The "Ear" of a Praying Mantis

Hi everyone!

It's common knowledge that insects make sounds; many species in the Order Orthoptera (crickets, grasshoppers, katydids, and weta) make a "chirping" sound come twilight, and Madagascar hissing cockroaches (Gromphadorhina portentosa) creates a hissing sound which it's named after. Cicadas vibrate their bodies to emit a rather ear-piercing racket in which, some books say, can even break the human ear drum! While the insect world is alive with sounds, has anyone ever thought about whether or not insects can hear?

While I was searching for material through various entomology journals, I came across an interesting article  done in 1986 which tested whether or not praying mantis (Order Mantodea) can hear. Written by David D. Yager and Ronald R. Hoy, it looked at the (currently non-existing) Order Dictyoptera, which included mantises, cockroaches, and termites (Since then, this Order has been split up into Mantodea and two suborders of Blattodea--roaches and termites). There are other insect groups which have been reported to have hearing capacity, including the Orthoptera mentioned earlier. Moths (Order: Lepidoptera) can also hear, due to a tympanal organ located on their thorax.

Anyway, the study did some research on a praying mantis species, Mantis religiosa, the European Mantis, and found that there is a tympanal organ located in the ventral midline. As said in the paper, mantises are, indeed, an "auditory cyclops."

Picture 1: Between the second set of legs
 (the metathoracic legs) is the location of the cycloptic ear on a
 praying mantis.

The study used seven males and six females for their research. Researchers used a wide variety of stimulation over a broad range of frequencies to see how the M. religiosa would react. Essentially, mantises can hear the best in the ultrasonic range: 25 to 45 kHz. To compare, I found on Wikipedia.com that humans can only hear 20 Hz to 20 kHz; that is still less than what the M. religiosa can pick up! This "ear" is structurally similar to what one would find on many moth species, lacewings (Order: Neuroptera), and part of a cricket's auditory system. Unfortunately, the tympanal organ does not help with where a sound comes from, just that it exists.

Through some experiments with the mantises, it was found that by covering the ventral area of the insect with melted wax, specifically over a deep, narrow groove found in the midline (between the metathoracic legs), it lost the ability to hear. This midline structure was, therefore, proven as a key part in the tympanal organ's success.

Another really interesting thing about this study was by disecting the mantis "ear", scientists found that it was made up of two tympana that were facing each other. separated by less than 150 micrometers. Since the organs face each other, and are located rather close to one another, this provides an explanation as to why mantises couldn't perceive direction with sounds during the tests.

Picture 2: Do praying mantises "pray"?

So, what's the point of this? Why has a mantis developed a single "ear"? Well, scientists aren't entirely sure (at the point of this study--remember, 1986!), but they did think of something interesting. Since some mantis species fly around looking for mates at night, their hearing can be used as a warning system. Moths, lacewings, and crickets use their hearing as a way of detecting a bat's sonar while flying. Preliminary research has shown that an Asian species of mantis from the Hymenopodidae family will dramatically change its flight pattern upon detecting bat-like ultrasound pulses. Cool, eh?

Well, I never really thought about insect hearing capacity until this point. That clearly does make sense, doesn't it?! What do you guys think?

~Mel







You can find the study at:
http://www.mantislab.com/380.pdf (scroll down a bit--it's towards the middle)

Picture 1:
http://farm4.static.flickr.com/3034/2558924463_aee9d72e23.jpg

Picture 2:
http://farm1.static.flickr.com/132/346799957_3705f17781.jpg

Honey Bee Behavior...oh wait, I mean "Behaviour".

An interesting study that I found recently was all about Honey Bees (Apis spp). "Genetic Diversity in Honey Bee Colonies Enhances Productivity and Fitness", written by Heather R. Mattila and Thomas D. Seeley in 2007, looks at how genetic diversity within a hive can alter the overall togetherness of a colony.

Initially, it was thought that, within socialising species of insects, like the bees, wasps, and ants (basically, anything that is of the Order Hymenoptera), colonies will be more unified and work more efficiently if the individuals are all related to each other, a.k.a. a lack of genetic diversity. However, there is an interesting phenomenon noted by scientists as of late: polyandry is a reoccuring phenomenon among socialising insects. Polyandry, where one reproductive female (the queen) mates with two or more reproductive males (called drones), causes a lack of relatedness of the other females (called workers; they're infertile) within the colony.

Now, we've all heard of swarming, right? Swarming is when the queen and several thousand of her workers relocate to a new nesting site. This, however, is extremely risky: the study mentions how, once relocated, only 20% of colonies actually survives in its first year! This is due to workers not gathering enough resources for the colony, and they starve to death come winter-time. These known facts gave the researchers something to work with. They wanted to see how colonies which are genetically diverse (polyandry colonies) compare to uniformly genetic colonies when a swarming event occurs.

21 colonies were used for this experiment, with 12 of them having a queen that was inseminated with sperm from a unique set of 15 drones. The remainding 9 colonies were inseminated with sperm from a single drone. The honey bees were then relocated to a new nest site, simulating what would happen if a swarming event occured, and measurements of comb construction, brood rearing, foraging activity, food storage, population size, and overall weight gain were the comparisons between the two groups.

RESULTS TIME!!!

Interestingly enough, colonies which were more genetically diverse were much better off than colonies that were more related to each other. The polyandric bees were able to construct about 30% more comb than the other group within a two week period (after the "swarming" event). In addition, foraging levels were also significantly greater with the genetically diverse colonies: in the two weeks after the relocation, the diverse colonies had gathered about 39% more stored food than the uniform colonies. When honey was starting to be produced between the two groups of colonies, guess which group was about twice as heavy as the other? Yup, the polyandric bee colonies!

What about new workers that are being produced? Well, the genetically diverse colonies got that one covered too! The production of new workers in genetically uniform colonies were clearly outmatched by genetically diverse colonies within the first month after the swarming event. The brood rearing was increasing continually (until the end of August, which is Autum in the Northern Hemisphere), whereas the genetically uniform colonies were producing low numbers of workers over the same period of time. Due to this, there were many more workers in the genetically diverse versus the genetically uniform colonies: with an average of 26,700 (± 1830) individuals in comparison to 5,300 (± 2,400) individuals, there really is no comparison!

It's pretty interesting that genetically diverse colonies can work better together and produce more fit colonies than genetically uniform ones. We've all heard that each worker is a "sister" to the other workers in a hive, and while in many cases it's correct, we should start calling them "half-sisters"! I guess having multiple gene lines in one colony would be beneficial in multiple ways; a disease ploughing through honey bees can be slowed down or even stopped if there are variations between each individual.  I'm now curious as to the proportion of bee colonies (and ant and wasp colonies) are polyandric in the wild in comparison to genetically uniform colonies. Perhaps this can help the issue of declining Apis spp.  around the world? More research would have to be done before that statement is valid!

Thanks!

~Mel

PS: Forgive me if I wrote in American, my Kiwi friends! I tried!

Picture from: http://www.nmhoney.com/nmhoney/Sub%20Files/Pictures/Bee%20Swarm%20in%20Apple%20tree-orchard.jpg

You can find the study at:
http://www.sciencemag.org/content/317/5836/362.full 

Global Climate Change and the Effect it has on Plant-Insect Relations

Hi everyone!

A report, written by Peter Wilf and Conrad C. Labandeira, looks at "global warming" and its effects on plant-insect relationships. Combined, insects and terrestrial plants make up the majority of Earth's current biodiversity, and taking into account that around half of the total discovered species of insects today are herbivorous, this is definitely what caught my eye. Currently, we're going through some abrupt climate change due to excess amounts of greenhouse gasses (Carbon Dioxide, Methane, etc.) that are being released into the atmosphere on a day to day basis. While the whole world is worrying over how to slow or even stop the process, this isn't the first time Earth has gone through a change in temperature. In the past, periods of warming (what we know as "global warming") and cooling (also known as an"ice age") happened well before Homo sapiens walked the land.

While it's true that the changing temperatures are cyclic, to observe what has happened in past periods of time will give scientists a gage as to what will happen in the future. The report focuses on insect and plant relations. For this report, Wolf and Labandeira observed how the climatic differences affected species diversity among plants and insects during the late Paleocene to the early Eocene. During this time, global warming was occuring; an increase of average temperature was gaged at 6°C from the Paleocene to the Eocene (14.4° to 21.3°, respectively). Looking at fossil evidence from Wyoming, USA, scientists were able to figure out the results.

After identifying 41 different types of insect damage on 39 Paleocene and 49 Eocene species of flowering plants, the evidence showed that the damage was more significant in the Eocene than in the Paleocene. This means that an increase in herbivory (eating vegetation) happened when there were warmer temperatures. In addition, insects ate more of a variety of plants in the Eocene than in the Paleocene.

One thing that was really interesting about this was the observation of certain tree species. Trees in the Betulaceae family (which includes common day Birches) were fairly common during both the Paleocene and the Eocene time periods. Two specific species of Betulaceae, Alnus spp. (Eocene) and Corylites spp. (Paleocene) were extremely common throughout both landscapes. Since Betulaceae plants are the favorite food of many insects, the two species were looked at during these two times to also compare rates of damage from insects. Scientists found that the Betulaceae species found in the Eocene period were attacked more than during the Paleocene.

So, what can we expect from this? Will bug herbivory increase and cause more destruction in our future as our current world becomes warmer and warmer? Most likely. It would be interesting to observe plant/insect relationships from the past 50 years and compare them to today. In addition, I'm curious about Betulaceae and how they are being affected with the recent global warming trends; are they also being attacked more due to increases in global temperature? It would be interesting to look more into this!

~Mel

Study ca be found at: http://www.sciencemag.org/content/284/5423/2153.full.pdf?sid=8193f9ef-e38a-4b19-aea3-7646237feb4a