A Little Bit More
During the summer, insects are often all too obvious. In the winter, however, we tend to forget that they’re still close at hand, we just can’t usually see them. As fall arrives, insects have several “strategies” for survival: they may migrate, hibernate, or enter diapause. Most insects rely on the latter two.
Dormancy (a state of inactivity) in insects is controlled by environmental and genetic factors. Some insects enter dormancy in response to environmental conditions (temperature, for example) that become unfavorable, and then resume activity when conditions are acceptable again. Other species are genetically “programmed” to enter a dormant period – called diapause – BEFORE conditions actually deteriorate. Diapause is usually initiated by photoperiod (day length); often a period of low temperature (winter) followed by a return to optimal temperatures (spring) is necessary to break this dormancy.
In the laboratory, caterpillars that normally build cocoons in late summer have been kept in the active feeding stage for up to ten years, simply by providing them with an artificially long day! Aphids that give birth to live young all summer but in fall change to egg laying, can be kept in their summer reproductive stage in the same way – by extending day length. It should be noted that the length of day for a given season varies in different latitudes and there is a corresponding variation in the onset of diapause within a species. How an insect knows when to emerge from diapause is not well understood, and much research remains to be done.
Activities
Insect Hunt
Objectives: Find some insects that are hibernating/in diapause
Materials: Suitable containers to house insec
Although you may think this exercise can only be accomplished with students living in suburban or rural areas, you’ll find that even in urban areas, there are many places where insects can be found in winter.
Tell your students that you’re going on an insect hunt at the time they’re least obvious so they’ll have to really be good at searching for them. Insects are all around, to be sure, but they are now in out-of-the-way places rather than where you might expect.
Have your students look both inside and outside if this is appropriate for your area. Many kinds of insects will find cracks and crevices that permit them to enter buildings so they’re not just in natural settings. You’re unlikely to find many insects but even if only a few are found, it should be interesting for everyone to see. If you don’t think your students can or should attempt this activity, you may want to do the scavenging yourself and bring in what you’ve found to share.
OUTSIDE
For locating insects outside, students can look in:
Tree bark, under rocks and boards, in dead leaves that are in somewhat sheltered areas, in a stream or small body of water, stone walls, compost areas, even underground.
INSIDE
For locating insects inside, students can look in:
Basements, cellars, corners of rooms (especially if not often used), garage, under steps, attics, any kinds of unheated outbuildings,
Any insects found (you’ll probably find some dead ones too) can be put in plastic bags, bottles, or other suitable containers and brought to class to share. Keep in mind that if some of these insects warm up (especially those brought in from outside) their activity level will increase considerably. You may want to keep these in the refrigerator ready to share and then when you’re finished, they can be returned to locations where they were found.
Once you have some in class, you may want to see how well you can identify the insect (field guides are very helpful for this) and also determine what stage of development you may have. Don’t be too quick to assume that what you’re finding is dead, dormant insects will often “appear” dead when they aren’t.
Key Concepts
Life Cycles, Behavior and Regulation, Adaptations and Diversity
Questions
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