What Happens:

      In an initial 3-hour lab, students first design experiments to examine intraspecific and interspecific competition using two species of parasitoid wasps. Second, students are guided to a consensus experiment that examines the effect of both types of competition on reproductive output in the parasitoids. Third, the students conduct the consensus experiment in which one or two females are placed on a single host, alone, with conspecific competitors, or with interspecific competitors. Working individually, students set up replicate cultures of the experimental treatments. In subsequent labs, students check cultures for emergence of new adults and record date at first emergence. Cultures are frozen after full emergence, approximately 21 days for Nasonia cultures and 40 days for Melittobia and mixed species cultures. In a final, 3-hour lab, six weeks later, students gather data on the number of offspring produced by females under each condition. The resulting data are used to estimate the parameters of the Lotka-Volterra competition model. The predictions of the model are then compared to the outcome of interspecific competition treatments.

______________________________________________________________

Lab Objectives:

     At the conclusion of this lab, students will be able to...

1. Describe the life cycle of Nasonia vitripennis and Melittobia digitata,
2. Explain the possible interactions between two parasite species competing for the same host resource,
3. Design an experiment to determine the nature of the interaction between these two species when competing for a common host,
4. Conduct a consensus experiment to determine the effects of intraspecific and interspecific competition on reproductive output in Nasonia vitripennis and Melittobia digitata,
5. Use the resulting data to estimate the parameters of the Lotka-Volterra competition model,
6. Relate class research outcomes to the principle of competition exclusion.

______________________________________________________________

Equipment/ Logistics Required:

Materials for a class of 24 students (working in pairs):

• 1 - 2 cultures of Melittobia digitata (WOWBugs) newly emerged adults (Carolina Biological Supply, ER-14-4570, $12.85 for 50-100 wasp late stage pupae),
• 2 cultures of Nasonia vitripennis (Jewel wasp) newly emerged adults (Carolina Biological Supply, ER-14-4560, $10.75 for at least 50 wasps (you’ll need 2 cultures to be assured of a sufficient number of females),
• 72 Young Neobellierria (=Sarcophaga) pupae (Carolina Biological Supply, ER-17-3480, $11.85 for 100 - 150 hosts). (Although “flesh fly” is now the preferred common name, these are listed in the catalog as “blow fly” pupae). Note: if you are planning to use only hosts of a designated size, you will need to order a sufficient number of hosts to ensure that you have large enough supply of the size you are planning to use. In that case, you might consider ordering more hosts (Carolina Biological Supply, RG-17-3482, $22.80 for 200-250 hosts),
• 72 Glass shell vials, 1 dram, pack of 144 (Carolina Biological Supply, ER-71-5051, $20.00),
• Package of jumbo size cotton balls (purchase locally),
• Package of 24 pipe cleaners (purchase locally),
• Pack of fine tip permanent black marking pens (purchase locally),
• Aluminum foil (for making weigh boats - purchase locally),
• Electronic balance capable of weighing to nearest milligram,
• 25 sheets of plain white paper (purchase locally),
• Computer with statistical software, such as Excel.

Pre-lab preparations:

      Order the living wasp cultures and fly pupae to arrive at most one week before class. Wasps are shipped as late pupal stages and should be beginning to emerge upon arrival. If emergence appears complete upon arrival (i.e., numerous adult wasps crawling in culture container), cultures can be maintained fresh for short periods of time by storing them in refrigerator dairy compartment until day of class.

      Note: if you need a large number of parasites, you may wish to rear your own. See “Maintaining parasitoid wasp cultures,” below, for details.

      The Neobellierria (=Sarcophaga) pupae must be placed in the refrigerator immediately upon arrival and kept there until just before class use. Otherwise, they will begin to develop into flies and if this happens they are unsuitable as hosts for the wasps.

      The day before class, you (or the lab prep person) need to sort through the Nasonia culture removing all males, so that the wasps provided to the students are entirely female. This is necessary because the sexes are similar in appearance, and if the students are asked to distinguish between the sexes they are not always reliable. However, with a little practice males can be readily distinguished. Because the Melittobia digitata culture is always about 95% female and the tendency of males to remain inside the host pupal skin, there is no need to remove the males. There is little chance that a male would end up in an experimental vial. Male Melittobia are also extremely different from females, so in the unlikely event that one is found and chosen by a student it would be readily apparent.

See Notes to Faculty: Preparing Vials with Wasps of Each Sex to help students differentiate the sexes.

See Notes to Faculty: Instructions on Maintaining Parasitoid Wasp Cultures.

______________________________________________________________

Summary of What is Due:

      During the first lab period, students will produce an experimental design to examine the effects of intraspecific and interspecific competition on offspring production in two species of parasitoids. After collecting and analyzing the data, the students will write scientific papers based on their results.

______________________________________________________________

Keyword Descriptors:

Principal Ecological Questions Addressed:    What is the relative importance of intraspecific and interspecific competition in two species sharing resources? Does the Lotka-Volterra competition model accurately predict the outcome of competition between two species of parasitoids?

Ecological Topic Keywords:    intraspecific competition, interspecific competition, resource partitioning, Lotka-Volterra competition model, principle of competitive exclusion, parasitism, parasitoid

Science Methodological Skills Developed:    hypothesis generation and testing, statistics, graphics, data analysis, quantitative analysis, scientific writing

Pedagogical Methods Used:    guided inquiry, cooperative learning