The Fire Ants Book Discussion

1 Comment

Although I set an ambitious goal of Chapters 13-16, as you could probably gather, it took more time then I expected to digest the information in Chapters 13-15. Let's take a look at those chapters and save Chapter 16 for next week.

(For those of you jumping in late, we are discussing The Fire Ants by Dr. Walter Tschinkel by going over a few chapters per week. Click "The Fire Ants Book Discussion" category for related posts.)

Chapter 13. Another way for a queen to take over a colony

In addition to the drama of incipient colony foundation by independent queens discussed in the last post, Solenopsis invicta colonies have yet another way to gain reproductive success. Mature colonies produce a second set of reproductives in the fall, which overwinter in the nest. The overwintered females fly in early spring, under much different conditions than reproductives reared in the spring. The overwintered females try to take over established colonies that have lost their own queen, or have become orphaned. If they are not successful, the overwintered females are incapable of starting a colony of their own and simply perish. Tschinkel calls this type of behavior "dependent colony founding," apparently because the queen depends on the presence of orphaned mature colonies to be successful (?).

The overwintering females may also take over their own natal nest if their mother dies. In this case they do not mate, and produce only males. In orphaned colonies with overwintering females, 86% had unmated sisters for their queen, whereas 14% had queens that had stolen in from other colonies. When no overwintering females were present in the orphaned colonies, 62% had unrelated queens and 38% percent had sisters (top of page 189). I did wonder where those sisters came from if there were no overwintering females. Any thoughts?

Tschinkel reaches the conclusion that Solenopsis invicta is a "weedy species" because independently founding queens are much more successful in sites lacking competing mature colonies. Only 3% of colonies showed evidence of dependent founding. In contrast, Solenopsis geminata had a much higher success rate of dependent queen founding, with up to a third of colonies showing evidence of that type of founding.

What do you think of the technique of using match-mated females to determine the success of dependent founding queens?

Chapter 14. Colony Growth

How do you keep track of how an ant colony grows? In the case of Solenopsis invicta, you can start with even-aged cohorts by opening a new area to colonization. To get a count of number of workers, Markin drove a large cylinder into the soil around a fire ant colony and then slowly flooded out the workers. Tschinkel developed a method for sampling soil and ants from a colony during excavation. It is tedious and difficult work, which explains why so few of these types of studies have been undertaken.

The results suggest a colony on rough average reaches maturity around four years (and lives up to eight years), with around 200,000 workers.

As with individual organisms, temperature and the amount/quality of food available determined how fast a colony grew in laboratory conditions.

Did you find any points particularly interesting for this chapter? Anything I skipped over that you would like to discuss?

Chapter 15. Another aspect of colony growth: What types of ants are produced and when?

When a colony grows, it changes in composition as well as in worker number. The incipient colony starts out with tiny minims. Over time, workers of a range of sizes are added. Eventually the colony begins to produce reproductives.

Fire ants, in this case S. xyloni, have a range of worker sizes.

How much energy does a colony allocate to each type of ant? Tschinkel estimates, based on worker mortality, that a average fire ant queen produces 2.74 million workers during her lifetime. The colony's reproductive success depends on optimally allocating resources between workers and reproductives. Too many workers, and the colony loses opportunities to reproduce. If there are too many alates, there won't be enough workers to feed them all.

As a colony grows and becomes mature, a higher percentage of the workers are the large or major workers. He only briefly mentions juvenile hormone as a possible mechanism in the switch to larger workers, as well as level of food.

Do you know of any recent research that sheds more light on this topic?

Tschinkel also disscusses how the nest grows with colony size and how the size of the colony's territory changes as well. He ends with a summary of how the colony ends, which he describes as resulting from the queen likely running out of sperm and thus being no longer able to produce replacement workers or female alates.

Do you have any comments on Chapter 15?

Interlude: The Porter Wedge Micrometer

A device for measuring 200 head widths of ants in one hour? Sounds like a dream come true. What do you think of Tschinkel's idea that it has been slow to catch on due to "cultural viscosity?" I admit I did it the old-fashioned way, but I pinned all my specimens first. Now that was tedious!

Have you tried a wedge micrometer? How do you measure your ant head widths?

Let's try to cover Chapters 16 and 17 this week, with the Interludes (up to page 271). Is anyone further along than that? Let us know, and I'll try to move ahead more quickly.

Some chapters/text of The Fire Ants is available online at Google Books.

5 Comments

Do you agree that 10-12 are the best chapters yet?

(For those of you jumping in late, we are discussing The Fire Ants by Dr. Walter Tschinkel by going over a few chapters per week. Click "The Fire Ants Book Discussion" category for related posts.)

Chapter 10 covers mating swarms and colony foundation by new queens.

In many ways Solenopsis invicta follows the classic ant colony foundation script, at least at first. Males and unmated queens are produced in spring and hang around in the nest until conditions are right. Mating flights are triggered the day after there is a locally heavy rain. The workers start to mill around while the males and unmated queens fly from the nest. After mating, the queens fly some distance (from monogyne nests) and then land at a suitable location to start a new colony. For the males, it is a dead end trip. The mating swarms occur most frequently in May and June, but can take place in any month if conditions are right. Not all the reproductives leave in any one swarming event.

A fire ant queen prefers to land on a roadside or recently disturbed land, although she sometimes ends up in a parking lot (see Interlude below) or swimming pool. If the local conditions are suitable upon landing, the queen immediately removes her wings. She searches for a place to begin digging and prepares a hole by removing soil with her mandibles. She creates a chamber and crawls inside for a typical claustral, or closed inside a chamber, founding.

Here in Arizona, both ants and termites are sometimes induced to swarm by sprinkler irrigation. Tschinkel indicates that fire ants can also be induced to swarm artificially by applying water.

Have you ever seen fire ants swarming?

(Photograph by April Nobile / © AntWeb.org / CC-BY-SA-3.0 from Wikimedia.)

Chapter 11. Claustral Founding

Once the newly mated queen loses her wings, the proteins from the wing muscles begin to deteriorate and, with the storage proteins and fats already residing in her body, are used to fuel the development of eggs. She lays 20 to 100 eggs in the first week, some which are trophic eggs that serve as food for the larvae when they hatch. The queen cares for the eggs, larvae and pupae until the first workers emerge. The first workers are always extra small workers called "minims."

Now come the interesting part, where fire ants begin to diverge from the traditional ant colony founding script.

Upon landing, some of the queens form founding associations with other queens. Tschinkel was able to show that this behavior was density dependent, meaning the more queens in a given area, the more queens founding in groups. He was also able to show that a pre-formed hole of the proper depth and dimensions was highly attractive to fire ant queens. (Cool!)

Queens that found in groups tend to produce fewer minims per individual, but also weigh more at the end of the claustral period. Weighing more has an advantage during the next stage.

Interlude:  What do you think about the essay "Sharon's House of Beauty?" Why do you think the fire ants are attracted to such a site?

Chapter 12. Brood Raiding

Now the script becomes more like one for "Desperate Housewives." Once the minims have emerged and the many incipient nests are opened to the world, the tiny colonies begin a process that results in only one nest with one queen.

As soon as the minim workers are active, the queens of nests with multiple queens start to fight. Over time one queen wins by dominating the brood pile. Often she's the heaviest queen. Others are pushed away, where they are more likely to be attacked and killed by workers. The result is a nest with one queen.

At the same time, the minim workers may wander from incipient nest to incipient nest. The minims do not fight with minims of other colonies, as would be the case for larger workers from more established colonies. Eventually workers from colonies with a larger number of minims act like very rude guests, pick up brood from other nests they visit and bring it back to their own. The minims from the raided nest may go retrieve their sisters and take them back to their initial nest. The workers from the competing nests may go back and forth for a time. but eventually one colony wins and all the minims and brood end up in the winning nest. Then the raiding begins in another nest, until all in a given area are combined into one. Tschinkel recalls one raiding series where 80 incipient colonies consolidated into just two.

As Tschinkel points out, the behavior of minims of abandoning their own mother to join another unrelated queen seems to fly in the face of evolutionary theory. His suggestion is that because the abandoned queen tends to move to the winning colony where, if she is able, she joins the colony and may eventually take over, the minims have a small chance of having their mother be the winning queen even if they leave their natal nest.

What do you think of this period in the colony founding process? What about the idea that the minims are moving because of the small chance their mother might win? Wouldn't it make sense that the minims would stay with their sister brood rather than their mother because they are more closely related to their sisters than their mother?

Any other questions or comments?

How about reading Chapters 13-16 next?

Anyone ready to discuss chapters 7-9, plus the Interlude, Mundane Methods? (For those of you jumping in late, we are discussing The Fire Ants by Dr. Walter Tschinkel by going over a few chapters per week. Click "The Fire Ants Book Discussion" category for related posts.)

Chapter 7 is about the fire ant nest. The construction and shape of the fire ant nest varies with a number of factors, including season, soil type and weather.

In general, a founding colony starts out with a simple tunnel, and as the number of workers increases, the number of underground tunnels and chambers increases. Solenopsis invicta colonies dump the excavated soil onto the surface, forming a dome-shaped mound. Unlike many other ants, they actually build tunnels in the mound and utilize it, especially during the winter months.

Below is a photograph of a zinc cast of a Solenopsis invicta nest within the above ground mound of soil. This is a negative impression, meaning the space of the tunnels has been filed with zinc and the surrounding soil has been removed.

Do you think that this use of the excavated soil comes from the fact Solenopsis invicta is from an area that floods frequently?

Anyone have comments about this chapter or the Interlude, There's Nothing Like Getting Plastered? Tschinkel is well known for his casts of various ant nests. What do you think of his idea that we need to learn more about the nest structure or architecture as a way of understanding social insects?

Edit:

And I just found a video of this:

Chapter 8. Looking at fire ant territories.

In addition to the nest itself, most ants also occupy an area around their nest that is used for foraging. This forms a territory, from which ants from other colonies are typically excluded. The size of the territory is usually dependent on the size of the colony (number of workers), as well as presence of neighboring colonies. Interestingly, fire ants have extensive underground foraging trails throughout their territories

This chapter is especially useful because it discusses the methods used to study territoriality in ants.

What do you think? I am still mulling the relationship of nest tunnels to underground foraging tunnels.

Chapter 9. What fire ants eat.

Like many other ant species, Solenopsis invicta workers are predators of arthropods, scavengers and exploit whatever sweet liquids are available within their territory. We already talked a bit about whether fire ants tend aphids. Tschinkel suggests that the ants exploit extrafloral nectaries and root-feeding homoptera for sugars.

(If you were wondering about fire ants and vertebrates, Tschinkel saves that for chapter 36.)

According to a study by Tennant and Porter (1991), fire ants carry liquid food back to the nest about 80% of the time.

We tend to think of ants storing food in their social stomach, the crop, but Tschinkel reminds us that ants can also store excess food as fat, the typical animal food storage molecule, glycogen, and also as storage proteins, such as hexamerins.

Anything surprise you in this chapter?

Interlude:  Mundane Methods

Okay, I admit it. I loved this part. It made me laugh out loud, especially the part about ant hotels on page 132. Who hasn't had their ant workers decide to move into another laboratory/building/office on a whim?

Do you have any ant wrangling tips to share?

So, how are you doing? Are you ready to move on the read Chapters 10-12, about the founding of new colonies? Or has everyone gotten too busy and/or lost interest? (I have to admit I have been distracted a bit by Army Ant Week over at Myrmecos.)

Reference:

Tennant, L.E. and S.D. Porter. 1991. Comparison of diets of two fire ants species (Hymenoptera:  Formicidae): Solid and liquid components. Journal of Entomological Science. 26:  450-465.

6 Comments

Anyone wade through chapters 4-6 of The Fire Ants yet? If so, let's get started. (For those of you jumping in late, we are discussing the book a few chapters per week. Click "The Fire Ants Book Discussion" category for related posts.)

Chapter 4. A summary of the current thinking about where, when and how the various fire ants arrived in the southern United States from parts of Argentina and/or Brazil in South America.

Basically, it appears that one species of fire ant, Solenopsis richteri, was introduced to the port city of Mobile, Alabama area around 1918 and what we now know to be Solenopsis invicta showed up in the same area in the early 1930's. At the time the two species were thought to be two color variants of the same species, and the lighter-colored Solenopsis invicta was called the "red imported fire ant." It is interesting to ponder why the fire ants established only in Mobile, rather than in other nearby, and presumably similar, ports such as New Orleans and Pensacola.

The area of South America where Solenopsis invicta originated is also the home of several other migrant species of ants, including the Argentine ant, Linepithema humile, and my personal backyard "pet" ants, Brachymyrmex patagonicus, the rover ants.

In a way, this chapter is also about the formative years of E.O. Wilson, as well. Can you imagine the excitement/dismay of following the spread of Solenopsis invicta through your home state?

Does anyone have any more recent information to add? How about the genetic analysis of the central South American species? Are there any recent insights about the introduction/taxonomy that you would like to share?

Chapter 5. The historical spread of Solenopsis invicta and the eradication programs to eliminate it.

Time to admit a bias. I studied with W.L. Brown Jr. at Cornell, and he told about the mistakes of the fire ant eradication programs from the first week I arrived. He explained how using Mirex to kill fire ants had actually increased the rate the fire ants were able to spread. These days any pest management book or class will talk about pest resurgence, although at the time it seemed counter intuitive. How could a pesticide that killed a pest cause it to explode in numbers? Now we know that fire ants are a weedy species that thrive where other ants are knocked out, which is exactly what Mirex did. We killed the fire ants' competitors for them.

Bill Brown wrote some of the early papers on the subject.

W.L. Brown Jr.  (1961). MASS INSECT CONTROL PROGRAMS:  FOUR CASE HISTORIES. Psyche. (click on link towards top for a free .pdf)

What do you think of the fact that Mirex was used in the 1970's, only roughly a generation ago? Mirex is very persistant and moves through food chains like other chlorinated hydrocarbons.

Chapter 6. Where is Solenopsis invicta going in the future?

Maps are always fun.

This one is from 1982 by Strongbad at Wikipedia.

Map of the  status of Solenopsis invicta from Purdue.

In this case, the purple colors indicate establishment, green is areas that are fire ant free. Go to website for more information and yearly maps.

Tschinkel goes into quite a bit of detail about the biological requirements of Solenopsis invicta, and how that will probably limit their future distribution.

Tschinkel does not mention the effect of competing ants. Do you think that may be a factor in areas where the environment is marginal? What about Argentine ants in California? Is it going to be the battle of the South American ants instead of ant eradication by humans?

What are your thoughts on these chapters?

Let's read Chapters 7-9 next, with the interludes. Tschinkel explores what a fire ant colony needs to survive: shelter, space and food. If you read nothing else, be sure to read the interlude, Mundane Methods on page 130.

I'm going slightly off topic. Blame it on too little sleep.

A few months ago when I first read these chapters, I had the distribution maps above and from the book on my mind.

Then I saw this map of the distribution of ADHD prevalence of treatment from the CDC (2003):

Comparing the purple areas above with the dark red areas here... I'm not saying fire ants cause ADHD... But, well, hum.... weird.