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Dr. Scott Kirkton, Union College - Understanding the Molting Process of Grasshoppers


Studying how insects metabolize and process oxygen could bring some relief for farmers hoping to protect their crops without using dangerous pesticides.

Dr. Scott Kirkton of Union College is learning a great deal about the biochemistry that triggers a grasshopper's molting process.

Dr. Scott Kirkton is an associate professor of biology at Union College. He earned his doctorate degree in biology at Arizona State University where his dissertation project focused on effects of insect body size on metabolism and locomotory performance. He then went on to the University of California, San Diego for his postdoctoral training in mammalian respiratory and exercise physiology. His current research focus is on how insect development and body size alters the biochemistry, morphology, physiology and biomechanics of oxygen delivery, muscle performance and locomotion

More about grasshopper molting process

Dr. Scott Kirkton - Understanding the Molting Process of Grasshoppers

With over one million known species, insects are the most evolutionarily successful group on the planet.  If one gathered up all the species on the planet, plants, fungi, bacteria, protozoa, invertebrate animals and vertebrate animals, insects would make up 54 percent of all these species.  With the exception of the open ocean, insects are found everywhere on Earth.

One major reason for insects’ amazing diversity is their unique air-filled tracheal respiratory system.  Oxygen enters the tracheal system through openings along the body and is then transported to the tissues via a network of branching air-filled tubes.  While seemingly bizarre to us, this tracheal system allows insects to have the highest per gram oxygen consumption rate of any animal.  In other words, their metabolic rates per gram can be over 12 times higher than a world-class athlete. 

Even with this amazing respiratory system, we have found that insects may have problems with oxygen delivery during development.  For example, juvenile grasshoppers go through six developmental molts before becoming adults.  At each molt, grasshoppers shed their skin-like exoskeleton and become larger.  Between molting periods, grasshopper body mass doubles; however, the stiff exoskeleton prevents the individual from increasing in size.

We discovered that during the seven-day period between molts, grasshopper jumping endurance decreased significantly, which suggests that they might have problems with oxygen delivery.  Using the Advanced Photon Source – a powerful synchrotron X-ray at Argonne National Laboratory outside Chicago, we visualized the inside of a living insect.  We saw that the increase in mass between molts was compressing the air-filled tracheal system and reducing the grasshoppers’ ability to breathe, which resulted in a lower jumping performance.  We hypothesize that a reduction in oxygen delivery to the tissues is the cue to activate the hormones necessary to begin molting. 

Our findings could be applicable to a wide-range of insects and therefore may benefit farmers.  For example, to reduce the impact of crop pests, we suggest storing grains at low oxygen levels.  Lower ambient oxygen levels would reduce the metabolic rate of the insects and should induce molting thereby speeding up their development time to adulthood.

A faster development time would produce smaller adults with reduced appetites and shorter overall life spans. And that could be good news for farmers looking for a chemical free way to protect their plants.

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