Activity 11: Collecting and Hatching the Cocoons of Parasitic Wasps

by Brenda Hunt
8th grade biology teacher
Habersham County

Materials: Individual student journals for recording data, small plastic containers with plastic lids ( collecting jars with lids that can have air holes punched), tweezers, straight pins (for the teacher to use with the students), sugar, water, honey, vinegar, dead bugs, etc. ( a variety of food sources for students to experiment with and decide serves as the best food source.)

Purpose: Students will collect parasitic wasp's cocoons from the backs of the Catalpa caterpillars. Students will observe the cocoons and design containers and environmental conditions they feel will support the hatching of the wasps. Students will learn about what wasps use for food and about parasitic relationships. Students will develop a hypothesis for supplying the source for food or energy the wasp will need and how to deliver the food with the class. Students will make observations of wasps and cocoons after they hatch and compare similarities and differences in order to produce a simple classification scheme or key. Students should record all the information in their journal each time they observe their experiment.

Step One: Students will begin to notice many of the caterpillars have tiny white cocoons. These are from parasitic wasps laying eggs on the Catalpa caterpillar. The caterpillar's body actually serves as the food source for the developing wasp larvae in the cocoons. It is necessary to describe the parasitic relationship to the students. These are ectoparasites on the surface of the caterpillar. Students may be afraid since they are wasps but they need to be assured that these wasps cannot sting or harm humans. Show them the pictures of the wasps. Students or teacher can use tweezers to remove the cocoons. Students should carefully observe a number of the cocoons with a magnifying glass or dissecting scope.

Step Two: The teacher should tell students about wasps and what they normally use for food. Students should work in groups to develop a hypothesis about how to adapt the container and develop a food source to sustain the life of the wasp upon hatching. Allow students to share why they are making changes to the container. Hopefully they will decide on air holes and the teacher can bring them a pin and observe while they decide on how many, size, etc. Groups should label their containers so they can be recognized and allow students to compare methods used. Students will learn about what wasps use for food and about parasitic relationships. Students can count the number of days until their wasp hatch and then begin feeding them with the energy source they selected.

Step Three: Feeding the wasp presents a problem since opening the top will allow them to escape. Ask students to decide how to get the food in without allowing them to escape. The liquid sources can be inserted through the air holes on the head of a pin. Honey can be used to sustain the wasps allowing them to live up to 10 days. You may want to keep a stock of wasps alive yourself to use in step four, should all of the student's wasps die. 70% ethyl alcohol can be used to preserve the wasps in vials for reference and study purposes.

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