Download Assessing the Entomological Accuracy of MSNBC news article “Fruit

Assessing the Entomological Accuracy
of MSNBC news article “Fruit flies: Nature’s hovercraft”
Scientific Literature: The Aerodynamics of Free-Flight Maneuvers in Drosophila
Dr. Houseman
BIO3323
Feb 14, 2005
Introduction (with credentials of entomological authority)
The MSNBC online article, Fruit Flies: Nature’s Hovercraft by Daniel Kane, is poorly written
from an entomological perspective because it lack depth and precision. Ultimately, the significance of
the scientific findings is difficult to comprehend. The article was compared to the original scientific
literature, “The Aerodynamics of Free-Flight Maneuvers in Drosophila”, and other credible sources to
see whether the popular press has given justice to the scientific discoveries.
The authors of the original scientific literature are Steven N. Fry, Rosalyn Sayaman, and
Michael H. Dickinson. Dr. Fry is an accomplished entomologist who does research at the Institute of
Neuroinformatics at the University of Zurich. His research is concerned with the analysis of
aerodynamic forces produced during free flight saccades in Drosophila (Fry, 2005). Rosalyn Sayaman
has worked in the Dickinson lab since 2000, working on the free flight aerodynamics of Drosophila
(Dickinson, 2005). Dr. Dickinson is a professor of Bioengineering at the California Insitute of
Technology. He has numerous entomological publications in the field of flight and his ultimate goal is
to construct a true robotic fly (Dickinson 2005).
The main scientific findings resulting from the scientific study are: inertia of the fly’s body as
the fly turns is more difficult to overcome than friction of the viscous air, and tiny changes in wing
motion generate the torque required to create the quick saccades observed (Fry et al, 2003).
Experimental Specimen
Although Daniel Kane mentions the main discovery of the paper, he never mentions the species
of fly that was used under experimentation. The fly is Drosophila melanogaster, belonging to the order
Diptera (Fry et al, 2003). This fly has been a model organism for biologists and geneticists for a very
long time (Dickinson, 2003). Kane states that the results can be applied to most insects, however, one
should not overlook the importance of D. melanogaster in this experiment. It is true that inertia, not
friction, dominates the flight dynamics of insects and this is applicable to most insects. However, the
experiment cannot be replicated with an insect from any taxonomic order. The entire experiment,
observations, and calculations are based on the analysis of saccades, the quick ninety-degree turns
characteristic of the Diptera (Fry et al, 2003). Although this is a single study, the ultimate goal for Fry
and his colleagues is to reverse engineer an insect, and they chose D. melanogaster because they are
among the most advanced insects in terms of flight. They have many specializations for flight such as:
fast visual systems, powerful muscles, wings capable of generating unsteady aerodynamic forces, and
contain specialized halteres capable of sensing rotations (Dickinson, 2003). In this context, D.
melanogaster is a specialist and will provide the most relevant information.
Wing Kinematics
Kane makes a slight error stating the following: “in fruit flies, the topside of the wing faces up
during the downstroke, but then the wing rotates on its axis so that the underside faces up during the
upstroke.” Firstly, the method of wing stroke he attempts to explain is characteristic of all insects, not
just fruit flies (Ramoser et al, 1998). Secondly, Kane doesn’t explain the wing beat pattern effectively.
A better way of stating the above is as follows: in insects, the wing pronation occurs dorsally as the
wing transitions from upstroke to downstroke, and supination occurs ventrally when the wing
transitions from downstroke to upstroke (Sane, 2003). The stroke traces a figure eight pattern.
(Ramoser et al, 1998). Stroke angle, angular deviation, and angle of attack are fundamental properties
required to understand the intricate detail of wing behaviour, particularly in the analysis of quick
saccades. These properties, friction, inertia, and other wing modifications in flight cannot be
interpreted until the general wing movement pattern is understood.
Moreover, Kane merely mentions that slight changes in wing motion are responsible for
generating the torque, however, he doesn’t go in any depth in how this is related to acceleration, the
driving mechanism to overcome inertia (Fry et al, 2003). How do the wing movements differ during
the saccade? At the beginning of the saccade, the outside wing tilts back and beats with a greater stroke
amplitude to increase velocity relative to the inside wing (Fry et al, 2003). A deceleration and
subsequent counter-torque is experienced at approximately 12.5ms resulting from increased amplitude
and stroke plane angle of the inner wing (Fry et al, 2003). Again, Kane makes a significant point, but
he provides no elaboration. Slight changes in wing behaviour is one of the significant findings of the
paper; the facts are mentioned over and over again and even represented in Figure 3C, demonstrating
the direct relationship between torque and wing kinematics (Fry et al, 2003). Kane’s simplistic
overview and lack of detail does not do justice to this unique discovery.
Kane effectively shows how insect aerodynamics is a relatively new science, but he lacks depth in
his explanation. Airplanes have a wing shape that creates a lower pressure above the wing; pressure
and its relationship to distance of air travel above and below the wing creates lift. A fly, on the other
hand, has wings that constantly flap. The wings move mainly side to side; not up and down (Dickinson,
2001). The importance of the new discoveries should be stated clearly and concisely; they lay down a
foundation for advancement in the field of insect flight. This is emphasized when Kane uses the
following insight from Dickinson in the article: this research provides just the beginning! (Kane, 2003).
Experimental Design
Kane correctly mentions most of the important components of the experimental design
including the infrared video cameras, robot fly, and even the robot’s “mineral oil” habitat (Fry et al,
2003). But he doesn’t explain the importance of the yaw axis of rotation. In fact, Kane never even
mentions the axis of rotation under observation and leaves the reader interpreting which 90 degree
rotation is the saccade related to. Is it horizontal (rolling)? Vertical (yaw)? Or both? (Benson, 2004).
Kane does, however, correctly summarize the importance of “Bride of Robo fly” in this experiment.
The robot was used to reenact the fruit fly in its own environment in slow motion to identify the
aerodynamic forces which are inherent during wing motion (Dickinson, 2001).
Inertia versus friction
Kane never mentions the significance of frictional resistance of the air’s viscosity during torque
about the yaw axis. Although friction is not the major force to overcome, it plays a strong role because
insects are generally small and affected by fluid dynamics and associated low Reynold’s numbers
(Dickinson et al, 1999). The experimenters looked at the relationship between the moment of inertia
and a frictional dampening coefficient (I/C) to see their importance relative to one another (Fry et al,
2003). From figure 1C, it is evident that angular acceleration and deceleration are important throughout
the time course of the saccade, and angular velocity is less important than previously believed (Fry et
al, 2003). Although Kane does state that insects must exert a force to start turning and then exert a
counter force to stop turning, this was never an issue of debate. It is the relationship between friction
and inertia that is important; which one is more difficult to overcome? He completely overlooks the
existence of a relationship between friction and inertia during a saccade (Fry et al, 2003).
Sensory Systems
Although the article is lacking in depth in most areas, Kane does a good job of explaining the 2
sensory systems: the compound eyes and the mechano-sensory halteres (Sherman et al, 2003). Kane
correctly explains that halteres are single paired modified hind wings dominant during saccades. The
dynamic responses of the 2 systems differ in that the visually mediated response is stronger for slower
rotations, whereas, the haltere-mediated response is stronger for faster rotations along the 3 functional
axes (Sherman et al, 2003). However, Kane never mentions that halteres are unique to the order
Diptera (Fry et al, 2003). It is important for the reader to realize that the halteres are specialized
modifications, for specialized insects, which have created a specific mechanism to effectively
overcome inertia and mediate hovercraft-like locomotion. By leaving out little pieces of information,
Kane doesn’t do justice to the scientific data; to understand the science, one must be look into the
details and get specific. Kane overly simplifies the data to a point where the reader is left confused with
a “sketchy” understanding of the big picture and overall goal in mind.
Advancing Technology
Early in the article, Kane mentions the significance that the findings can have on human
technological development in aerodynamics. Kane effectively explains how mimicking the detail of
insect flight can be used to build robots that can ultimately be used in many fields such as: in
surveillance, search and rescue, and even planetary development (Dickinson, 2003). Kane often uses
quotes from Dickinson, the 3rd author, who explains how his team has used a systems analysis
approach to study flight and how this new discovery is merely the beginning of the project (Fry et al,
2003)! Using an expert, particularly one from the original scientific literature, makes the read more
credential. However, Kane doesn’t elaborate on the significance of Dickinson’s remarks . Before
tackling the experiment, Dickinson and his colleagues realized the importance of interrelating the
various organ systems (nervous, sensory, muscular, visual, etc) (Dickinson, 2003). As the fly moves
through space, it receives a stream of sensory information, and to understand flight meant not isolating
the flight system from its other related components (Dickinson, 2003). Therefore, the importance and
relevance of the study is that is lays down a crucial foundation from which other scientists can work
from; then ultimately reverse-engineer to build a hovercraft-like robot.
Final Remarks
From a journalistic standpoint, the title of the article, “Fruit flies: Nature’s hovercraft”, is
concise and “catchy”. Early on, Kane mentions the implications to human society; this is effective at
getting the reader’s attention. Humans are inherently selfish and want to know how the study can
benefit themselves. Kane neglects the species name and its importance to the experiment to simplify
the article so that it appeals to the casual reader. Ultimately, he creates more work for the reader; the
reader has to use alternative sources to comprehend the science behind the story. Furthermore, Kane
merely states the major findings from the scientific literature. His lack of precision and explanation
creates confusion as many facts are left for interpretation.
References
Benson T. 2004. Aircraft Rotations: Body Axes [online].
Available from [http://www.grc.nasa.gov/WWW/K-12/airplane/rotations.html]
Dickinson MH. 2001. Robofly: A documentary by Jason Spingarn-Koff [online].
Available from [http://journalism.berkeley.edu/projects/mm/spingarnkoff/flyorama/robofly.html]
Dickinson MH. 2003. Come Fly with Me. California Institute of Technology [online].
Available from [http://pr.caltech.edu/periodicals/EandS/articles/LXVI3/fly.html]
Dickinson MH. 2005. Dickinson Lab [online].
Available from [http://www.dickinson.caltech.edu/people_sayaman.html]
Dickinson MH., Lehmann FO, Sane SM. 1999. Wing Rotation and the Aerodynamic Basis of Insect
Flight. Science [online]. Available from
[http://www.physics.ohio-state.edu/~wilkins/writing/Assign/topics/fly/fly.html]
Fry. 2005. Steven Fry: Research [online]. Available from
[http://www.ini.unizh.ch/~steven/?loc=Research]
Fry SN, Sayaman R, Dickinson MH. 2003. The Aerodynamics of Free-Flight Maneuvers in
Drosophila. Science [online]. Available from
[http://proxy.bib.uottawa.ca:2065/itw/infomark/433/500/57990295w1/purl=rc1_EAIM_0_A100962723
&dyn=3!xrn_1_0_A100962723?sw_aep=otta77973]
Kane D, 2003. Fruit flies: Nature’s Hovercraft [online]. Available from
[http://www.msnbc.msn.com/id/3077426/]
Ramoser WS, Stoffolano JG. 1998. The Science of Entomology, Fourth Edition. Boston: WCB
McGraw- Hill.
Sane SP. 2003. The Aerodynamics of insect flight. The Journal of Experimental Biology [online].
Available from [http://jeb.biologists.org/cgi/content/full/206/23/4191]
Sherman A, Dickinson MH. 2003. A comparison of visual and haltere-mediated equilibrium reflexes in
the fruit fly Drosophila melanogaster. The Journal of experimental Biology [online].
Available from [http://jeb.biologists.org/cgi/content/full/206/2/295]