Lesson Nineteen: Identification of Adult Insects Using Dichotomous Key

• Outcome
• Simple Dichotomous Key
• Simple Dichotomous Key for identification of certain Adult Insects

Outcome

• To identify representative insects from certain insect orders.
• Use dichotomous key to identify unknown organisms

Teaching Strategy:  Short guiding lecture and group work

The real identification is made by comparing the specimen with another specimen that is already named, or with a drawing, or with a good, detailed description.

Let the students compare these two insects on the bases of their external structures as an introduction.

Fig. 19.1:  External Structures of Adult Termite and Ant

It is often difficult to determine the difference between termites and ants. Termites have two pair of wings (front and back) and are of almost equal length. Ants also have two pair of wings but the fore wings are much larger than the hind wings.

Table 19.1: Comparison between external structures of adult termite and ant

Such kind of identification will initiate students for further identifications of organisms on the morphological similarities and differences using dichotomous key.

Simple Dichotomous Key

A dichotomous key consists of a series of two part statements that describe characteristic of organisms.  At each step of a dichotomous key the user is presented with two choices.  As the user makes a choice about a particular characteristic of an organism, it will lead to a new branch of the key.  Eventually the user will be led to the name of the organism that he/she is trying to identify.

Activity 1: Use dichotomous keys to classify unknown organisms

Divide students into groups. Allocate 3–4 unnamed pictures or specimens of organisms. Use simple dichotomous keys developed by teacher to identify kingdom, phylum and class.

Simple Dichotomous Key for identification of certain Adult Insects

1a.       Insect with wings..........................................................................2

1b.       Insect without wings.....................................................................7

2a.       Insects with four wings (two pairs)................................................3

2b.       Insects with only two wings (one pair)..........................................5

3a.       Wings covered with scales.......Butterflies and Moths OrderLepidoptera

3b.       Wings not covered with scales, though they may be hairy..............4

4a        Mouth-parts tube-like, adapted for piercing and sucking.......True Bugs OrderHemiptera

4b.       Mouth parts not adapted for piercing............................................7

5a.       Hind-wings reduced or modified to knob-like organs (called halteres) and mouth-parts of various forms........ True Flies Order Diptera

5b.       Hind-legs enlarged for jumping..........Grasshoppers Order Orthoptera

6a.       Small insects, generally much less than 1 inch. (25 mm.) In length with long  antennae, and with wings folded flat over body....... Termites Order Isoptera

6b.       Body flattened from side to side, hard and bristly, with strong legs, jumping insects,   found on birds and mammals........ Fleas orderSiphonaptera