For this lesson you are going to use a web site that is part of an undergraduate physiology course at Davidson College. This particular page was created by Chris Thawley. Read the assigned sections, answer the questions, and once you are finished send me your work as an email attachment in MS Word (.doc) or Rich Text Format (rtf) format. Go to the “Hot Topics” web site and find the link to Thawley’s page titled Endothermy in Hymenopterans. You will find it near the bottom of the web page.

Read the main page to learn some general information about the insects that are classified as Hymenopterans. They are familiar insects that you have seen many times. Don’t be put off by the strange terminology of the first paragraph. Entomologists (scientists who study insects) are overly fond of terms for every detail of insect biology. Concentrate on the point that the diversity of these insects and their habits are linked to endothermy.

Flight Adaptations

Now follow the link to “flight adaptations” and read this section. Pay particular attention to the relationship to between the insect’s ability to fly and their ability to generate and transfer heat in different parts of their bodies. Understand the role of the thoracic flight muscles in generating heat and the role of the abdomen in regulating heat loss. This section mentions a countercurrent system. We will discuss this concept in more detail latter this year. It turns out that many organisms including humans (our kidneys for example) utilize counter current mechanisms. Study the graphs in this section.

Winter Adaptations

It has been known for many years that bees can survive in their nests by generating heat. This section gives you some details about this process. Not only do the bees generate heat with their flight muscles, they engage in behaviors that benefit the entire group not just individuals. This “altruistic” behavior of individuals is one of the hallmark characteristics of the social insects; especially ants, bees, and wasps. Study the graph in this section.

Reproductive Adaptations and Reproductive Benefits

These sections could be better called “Life Style Adaptations” because they really deal with how bees living in different environments have adapted their life cycles including reproduction to cope with temperatures that would prevent most insects from surviving. The last paragraphs deal once again with the countercurrent heat exchange mechanism. In this case rather than keeping heat in the thorax to maintain the temperature of the flight muscles, heat is moved to the abdomen to speed up the development of the ovary and eggs.

1. Who are the Hymenopterans? Simply name some of the common insects of this group that you are familiar with from your every day experience.
2. Briefly describe three different mechanisms by which bees can regulate their body temperature. Indicate which of these mechanisms involve internal physiological, anatomical, or behavioral adaptations
3. Many insects get by without producing elevated body temperatures. In terms of its flight mechanisms, why do these insects require such a high body temperature to fly efficiently?
4. The first graph shows thoracic temperature vs. time. Compare the maximum temperatures attained by these insects compared to normal human body temperature. You may have to convert the Celsius temperatures in this graph to Fahrenheit to make a comparison.
5. The circulatory system of these hymenopterans is used to transport heat after it is generated by the flight muscles. Briefly explain how this works when the insect is in a cold environment and when it is in a warm environment.
6. An important point made by the author is that the presence of endothermy has permitted the hymenopteran insects to move into environments that would otherwise be inhospitable to them. Explain this and give to specific examples. Include a brief comment on the costs of endothermy that may have limited the evolution of endothermy to only a few groups of insects (think energy=food).

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