LESSON 3: Prolegs, Head Capsules, and Warts
SUBJECT: Science
OBJECTIVE: Students will learn some identifying features of the black cutworm larvae and understand why such small details are so important.
MEASUREMENT: Students know that a worm is not just a worm. If they look closer, it might be a larva with many specific, identifying factors!
BACKGROUND FOR TEACHERS:
The scientific name for Black Cutworm is Agrotis ipsilon. This insect is in the Order Lepidoptera which includes butterflies and moths, and the Family Noctuidae which is the largest family in the order, with over 20,000 species, over 2700 in North America. Many are common moths, and although they vary in size and color, most have a wingspread of 20-40 mm and are dark-colored.
Noctuid larvae are smooth and dull-colored and most have five pairs of prolegs; a few, called loopers, have only three pairs and move like inchworms. Larvae of some species (cutworm) feed on roots and shoots of plants, and often cut off the stem just above the ground. Larvae of other species (corn earworm) feed on growing ears of corn, tomatoes, and cotton bolls.
In terms of economic damage to crops, the Noctuidae family is easily the most significant.
Noctuids are nocturnal and the moths constitute a major proportion of insects attracted to lights. The larvae are also nocturnal, emerging at night to chew through stems or other food source.
The life cycle is one of complete metamorphosis, meaning it progresses from egg to larvae to pupa to adult. The larvae are the destructive stage for corn producers and the only stage diagramed in this lesson. (See Unit 3, Lesson 2 for information on the time required to move from one growth stage to the next.)
The size of the head capsule is an indicator of the size of the larva, and how much damage it can do before it quits eating corn, and pupates.
Proper identification of insects is essential for proper management. In cornfields, black cutworms are often confused with larvae of the crane fly, which have no legs as compared to the prolegs of the black cutworm. They're also confused with dingy cutworms, which are less aggressive feeders and so do not require the same degree of control. The paired tubercles, or "warts" on dingy cutworms are both the same size, as compared to black cutworms, in which one is much larger than the other.
STUDENT ACTIVITIES:
1. Ask students to read the story, Elizabeth Sees a Bad Side to Her Favorite Creatures, paying close attention to the descriptions of the black cutworm moths and worms (larvae).
2. Show students the picture of the moth and explain that the moth lays the eggs that hatch into the larva (worm) you're going to study. Explain that after the larva grows to its full size it pupates into another moth. The cycle of complete metamorphosis is therefore: egg to larvae to pupa to adult.(Example 1) Again, the size of the head capsule is a way of measuring a larva's size, and knowing how soon it will pupate. In the case of black cutworm, the moth does not overwinter in the north, but relies on strong southern winds to bring it back in the spring.
3. Use the example of student's fingerprints to emphasize that small details can be very important for proper identification. Explain that there can be more kinds of insects in one acre of land than species of birds in the entire United States, as many as several million, and it is very important for farmers to know exactly what insect they need to manage. There are different management systems or pesticide treatments for different insects.
4. Mistaken identities can cause lots of problems. Students can discuss some of the possible consequences. They can also understand why farmers hire crop consultants or other advisors to help identify insects, weeds, and diseases in their cornfields. |
KEY ISSUES
