Activity - Friend or Foe? You Ought to Know?

Skills: Observing, Classifying, Ordering, Reasoning
Activity - Friend or Foe? You Ought to Know? - Articles

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Overall Learning Objectives

  1. Learn basic types of life cycles of insects and how that relates to their food sources.
  2. Understand what molting is and why it's important.
  3. Learn basic types of mouthparts of insects and why their important.
  4. Learn basic insect habitats and sampling techniques.
  5. Learn to use a key to distinguish major Orders of insects.
  6. Understand relevancy of insect biology to Integrated Pest Management.

Background

Insects: Who are they?

Insects may be small but they are obviously very successful creatures on the fact of the earth! Their ability to colonize new habitats and exploit all resources are a result of a combination of characteristics not found in other organisms. Some of these are:

  • small size (lots of them can fit into a specific habitat)
  • "cold-blooded" (requires less food for maintenance)
  • wings (they can move long distances)
  • specialized feeding (different species divide up which resources used)
  • complex life cycles (different life stages use different resources)
  • creative reproductive strategies (many can increase very rapidly)

The activities in this section will help your students learn more about these characteristics of insects and how they relate to an IPM approach.

Insects are class members of a larger group of creatures, the arthropods. Besides insects, commonly recognized classes of arthropods include various crustaceans (e.g. crabs, lobsters), the arachnids (scorpions, spiders, ticks, mites, daddy longlegs) and two other groups including the millipedes and centipedes.

You can recognize adult insects from other arthropods by four main characteristics:

  • 3 body parts (head, thorax, abdomen)
  • 3 pairs of legs
  • 1 pair of antenna
  • wings (2 pair, with some exceptions)

Insect immatures, or larvae, are typically much more difficult to distinguish from one another. Sometimes, it is hard to even believe that a particular insect larva and the adult are even related!

Insect Life Cycles and Growth

Insects go through two basic types of life cycles:

1. Complete Metamorphosis in which there is an egg, larva (young) and adult stage. In this type, the larva looks nothing like the adult and does not even eat the same kind of food. (Just like our kids!) The most commonly recognized example is: "egg - caterpillar - butterfly".

But there are others, such as:

  • "egg - maggot - fly"
  • "egg - grub - beetle"
  • "egg - larva - honeybee"

Complete metamorphosis allows an insect species to make use of multiple habitats. Caterpillars, for example, feed by chewing on leaves. Their parents, butterflies and moths, feed by sipping nectar from flowers through long tubelike mouthparts. Talk about a generation gap! Also, insect larvae typically do not have wings, antennae or 3 distinct body parts. Some, like maggots, don't even have noticeable heads or legs. However, when larvae do have legs, they have 3 pair of "true" legs just behind their heads - sometimes this is your best clue that the "worm" you are looking at is an insect.

2. Incomplete Metamorphosis in which there is an egg, nymph (young) and adult stage. In this case, the "nymph" looks like a miniature version of the adult but without wings. This is typical of the "true bugs", grasshoppers and crickets, termites, cockroaches and others. In other words, there IS such a thing as a "baby" grasshopper but not a "baby butterfly" - young butterflies are caterpillars!

Growth

Insects have a hard outer "shell", the exoskeleton, so they have to do some tricky things in order to grow. In order to expand, insects have to form a new skin under the old, split and shed their old skin, expand and harden their new skin. This whole process is called molting. Activity 4 demonstrates how this works.

Insect Feeding Habits

You name it, insects eat it. Their small size and varied mouthparts allow one species or another to take advantage of almost any food resource: roots, seeds, stems, leaves, flowers, decaying organic matter, hair, blood, feces. Activity 5 demonstrates how insects have divided up what they feed on using their different types of mouthparts. Because of specialization of diet, one finds different kinds of insects in different habitats or filling various "niches" in the environment. Insects are important links in ecological food webs. Activity 6 allows students to see this for themselves by learning the sampling techniques to use in different habitats and looking at the types of insects captured.

From and IPM point of view, it is important to know the feeding habits of the various insects encountered. This tells you which types of insects are associated with which types of damage and indicates which control tactics might be effective.

Insect Identification

In Activity 7, students use insects collected in Activity 6 and learn how to distinguish the major Orders on insects using a key. Besides learning about the amazing diversity of critters all around us, insect ID is important to effective IPM planning.

Introduction

Learning the true identity of an organism opens a whole world of information about it to you - as long as it has been described and studied before! (Actually, there are probably thousands of insect species in the U.S. alone that have never been "discovered".) Once you have a general idea about the type of insect you have, you can find out more about it where and how it lives, what it might eat, its reproductive potential and more.

Using more sophisticated keys and picture guides can help you identify the critter even more closely - sometimes down to the exact species. Insect identification is a good way to familiarize students with scientific nomenclature, or the system of naming. Each species has a "first" name and a "last" name. The first name indicates the Genus, a broader group to which the organism belongs. This part of the name is capitalized. There can be many members of a given genus. The second name tells what exact species the organism is. This name is not capitalized and not shared by any other species. Typically, both names are underlined or written in italics.

The words themselves are usually derived form Latin or Greek and describe characteristics of the organism. The genus name is a noun (e.g. "dog") and the species name is an adjective describing the noun ("barking").

Thus, we have

  • Canis latrans = "barking dog" = coyote
  • Canis familiaris = "domestic" dog
  • Canis stupidis = "stupid" dog (no, just kidding!)

Terms in insect classification at the level of Order, often refer to some characteristic of the wings. Wing in Greek is "pteros" so the Order name, Orthoptera means "straight" (ortho) and wing. (See background materials).

Learning Objectives

  1. Become familiar with using "keys" to identify insects
  2. Learn to identify major Orders of insects (and Classes of arthropods)
  3. Learn how to preserve and pin specimens
  4. Become familiar with scientific nomenclature

Materials Needed

  • Insects, dead
  • Insect pins
  • Corks and / or pieces of Styrofoam
  • Petri dishes
  • Ethyl alcohol
  • Dissecting microscopes
  • Paper & pencil for labels
  • Small paint brush for handling small, soft-bodied creatures
  • Insect keys and pictures or books

Timeline: At least 1 hour, preferably more.

Procedure: To be described in class.

Data collection:

Non

Illustrations:

Number of Living Animal Species Currently Known