Insect flight muscle: maturation and senescence.
That holometabolous insects undergo a number of post-emergent morphological, physiological, and biochemical maturational processes, termed metachemogenesis, is unquestionable. This is readily evident as regards the capacity for flight. The maturational processes demonstrated in mitochondria and/or mitochondrial enzyme systems, myofibrils, as well as other biochemical systems have been sufficiently documented in a number of species, directly correlated with the attainment of optimal flight ability in terms of both wing beat frequency and the duration of sustained flight; suggesting that the phenomena is a general one, particularly in the orders Diptera and Hymenoptera. Subsequent to the time-dependent maturational processes which are species-specific, there is an observed relatively stable period of flight performance during adult life. With advancing age, flight performance declines, most noticeably in the duration of sustained flight. This diminution, as the maturation of flight ability, is also correlated with a decline in a number of biochemical parameters, i.e. levels of and/or ability to utilize glycogen, various enzyme systems, mitochondrial efficiency, particularly in dipteran insects. Furthermore, as the morphological degenerative changes observed in aging flight muscle are variable and do not appear to be of sufficient magnitude to account for the substantial decline in the physiological expression of flight, one may assume that neurophysiological and/or biochemical mechanisms are responsible. A more fundamental question as regards the mechanisms of agins is whether or not the decrease in flight performance with advancing age is due to random error, or is in some way genetically controlled as the post-emergent maturational changes must be. The orderly sequential pattern of enzyme changes associated with the maturation and senescence of flight ability, particularly in the male housefly, and the demonstration of an identical sequential pattern of change in two of these enzymes, again correlated with the maturation and decline in flight performance in two other dipteran insects, suggest that the senescence of flight ability may also be manifested in an orderly programmed manner.