At rest, diffusion through the tracheal system supplies an insect with enough oxygen. Very active insects, such as flying locusts, bees and beetles, have flight muscles with a very high respiration rate. Diffusion alone cannot deliver oxygen quickly enough, so these insects have extra adaptations.1. Withdrawal of tracheal fluid
During intense activity the flight muscles respire partly anaerobically, producing lactate. Lactate is soluble and lowers the water potential of the muscle cells. Water moves by osmosis out of the ends of the tracheoles into the muscle cells. This draws air further down the tracheoles, so more of the tracheole surface holds air rather than fluid. Oxygen diffuses much faster through air than through liquid, and the surface area available for exchange increases, so oxygen reaches the muscles faster.2. Ventilation by pumping
Many large active insects ventilate the tracheal system. Muscles contract and relax to squeeze and expand the abdomen (and sometimes the thorax), pumping air in and out by mass flow. Flight movements themselves also compress the thorax. In locusts, spiracles open and close in sequence so that air enters through the front spiracles and leaves through the rear ones, giving a one-way flow.3. Air sacs
Some tracheae widen into air sacs, which act as reservoirs of air and increase the volume of air moved with each pumping movement.These mechanisms maintain steep concentration gradients and shorten the distance gases must diffuse through liquid, meeting the high oxygen demand of flight.
During intense activity the flight muscles respire partly anaerobically, producing lactate. Lactate is soluble and lowers the water potential of the muscle cells. Water moves by osmosis out of the ends of the tracheoles into the muscle cells. This draws air further down the tracheoles, so more of the tracheole surface holds air rather than fluid. Oxygen diffuses much faster through air than through liquid, and the surface area available for exchange increases, so oxygen reaches the muscles faster.2. Ventilation by pumping
Many large active insects ventilate the tracheal system. Muscles contract and relax to squeeze and expand the abdomen (and sometimes the thorax), pumping air in and out by mass flow. Flight movements themselves also compress the thorax. In locusts, spiracles open and close in sequence so that air enters through the front spiracles and leaves through the rear ones, giving a one-way flow.3. Air sacs
Some tracheae widen into air sacs, which act as reservoirs of air and increase the volume of air moved with each pumping movement.These mechanisms maintain steep concentration gradients and shorten the distance gases must diffuse through liquid, meeting the high oxygen demand of flight.