Academic journal article Science Scope

Inquiry-Based Environmental Science Investigations with the Fantastic Fruit Fly

Academic journal article Science Scope

Inquiry-Based Environmental Science Investigations with the Fantastic Fruit Fly

Article excerpt

Children are naturally curious, constructing their own understandings about how the world works through observations and experiences with their surroundings. However, many of these self-constructed ideas are not congruent with scientifically accepted understandings and, thus, confound students' learning of science. Inquiry is an ideal method for teaching science because it requires students to consider their prior conceptions as they generate and explore authentic questions, develop investigations, and propose plausible explanations based on evidence. Through inquiry, students can develop a deep foundational understanding of science concepts.

The use of inquiry in life science can be particularly daunting because of the additional management and care living systems require. However, there are some low-maintenance organisms that work well in the classroom. One of these is the common fruit fly, Drosophila melanogaster. Its small size, low cost, easy availability and maintenance, and short life cycle make the fruit fly ideal for the middle school classroom. This article describes a two-part classroom inquiry investigation on population growth using fruit flies.

Meet the fruit fly

Like many insects, Drosophila melanogaster progresses through a complete metamorphosis in as few as seven days. The life cycle begins when the female lays up to 500 eggs on the surface of rotting fruit or other food. Within 24 hours of the female laying the eggs, small larvae emerge and feed on the food source for approximately three days. During this time, they pass through three larval stages known as instars. At the end of the larval stages, the immature flies pupate for an additional four days and then emerge as adults. The adult fruit fly has a black and tan body, red eyes, and, like other insects, is composed of a head, thorax, and abdomen. Because of its small size, a hand lens or microscope is needed to differentiate these details.

Preparing for fruit fly investigations

Conducting investigations with fruit flies is economical and easy. Most supplies are available from science supply warehouses, such as Carolina Biological (www. carolina.com) or Frey Scientific (www.freyscientific. com). Each group of two to four students will need 1 vial of 10 flies for an observation activity and at least 1 vial of 10 flies per test group for an experiment. One fruit fly culture from a science supply company will produce hundreds of flies in a matter of days, so be sure to order cultures in advance. Teachers may also culture fruit flies in the classroom or at home. This can be done by placing overripe pieces of fruit in a jar that has a tight-fitting lid with tiny holes added, using a nail, for air movement. Vials with foam stoppers may be purchased, or small plastic or glass containers, such as baby food or jelly jars, with tight-fitting lids can serve as an economical substitute. Natural food sources for fruit fly larvae include overripe fruit such as bananas or grapes. Be sure to check with your school nurse for any food allergies your students may have prior to bringing any fruits into your classroom. Any fruit will need to be replaced periodically in order to prevent mold growth. Another option is to use commercially available culture media that resist mold growth, which can be ordered from most science supply warehouses. Be sure to tightly seal any used fruit or culture media in plastic bags before disposal to prevent unwanted fruit fly infestations in your classroom.

It is difficult to observe fruit flies in their normal state because they are so small and mobile. It works best to anesthetize them and then employ sterile hand lenses, stereoscopes, or microscopes for observation. Fruit flies may be anesthetized inexpensively in one of two ways. One possibility, if a freezer is available in the classroom, is to supervise students as they place the container of fruit flies in the freezer in one-minute intervals for approximately 8-12 minutes, until the flies are anesthetized. …

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