Monthly Archives: December 2013

When I was on a historical tour in China, I visited an antique silk factory in Fujian, China. Inside, there were swaths of unfinished silk rolls and a small shop selling a multitude of silk products. One of the main attractions was the beauty cocoons, as women grabbed as many as 10 bags while excitedly boasting the cocoons’ anti-aging and skin firming effects. Detailed instructions on using beauty cocoons can be found here.

Silk Beauty Cocoons. Photo Credit: Me!

The Bombyx mori, or the domesticated silkmoth, is part of the order Lepidoptera. Silkworms primarily eat mulberry leaves and their silk cocoons feed the booming demand for silk in the textile manufacturing industry. Perhaps alluded to by the tragic tale of Pyramus and Thisbe, where the gods stained the fruits of mulberry trees red to honor their star-crossed love, the silkmoth is also cursed with an ill-fated life.

Despite their proclaimed skincare benefits, silk beauty cocoons are obtained by boiling the cocoons of silkworms, killing the larvae inside. In fact, even if silkmoth caterpillars are allowed to live past their pupal stage, silkmoths emerge blind and have become so dependent on human captivity that they can no longer fly. However, misery loves company, and the Attacus atlas, better known as the Atlas moth, also succumbs to a similar tragic fate.

The Atlas moth looks like a small bird from the distance, with a record wingspan of 262 mm. The Atlas moth is a Lepidopteran with the largest known wing surface area, though not the longest wing size. While the unbroken white silk of B. mori is highly prized, the light brown silk cocoons of A. atlas is also widely used and harvested. These two types of silk have comparable physical properties, but differ in their chemical composition. The cocoons of A. atlas larvae are composed of broken strands of brown Fagara Silk, a durable silk used in clothing and purses.

Brown Silk Cocoon. Photo Credit: http://www.flickr.com/photos/33465428@N02/4917005478/.

The A. atlas does not only share its beautiful silk cocoon with the B. mori, as the Atlas moth also lives an unfortunate life. Although the Atlas moth does not emerge from its cocoon blind, its adult form lacks mouthparts, preventing it from eating. Instead, the Atlas moth feeds off its larval fat supply and consequently lives for only 1-2 weeks. Their extremely large size is also a disadvantage, and they must spend their short lifespan evading predators whilst trying to reproduce before they die.

Wingtips of the Atlas moth are similar in appearance to a snake's head. Photo Credit: http://www.learnaboutbutterflies.com/Caterpillar%20-%20Attacus%20atlas.htm

Despite the slew of misfortune the Atlas moth faces, they also have heavy defense mechanisms. When in danger, the Atlas moth will drop to the ground and fan its wings, using its wingtips to imitate the appearance of a snake’s head. The A. atlas larvae will also secrete a defensive irritant when its hemolymph pressure increases, as when it is attacked by predatory ants or birds.

Although we can sympathize the plight of the Atlas moth, the parallels between A. atlas and B. mori foreshadow future complications from human interference with insects. Like the harmful domestication effects on the silkmoth, I can only hope the Atlas moth will not meet the same end.

“We can’t live them; we can’t live without them!” This is probably one of the most appropriate quotes when applied to ants.

This year I live on the 1^st floor of Martel, which basically means that my “unofficial” roommates are from the class Insecta.  I have seen my fair share of spiders, dandy long legs, and cockroaches! Well, recently, I have come across the infamous ants!  I was enjoying a nice shower after a long, cold day at school, when, all of a sudden, a line of ants appeared on my shower wall!  Being the irrational coward that I am, I freaked out and ran straight out of the bathroom! Luckily, I didn’t see the ants for a few weeks, but now the ants started reappearing out of nowhere! UGH!

The little black ants that you see around campus are most likely Monomorium minimum.  They are rather harmless and play a huge role in our ecosystem.  They are scavengers that feed on bird droppings, dead insects, and leftover food.  Unfortunately, those aren’t the only insects that inhabit Houston. In fact, there has been an increase in the diversity of ants in Houston!  Particularly, a new invasive species you may know as the “tawny crazy ant” or formerly the “Rasberry crazy ant”, have made its way to Texas, Florida, Louisiana, and Mississippi! It’s rapidly spreading across the southern region of the United States.

Photos taken by the Joe A. MacGown/Mississippi Entomological Museum

The “tawny crazy ant” is originally from South America, specifically Argentina and southern Brazil.  Due to the increase in trading with South America, a few of these tawny crazy ants were able to get into America.  The scientifically accepted name of the “tawny crazy ant” is Nylanderia fulva and it is known to be the most aggressive invasive species in the world! (You really don’t want to mess around with them) From electrical wires to livestock, they have a niche for everything.  The “tawny crazy ants” damage electrical equipment by forming bridges between the electrical currents, which in turn, causes it to short out.  One good thing about Nylanderia fulva is that they don’t sting.

Photo of a "tawny crazy ant"

The “tawny crazy ant” is successful for multiple reasons.  Firstly, they are highly competitive and adaptive.  They can easily turn foreign land into their home. UT researchers studied the invasion of tawny crazy ants in a fire ant dominated location and saw that the tawny ants were able to completely eliminate the fire ants in that region.

Furthermore, it has been suggested that they have secrete a very potent chemical for defense and offense.  Like other ant species, Nylanderia fulva produces formic acid in their poison glands, but they produce more than two orders of magnitude of formic acid compared to other species. Thus, they can easily kill off other species in the same area, making them a very strong competitor.

 Clearly, this is an issue because the tawny crazy ants are rapidly reducing the diversity and abundance of insects.  In addition, it is very difficult to get rid of these pests! The tawny crazy ants do not readily ingest the poison bait that we often use to control fire ant mounds. They also don’t form the same type of colonies as other ants, making it difficult to kill a population. They take up a large amount of space and they are not particularly organized; they spread out randomly and have loose trails.   

In short, we find ways to stop this invasive species from spreading becaues they are not only harming us, but they are also harming our fellow Earth residents!

Check out this video showing the aggressive behavior of the tawny crazy ants!!

When I was at home in Dallas over this Thanksgiving breaking, I noticed that the weather was unusually warm, or at least not as cold as other Thanksgiving weekends I have experienced in the past. I also saw an unusually large amount of insects for this time of the year, and I imagine that it is partly because of the unusually warm temperatures.

Having done a bit of research into the matter, it is not surprising, then, that insect abundance and distribution are partly regulated by abiotic factors, chiefly temperature and humidity (http://www.hindawi.com/journals/psyche/2012/167420/). Both of these factors were noticeably well above average for this time of year in Dallas.

A study by E. Muller and E. Obermaier observed the effect of daily exposure to a variety of temperatures on the beetle species Galeruca tanaceti, with results indicating that average temperatures close to or below the developmental threshold retard development and in many cases increase mortality (http://www.hindawi.com/journals/psyche/2012/167420/). I saw an unusual abundance of insects for the time of year, but the insects did not look very healthy at all. I hypothesize that this warm front ‘tricked’ the insects into thinking that spring was already here, and the lack of consistent, sustained warm temperatures along with predictable undernourishment caused the larvae to result in unhealthy adults.

Another study led by E. Penarrubia-Maria explored how long into winter the Mediterranean fruit fly, Ceratitis capitata, would persist. Results indicated that this species of insect was unable to withstand temperatures once they dropped below freezing (http://www.hindawi.com/journals/psyche/2012/497087/). I find it fascinating that the presence of insects in the later months of fall can be used to determine how cold of a fall a habitat endured, even if one has not even been in the habitat. Based off of my observations, I can predict with confidence that Dallas has had a warmer fall than usual with temperatures failing to fall below freezing. I checked a history of Dallas weather, and I was almost right. The temperatures had fallen below freezing only once (http://www.accuweather.com/en/us/dallas-tx/75201/november-weather/351194?monyr=11/1/2013). Ceratitis capitata, the model insect used in the study by Penarrubia-Maria, thus may exhibit slightly higher threshold temperatures than the insects in Dallas, Texas, but the general relationship of insects with cold temperatures seems to hold true.

My most notable encounter with an insect over break occurred when I observed a noticeably malnourished wasp crawling on a window in my house. I took this as an opportunity to add to my insect collection for the lab portion of this class, but unfortunately, I did not have a kill jar at my disposal. So I was forced to make a makeshift kill jar:

Makeshift Kill Jar

This particular wasp, I believe, is a polistine paper wasp. Because food resources are particularly scarce for wasps once late November and December roll around, it was not surprising that this wasp was visibly low in energy, as it exhibited little ‘fight’ once caught.

Paper Wasp

On Thanksgiving Day, I was playing outside with my cousins when one of them noticed a cool looking bug crawling on the side of the house. I rushed on over to examine it, and noticed that it was in fact a true bug (order Hemiptera, suborder Heteroptera), and recognized it as a stink bug. I did not agitate this bug to test this hypothesis, but from my experience I believe it to be the case (it is always possible that it was a mimic). It is generally safe to assume that if you live in a wooded area, you have run across stink bugs at some point. It is just as safe to assume that if you have run across a stink bug and have made the mistake of picking it up (since it is pretty cool looking after all), you can imagine the horrible smell as you are reading this. The potent odor is something not quickly forgotten, so I decided to do a little research about it.

I was mainly curious about the odor’s components, when it’s released by the bugs, and its effectiveness in warding off predators. Luckily, it did not take me long to find a paper that addressed exactly those three topics (although it discussed a different species of stink bug than the one I found in my cousins’ backyard). A study published in the Journal of Chemical Ecology tested a variety of aspects of the chemical defenses of the stink bug Cosmopepla bimaculata through a range of methods, some of which were rather…unorthodox (like sticking the bugs on their tongues, for instance).

Chemical Composition

Using the paper mentioned above as well as a section from the Encyclopeda of Entomology, I found that the components of the chemical odor consisted primarily of long chain alkanes, aldehydes, and esters (which is to be expected as esters especially are the primary components of many odors).

Some of the organic compounds found in stink bug secretions. Source: Encyclopedia of Entomology

Since what I remembered of stink bug odor reminded me of the classic smell of a skunk, I did some research into the chemical composition of skunk odor to see if there were any common components. I was surprised to find that, at least according to this paper that studied the components of spotted skunk spray, stink bug secretions and skunk spray do not share any chemical components. Rather, the skunk spray contains primarily sulfurous compounds as opposed to esters. The evolutionary significance of this difference would be an interesting topic for further study.

When is the odor released?

The original paper I cited from the Journal of Chemical Ecology had some interesting findings relative to when the stink bugs actually use their chemical defense. Firstly, it seems that they are more reluctant to use it than one might think. Generally, when provoked by prodding, the bugs will simply walk in the other direction or try other evasive techniques rather than secrete their foul odor. The experimenters found that it was not until actually picked up that the bugs secreted a significant amount of the odor. Perhaps this is due to the energetic costs of secreting the odor, or even the detrimental effect of secreting the odor too often and actually attracting predators. It would be interesting to research the various pressures affecting this behavior.

Additionally, the researchers found that while undisturbed females generally did not secrete any pheromones, 3 of the 4 undisturbed males did secrete one of the compounds. It is possible that this is evidence of the use of sex pheromones similar to the ones studied in an experiment conducted by Ho and Millar. In their experiment, Ho and Millar found male stink bugs to be the sole sex pheromone producers and suggest that this may be due to the benefit in having males signal to females once they have found a good habitat for mating or  because the shorter average lifespan of males makes the risk of actually attracting predators amount to a smaller cost than it would be for the females.

Success in Deterring Predators

As I alluded to earlier, the experimenters in the first experiment  tested the effects of the chemical secretions on potential predators both by examining the behaviors of various birds and lizards as well as by tasting the bugs themselves. All of the birds and lizards that were tested by being given the choice of stink bugs or control prey (either crickets or houseflies) exhibited an aversion to eating the stink bugs which demonstrated the success of the chemical defense method of preventing predation. Not only would they spit out or run away from the bug that was currently emitting the odor, but they oftentimes would also avoid any subsequent stink bugs that were placed in the cage. In either an act of dedication to their field or sheer madness, the experimenters actually placed the stink bugs on their tongue and even chewed them in order to ascertain the exact sensation that would be experienced by a predator. Doing so caused an “instantaneous burning sensation and chemical taste that lingered for up to 20 minutes…followed by a slight localized numbness of the tongue, which lasted 1-2 hours.” Not only does the stink bug produce an stench and unpleasant taste, but it also causes prolonged pain in the mouth of its predators.

Given the effectiveness of this defense, it is interesting that it is not employed by more prey. Determining the costs of producing chemical defenses would be an interesting future study.