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Why are insects so energy-efficient while flying? Is it because of their light weight and aerodynamics or due to very efficient biochemical transformations (food->energy)?

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Your question is very vague. Energy efficient compared to what? What makes you think they are 'so' energy efficient? You should try to explain why you're asking the question, as in its current state is has no context. –  Richard Smith-Unna Jul 21 '12 at 22:19
    
-1: please improve your question by better specifying what you are comparing insects to (birds? planes? or...?) –  nico Jul 22 '12 at 9:29
    
In my original question I was asking insect energy efficiency compared to human made battery operated flying devices but some super users closed my question claiming that it should belong in a separate topic other than biology... –  Adolfo Perez Jul 22 '12 at 13:10
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@AdolfoPerez that's because the answer to the original question is about the limitations of battery technology and nanoscale aeronautical engineering, not about biology :). Unfortunately the engineering SE is still at the definition stage. –  Richard Smith-Unna Jul 23 '12 at 14:12
    
@RichardSmith Now I wonder what happens when a question like mine touches different fields of knowledge? In this case bio-engineering or biological engineering. Biology knowledge applied to engineering solutions. We can't be so black and white. –  Adolfo Perez Jul 23 '12 at 17:57

2 Answers 2

up vote 12 down vote accepted

Insect flight muscle is capable of achieving the highest metabolic rate of all animal tissues, and this tissue may be considered an exquisite example of biochemical adaptation.

Locusts, for example, may (almost instantaneously) increase their oxygen consumption up to 70-fold when starting to fly. In humans, excercise can increase O2 consumption a maximum of 20-fold, and for birds in flight the figure is about 10-fold (Wegener, 1996; Sacktor, 1976).

As Wegener (1996) has put it (in his definitive paper):

The aerobic scope (the ratio of maximal to basal rate of respiration) of insects is unrivalled in the animal kingdom

Flight is powered by ATP hydrolysis, and these impressive metabolic rates are achieved by very effective control of ATP hydrolysis and regeneration.

  • Metabolism is aerobic, thus allowing for much more efficient ATP production from hexoses (as compared with, say, anaerobic metabolism).
  • Flight muscle may account for up to 20% of body mass.
  • In insects, haemoglobin and myoglobin are absent. Instead, gaseous O2 is transported to the tissues by a system of tubules and deposited so close to the site of consumption that (seemingly) it may reach mitochondria by diffusion.
  • Locusts fuel flight by burning sugars in the early stages, gradually changing to use lipids as fuel. (In bees, flight is totally fuelled by hexose consumption). This is achieved by effective control of glycogen breakdown and glycolysis, by modifying the activity glycogen phosphorylase (glycogen breakdown) and phosphofructokinase (PFK), a key control enzyme of glycolysis.
  • There is an enormous literature on these topics, but suffice it to say, in the case of glycolysis, control is very efficiently achieved by allosteric regulation of PKF, where fructose 1,6-bisphosphate and fructose 2,6-bisphosphate play key roles (see Sacktor, 1976).
  • This allosteric control very effectively allows glycolysis to be (almost instantaneously) turned on and operate at a maximum value, and to be (almost instantaneously) turned off.

References

Wegener, G. (1996) Flying insects: model systems exercise physiology Experientia May 15;52(5):404-12. (See here)

Sacktor B. (1976) Biochemical adaptations for flight in the insect. Biochem Soc Symp. 1976;(41):111-31. (See here)

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Your detailed answer is very enlightening @TomD. There is so much to learn from nature and it is an extremely difficult challenge trying to imitate nature's efficiency when building our own flying devices. No battery ever created is as efficient as insects natural way of powering their flight given their size –  Adolfo Perez Jul 22 '12 at 13:29

The smaller an animal is the easier it becomes for it to fly. That is because surface area increases to the second power of the diameter of the animal whereas mass increases to the third. So the larger a thing is the more mass per surface are it has.

And since insects tend to be small they tend to be good at flying.

As for any other reason, I don't think insects are any more energy efficient than say, birds.

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Logical, but can you provide any references for this? It would strengthen your answer significantly. –  LanceLafontaine Aug 11 '12 at 4:28
    
Well it's just the square-cube law: en.wikipedia.org/wiki/Square-cube_law. –  Hermann Ingjaldsson Oct 2 '12 at 17:28
    
True, but this isn't quite a complete answer. With reduced size, one compromises other areas that may benefit flight, such as wingspan (first thing that come to mind). Thus, being smaller doesn't absolutely equate to more efficient flying. –  LanceLafontaine Oct 2 '12 at 18:39
    
According to the square-cube law the wingspan decreases with size but the mass decreases even more. Which means flying requires less push-up force per surface area for smaller animals. –  Hermann Ingjaldsson Oct 3 '12 at 16:49

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