Mealworm Culture

Introduction

Mealworms (Tenebrio molitor) are a clean, odorless and easy-to-maintain organism. Maintaining a continuous culture for a variety of classroom and animal feeding purposes is easy and inexpensive.

Concepts

• Metamorphosis

• Life cycle stages

Background

Mealworms are the larvae of the beetle Tenebrio molitor. During their life cycle, these beetles undergo complete metamorphosis—egg, larva, pupa and adult. What we normally think of as the mealworm (what we buy at the pet store) is the larval stage in the life cycle of a black-colored beetle. Students will be amazed how different the beetle looks compared to the larval form.

In the wild, the typical life cycle takes 12 months to complete, although it can vary from 4 months to 24 months depending upon the climate. Each female lays between 500 and 1,000 eggs on a viable food supply. The eggs are very sticky and hard to see since the food supply is usually a grainy, debris-type material. After about a week the eggs will hatch, but the larvae are so small that they are hard to see. The food source often looks like it is “moving” but the larvae might not be obvious. The larvae will molt several times as they grow and eat. Freshly molted larvae are an ideal food source for other organisms. The mealworms will usually remain in larval form for months and it is the stage found in your culture most of the time. Eventually, the larva form a pupa which will last for two to three weeks. The newly emerged beetle will be soft and light in color. In several days it will assume the typical black color of the adult stage.

Mealworms are ideal for classroom use and for illustrating an insect life cycle with complete metamorphosis (i.e., egg, larva, pupa, adult). A continuous culture is also an excellent source of supplementary food for other organisms. They are excellent food supplements for a variety of animals, such as fish, birds, bats, amphibians and reptiles.

Materials

Safety Precautions

Mealworms are considered to be a clean and safe organism. When working with any living organisms, it is always important to wash thoroughly upon completion of lab work. Wash work areas and hands thoroughly with soap and water.

Disposal

Never release live organisms into the environment. Old/dead culture materials can be disposed of following the guidelines for Type IV Biological Materials as outlined in the Biological Waste Disposal Section of your Flinn Science Catalog Reference Manual.

Procedure

1. Use a dissecting needle, ice pick, nail or other sharp object to poke air holes evenly about every inch in the entire top of the culture container lid. Do not make the holes larger than ⅛" or the adult beetles might crawl out of the culture. The larvae cannot climb the sides of the container.
2. Place about 2–3 inches of Flinn Mealworm Diet in the bottom of the culture container.
3. Use a cork borer (large size 10–20 mm) to bore a series of crossing tunnels in a large white potato. Take out about 5–6 cores from the potato. Bury the potato in the Flinn Mealworm Diet in the bottom of the culture container.
4. Introduce the mealworms into the new culture container. Simply pour the entire contents of the shipped culture into the container. Be sure to add all the debris that came with the active culture. The debris in the bottom of the container contains eggs and small, invisible larvae.
5. Store the culture in a place that gets neither too hot nor too cold (no lower than 40 °F and no higher than 90 °F). A temperature between 60–80 °F is ideal for long-term culturing. More rapid development will occur between 80–90 °F. To maintain a culture in a near state of dormancy, cover the container with a cloth to prevent condensation, and set it in a refrigerator at 40–50 °F.
6. Observe the culture periodically. When the potato dries up or becomes moldy, replace it with a fresh potato (apple slices and carrots can also be used). If a new colony is started, old pieces of potato may contain eggs and can be placed in a fresh culture for a while until new larvae appear. Unless the potato smells or gets moldy, leave it in the culture.
7. Over time, a buildup of powdery residue will appear in the container. This residue, called frass, consists of mealworm waste and eggs. This frass can be sifted through a piece of window screen or a strainer. The frass can then be placed in a new culture container with fresh potato, etc. and produce a new and viable culture. With care and periodic subculturing, you can keep your mealworms going forever! Subculturing and creating more cultures is necessary if the mealworms are being used as a food source for other organisms.

Teacher Tips

• This kit contains enough material to start a large, viable mealworm culture. Thousands of mealworms will be produced in the culture container provided. If the mealworms are being used as a food source for other organisms, other cultures should be purchased or this culture can be subcultured into other similar containers.

• The adult beetles are ideal for use in the classroom as a study organism for locomotion, feeding, physiology or other behavioral studies. Multiple cultures of mealworms, started at different times, will help ensure that adult beetles are available when needed.