagents immediately after they are collected to prevent injury to the specimens, within 24 hours if possible.

For later redistribution. Store the weevils in a refrigerator. Weevils can last up to 3 days in a refrigerator; however, only 1 day of refrigerated storage is recommended. For storage longer than 1 day, bring them out of the refrigerator for an hour each day. Seal and label the container. Seal with tape and label the container with the name of the bioagent, the quantity collected, and collection date. Tape a blue ice pack to the bottom of the cooler to avoid physical damage. Put a barrier (e.g., newspaper) between the ice pack and the bioagents to protect the bioagents from excess moisture or cold.

Figure 35. Paper-towel lined carton containing bioagents (UGA1350071).

Shipping Bioagents

To ship bioagents over a long distance, plan the route and timing of shipments to prevent undue delays and stress on the bioagents. Ship the agents by overnight courier and notify your cooperator when they are being shipped, when they can expect to receive them and to release the insects immediately. Try to collect on the Sunday or Monday, and ship Tuesday or Wednesday, so releases can be made before the weekend. Avoid shipping late in the week, and be aware of holidays etc, that can delay shipping. Overall, observe the following guidelines:

Shipping containers. Put bioagents in containers with enough space to allow the insects to move about within the container. Line the container with a crawling surface for the insects (such as wadded tissue or paper towel). Do not put food or water in the container. Tape lids on the containers and make sure that the bioagents do not get caught on the sticky part of the tape. Pack the shipping container with care. Tape the blue ice packs to the inner side of the chest and pack with a layer of paper to absorb condensation (Fig. 36). Keep the bioagents cool until they are shipped.

Figure 36. Shipping box containing agents and cartons, styrofoam to prevent shifting, and blue ice packs (UGA1350072).

Summary: Care of Bioagents

• Provide the bioagents with a crawling surface, such as crumpled tissue or paper towel.
  
  
• Avoid physical damage to the bioagent by taping down potentially harmful objects, such as blue ice packs.
  
  
• Ensure that predators (i.e. spiders and ants) are not trapped with the bioagent in the container by sorting bioagents before packaging them.
  
  
• Do not expose bioagents to heat above 80°F. Keep shipping containers cool (in a cooler) and out of direct sunlight.
  
  
• If release or shipping is not immediate, store the bioagents in refrigerators no colder than 40º to 50º F (4ºC) for a no longer than 2 days or keep them in an ice chest until the bioagents are ready to be shipped or transported. Longer storage decreases the bioagents’ chance for survival at the new site.
  
  
• Provide container with adequate ventilation. If necessary, punch holes in the lid with a pin.

4.  Releasing Biocontrol Agents

Timing the bioagent release is critical (see Table 7, page 35). It will determine whether the bioagents survive and flourish at the new site. Follow these steps for releasing bioagents:

1. Place the permanent location marker. Release the insects at the location marker. This location will be later used in monitoring activities.
   
   
2. Make the release. Consult Table 7 to determine the appropriate method to use for releasing each insect.
   
   
3. Take pictures. Take a series of photographs to record the release. A photo point will record the change in the site over time. (For further information, see page 47).
   
   
4. Collect baseline vegetation data. Choose a monitoring method (see Tables 8 and 9). Establish baseline data at the time of the release. Use the same monitoring method every year.
   
   
5. Fill out and submit a release form. Complete the Biocontrol Agent Realease Form (see Appendix B). Submit the form to your county extension educator, university or state department of agriculture. Keep a copy for your records.

Table 8. Suggested timing for monitoring yellow starthistle weevils.

Table 9. Suggested timing for monitoring yellow starthistle flies.

Timing the Release

Release bioagents at the appropriate growth stage of the yellow starthistle (review "Selecting and Preparing a Study Site") or check with your county extension agent or county weed supervisor. If most yellow starthistle buds are beyond the recommended stage, it is too late to release at that site.

Do not wait for good weather. If you must release in the rain, provide shelter for the bioagents until they can disperse on their own. One way to do this is to place a cardboard box on its side, place the container in the box and open the lid. The bioagents will disperse when weather conditions improve.

The three methods of releasing bioagents are as follows:

Open-field release. When releasing adult weevils or flies, place the bioagents on the ground within a radius of 3 feet of the permanent location marker under yellow starthistle plants where they can continue to mate and disperse on their own. Figure 37. Screen cage in which to release yellow starthistle biocontrol agents (UGA1350041).

Figure 38. Milk jug release cage for yellow starthistle bioagents.

Retaining Voucher Specimens

Retain 5 to 10 bioagents (dead or alive). Put the bioagents in a small vial with 70 percent ethyl alcohol (ethanol) or rubbing alcohol for a voucher specimen. On a piece of white paper, in pencil (always use a pencil because alcohol will dissolve and bleed ink from pens and markers), write the name of the bioagent, source of the bioagent, the date of release, person or agency releasing, and release site. Put inside the vial. This identifies the bioagents released for future reference. Save several specimens for in-house records. Send the voucher specimens to your county extension educator or weed biocontrol expert.

Frequency of Release

Generally, if done correctly a single release will be sufficient to establish a bioagent population. More than one release might be needed if a prior release fails. It might take 2 years to determine if the release was successful.

Releasing Multiple Bioagents

It is expected that bioagent populations will overlap and eventually sort themselves out naturally depending on the habitat, population density, and weed levels. As a rule, however, separate the species by at least 110 yards (100 m) to allow your insect to establish without being impeded by another species.

Suggestions for Optimal Establishment

• A release of 200 bioagents is minimal.
  
  
• Releasing in the early morning hours between 6 and 10 a.m. or in the cooler evening hours between 7 and 8 p.m. is recommended. Bioagents are less likely to fly away immediately when released in cool temperatures.
  
  
• Avoid releasing weevils during rainy or very hot weather for optimal establishment. However, sometimes it may be necessary to release in the rain.
  
  
• Releasing weevils at the bottom of a hill may encourage them to follow the phenological stages of the yellow starthistle uphill, which may possibly increase the rate of spread.
  
  
• Common sense and care is a major factor in the survival and establishment of the insects.

5.  Monitoring

Monitoring is an activity that follows changes in the weed population that you are observing or measuring. In biocontrol, it involves monitoring insects and vegetation at the study site. Monitoring is conducted to: 1) ensure that the bioagents have established, 2) determine of the bioagents have spread from the release site, and 3) assess the impact of the bioagents on the target yellow starthistle. Monitoring provides useful information. Consider the Questions to Ask box above to determine your monitoring objectives. Outline your monitoring objectives before you begin monitoring (see Appendix C).

A. Monitoring Biocontrol Agents

When to Begin Monitoring

Some bioagents may be detected as early as 1 year following release. Most bioagents take 2 to 4 years to be detectable. Thus, if no bioagents are detected a year after the release, it does not mean that the insects failed to establish. Revisit the site for 4 years. If no evidence of insects is seen, either choose another site or make additional releases (see Appendix A for reasons on why agents fail to establish.) Consult with your county extension educator or local biocontrol of weeds expert. See Tables 8 and 9 (pages 42 - 43) to determine how and when to monitor starthistle bioagents.

Monitoring Methods

The monitoring method you choose depends on the life stage of the insect, amount of time available, expertise of the observer, availability of equipment, and your monitoring objective.

For example, to merely determine if bioagents are established at the release site, observing any life stage is adequate. To determine the density of insects at the release site (i.e., number of insects per square yard), more detailed and intensive monitoring is needed. Likewise, if you want to know how far the bioagents have spread from the release site, a more systematic monitoring method is needed.

It is usually necessary to collect bioagents in order to monitor their population and activity. The collection methods described in "Collecting Biocontrol Agents" work just as well in monitoring starthistle biocontrol agents. An additional monitoring method is visual counting adults (Fig. 39). This is an easy and fast way to monitor starthistle insects. Using six to ten, 60-foot (20 m) long transects radiating away from the permanent location marker at the release site, count the number of adult insects you see on or near the

Figure 39. Monitoring yellow starthistl biocontrol agents (UGA1350042).

In order to evaluate larval feeding damage inside the starthistle head, follow this quick method of collecting plants to evaluate larval feeding damage. Collect 10 plants along each of four lines (transects) in four cardinal directions (N, S, E, W) from the permanent location marker, for a total of 24 plants. Clip all of the heads and place them in a paper bag. Label collection bags with site name, date and transect. Heads can be dissected indoors to see if they contain bioagent larvae or pupae. Dissect each bud carefully to determine what larva, pupae and adults is/are in the head (Table 10, page 44). Record the species of insect and the number of larvae present. More than one species can be present in the same head. Be sure to count and record the total number of buds and seedheads collected from each plant.

Table 10. Identification of yellow starthistle biocontrol agent larvae and pupae.

Fill out the "Biocontrol Monitoring Report" (Appendix D).

B. Monitoring Vegetation

Vegetation monitoring is conducted to describe and measure changes in the yellow starthistle population following the release of bioagents. It consists of taking multiple measurements of a variable, such as plant height, density or number of seedheads. Analysis is performed to determine if changes in the weed infestation have occurred. The type of vegetation monitoring to use depends on the type of site (e.g., study or nursery site), availability of resources, and your monitoring objective.

Monitoring can be as simple as before-and-after photos, or counting seeds left in seedheads, or as intensive as conducting field studies for accurate and detailed assessment over time. The level of intensity used in monitoring should be dictated by the questions you want to address and the level of precision you need in the answer. In general, the simpler the monitoring method, the greater the likelihood of obtaining consistent and useful information. Develop a plan for collecting data based on the monitoring objectives. Use the "Monitoring Plan Questionnaire" (see Appendix C) to determine the objective or purpose of monitoring.

Two types of monitoring are qualitative and quantitative.

Qualitative monitoring

Qualitative monitoring uses descriptive elements about yellow starthistle at the management site. It includes such general recording of presence or absence of bioagents, estimates of density, age and distribution classes, infestation mapping, and permanent photo points. Qualitative monitoring tends to be quick and inexpensive, and provides some insight into the status or change of the starthistle population. Its descriptive nature does not allow for detailed statistical analysis. Data obtained in qualitative monitoring may trigger more intensive monitoring later on. In addition, interpretations derived from this type of monitoring are often subjective.

Quantitative monitoring

The purpose of quantitative monitoring is to record and measure changes in the yellow starthistle population after release of the bioagents. Quantitative monitoring can be as simple as counting the number of flowering starthistle plants in an area, or as detailed as measuring plant height (Fig. 40), seed production, rosette diameter and density, biomass, or plant community diversity. The data can be statistically analyzed and generally give precise information on population or community changes. In quantitative monitoring, sampling is more detailed than in qualitative monitoring (e.g., plant height, rosette diameter, number and size of seedheads, percent cover, species diversity). Quantitative monitoring takes more time to plan and implement, making it more expensive. It may also require specialized skills and training.

A suggested format for qualitative and quantitative monitoring:

• Choose location to monitor. Begin monitoring where the bioagents were first released since this is where the highest density agents is likely to occur and therefore where changes to the yellow starthistle are more likely to be detected.
  
  
• Schedule monitoring activities. Schedule monitoring activities at the same time each year to be consistent and compare year-to-year variation.
  
  
• Determine a photo point. Establish a permanent photo point in the monitoring area. The photo point is an area where estimated cover and/or density classes of the yellow starthistle can be recorded. Be sure to label the photo point. Create a photo record beginning at the time of bioagent release and at 2-year intervals thereafter (called before-and-after photos). Trends and changes in the starthistle infestation and the plant community over time can be visually assessed with photographs.
  
  
• Plan. This step involves knowing what and how much data to collect before starting. Consult an experienced field technician, researcher or statistician for guidance on the design of your monitoring plan. The types of variables usually measured are one or more of the following:
  
  
• Visual estimates (qualitative). Record visual estimates of canopy cover. Determine the density and distribution classes of starthistles at the release site at 1- or 2-year intervals (distribution classes are seedlings, rosettes, bolted and mature). Fill out a qualitative monitoring report (see Appendix E). Personnel may have to be trained in estimating general vegetation attributes.
  
  
• Counts (quantitative). Count the number of seedlings, rosettes, seedheads, flowering starthistle plants within the quadrat (Fig. 41). Seeds can be counted from a sub-sample of heads (about 30 heads) within the quadrat.
  
  
• Measurements (quantitative). Measure plant height, stem diameter, plant circumference, etc.
  
  
• Choose a monitoring method. Choice of a monitoring method depends on the amount of time available to conduct the work and the monitoring objectives. Two methods of quantitative monitoring are transects and macroplots.
  
  
• Transect. A transect is a straight line measured on the ground along which vegetation is sampled. Transect lines can be as long as 300 feet (100 m) or as short as 30 feet (10 m). Vegetation along the transect is sampled or measured using a quadrat placed at regular intervals along the transect (i.e., every 10 feet (3.2 m). While transects are a more systematic method of sampling vegetation, the location of the transect can be random. Transects are faster and easier to set up and use than macroplots (see Appendix F).
  
  
• Macroplot. The purpose of the macroplot is to define a large area (e.g., 4 acres [1.6 hectares]) within which randomly placed small quadrats (1 sq. yd or 1 sq. m) are used to sample vegetation (see Appendix G). Although the macroplot is very useful and allows for sampling over a large area, it can cause considerable trampling by people at the site during sampling.

6.  Establishing Photo Points Photographs of the release site are a valuable assessment tool. Visual evidence of vegetation change over time is derived from comparing pictures of the same site taken from the same location, at the same time of year, with the same horizon, over a period of years. Records consisting of photographs are a qualitative form of monitoring and can be used

Figure 41. Monitoring yellow starthistle infestation (UGA1350043).

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