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Activity Ten
How Do We Know These Beetles Are Safe to Use? 

Objectives
Students will critically investigate the type of testing procedure used by the USDA when it determines that a new species of natural enemy may be imported for biological control of weeds. 

Method
In small groups, students will decide which ornamental and native or naturalized plants they want to expose to Galerucella spp. leaf-feeding beetles, a European natural enemy of purple loosestrife recently approved for release by the US Department of Agriculture. Simulating the host-specificity testing procedures used by USDA in the classroom, students will place Galerucella on caged plants and then observe, catalogue, and discuss insect and plant interaction during their life cycles. 

Background
Biological control of invasive weeds carries some risk, just as other methods of weed management, such as the application of herbicides, carry risks. Biological control scientists carefully apply procedures designed to minimize the risk of importing a weed's natural enemy that itself becomes a nuisance. What if the insect feeds on our preferred plants? Is this insect host-specific: will it feed only on the host weed, purple loosestrife? Given the large variety of plants found in our gardens, meadows, and wetlands, it was not practical for every preferred plant species to be tested before finally deciding to import a natural enemy to control invasive purple loosestrife, so scientists established a panel of experts to decide how to proceed. Under laboratory quarantine, three categories of plants were exposed to one of purple loosestrife's European natural enemies, Galerucella spp., to see if it was host-specific: 1) North American plants taxonomically related to purple loosestrife; 2) plants that live in the same wetland ecosystems as purple loosestrife, and; 3) selected crop and garden ornamental plants.

A close look at the life cycle of Galerucella reveals three critical observation points that can be used to predict the potential for negative impacts on non-target (preferred) plant species. The first is whether any amount of herbivory or defoliation occurs. Is there damage done? A second critical observation point is the ability of the newly emerged adults to feed and survive on a preferred plant. The third critical observation to make is the question of whether female Galerucella beetles can lay and mature eggs on the preferred plant. Two thresholds should be investigated: 1) Galerucella can eat the preferred plant enough to cause plant damage and 2) Galerucella can survive on the preferred plant? Observing the two organisms throughout their life cycle together provides evidence to help answer these important questions.

Now that European Galerucella spp. beetles are approved for use and have been released in this country we can only hope that our USDA panel of scientists made the right decisions about the risks presented by purple loosestrife and its insect enemy. Investigating and understanding the USDA host-specificity testing procedure, and extending this understanding to the student's selection of plants will lead to more informed decision-making when looking for ways to biologically control the next invasive species.

Materials
A minimum of one purple loosestrife specimen plant and it's natural enemies (described in Section 2 of the Cooperator's Handbook). Each small group will need one caged 2 gallon plastic pot, approximately 2 square feet of adequately lit bench space, and 10 adult Galerucella beetles for each preferred plant it wishes to test.

Procedure
"No-choice" testing of the student's preferred garden or wetland plants will require teacher coordination of beetle and plant life cycles so that beetles have foliage to accept or reject as food when they are placed in the cage. Timing of plant and beetle growth can be influenced by your control of temperature and photoperiod as described more fully in Section 2 of the Cooperator's Handbook.

A list of plants which have previously been selected for host-specificity testing is available from USDA and the PLP at MSU. Students may wish to repeat tests on these plants or select their own untested favorite plants without effecting your attainment of the objectives for this activity. Preferred plants can be obtained in stores, in family gardens, in the schoolyard, or in the wild. Student selection of plants will be limited by seasonal availability.

Remove any damaged foliage from the student's preferred target plant. Place ten newly emerged adult beetles in each cage with the preferred plant and after seven days remove the cage so the plant can be carefully examined for feeding damage or egg masses. Compare a representative leaf with any leaf found to be damaged by placing them on a 10 x 10 grid of 2.5 cm graph paper and recording the number of squares eaten. Count and record egg masses and the average number of eggs in each mass. Count and record the number of live adult beetles. Repeat this weekly until results stabilize.

Extensions
Additional preferred plant species can be tested throughout the year. Student research and reporting on plant/animal interaction, wetland ecology, the history of importation biological control, and risk management studies extend this activity.

Activities: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10