AUGUST
2008

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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08-28-08

Download the audio of On Six Legs: MP3, WMV.

Memories are Made of This: Insect Style

Learning is acquiring new information. Memory is when we retain what we learn. As I get older, it has become obvious that my memory is not as good as it once was. But I can still remember things from years ago. For instance, a song titled "Memories are Made of This." 

That song was written and recorded in 1956 by a group known as "The Easy Riders."  Dean Martin, Dave King and Petula Clark also recorded the song in 1956, and Martin's version reached No. 1 on the Billboard charts that year. Over the years, many other singers including The Everly Brothers, Frank Sinatra, Johnny Cash, The Statler Brothers, Paul Anka and Little Richard also recorded the song.

In the human mind, some memories linger longer than others. Sensory memory is related to the sense of touch, sight and smell. Such memory can best be described as very short lived. The memory lasts long enough for the organism to use or not use the information. Say to close an eye if the light is too bright.

Short-term memory applies to information that must be processed. Such as remembering driving directions or someone's telephone number long enough to write it down. Long-term memory applies to information or skills retained for long periods of our life. For example, remembering unusual events like the space shuttle disaster or how to ride a bicycle.

Sensory memory applies to all kinds of animals. But do seemingly mindless creatures such as insects have memories? Scientists say "yes." Certainly, insects learn. Insects such as butterflies learn the shape of preferred host plant leaves. Honey bees can learn the visual landmarks between the hive and a patch of flowers. Grasshoppers learn to avoid plants that upset their stomachs.

How long do insects remember what has been learned? Honey bees have been shown to retain information for several weeks. In humans, remembering something for a number of weeks might be called short term. Just long enough to allow us to pass a test in school. But for an insect like a honey bee, several weeks might be most of its life. So, relatively speaking, insect memory lasting that long would be like a human remembering the lines of a poem learned in grade school for 70 years or more.

An interesting example of learning in insects is the hissing behavior of the appropriately named Madagascar hissing cockroaches. These large-sized roaches get their name because they produce a hissing sound when disturbed, in an effort to ward off predators. When such a roach is picked up and handled, it likely will produce the hissing sound. However, after hissing for a short period of time, the roach seems to learn that it is not working and stops hissing. However, the next time the roach is picked up it is likely it will display a hissing fit all over again. Apparently, the roach has a short-term memory when it comes to the effectiveness of hissing as a deterrent to being handled by a human.

One of the most interesting questions in regard to insect memory is whether or not an insect could retain something learned as an immature into the adult stage. After all, insects go through a process called metamorphosis where most of the tissues of the immature are destroyed and reformed into the structures of the adult insect.

Apparently the answer is yes. Recently, scientists at Georgetown University discovered that a moth remembered what it learned as a caterpillar. Hornworm caterpillars were trained to avoid odors associated with a mild shock. When the moths emerged from the pupae, they also avoided the odors where the caterpillar had experienced a shock.

However, when caterpillars less than three weeks in age were exposed to odors and shocked, the information did not get transferred to the adult. I'm not surprised. I can't remember much of anything that happened to me, or that I did, before the age of 5. That is except for those things that my mother kept repeating in stories that I would just as soon not have known!

 

Writer: Tom Turpin
Editor: Olivia Maddox