Sarcomere formation and longitudinal growth in the developing flight muscles of Calliphora

New sarcomere formation and length changes in sarcomeres have been investigated in the sixth dorsal longitudinal flight muscles in puparia and newly-emerged adults of Calliphora vomitoria. The hypotheses are investigated that new sarcomeres are formed during a period of rapid longitudinal growth by either Z band division or by serial addition at the ends of the muscles. At about 3 days and 9 hr after puparium formation, when the muscles are just beginning their longitudinal growth, the Z bands in existing sarcomeres appear to divide throughout the muscles. Calculations indicate that the number of sarcomeres quadruple. By 3 days and 15 hr the final number of sarcomeres is formed. Thereafter length increases in the sarcomeres account for length increases in the muscles. Sarcomere lengthening can account for a 26% increase in muscle length over the course of adult emergence. [¹⁴C] Leucine incorporation into proteins is equally distributed throughout the muscles at 3 days and 9 hr supporting the hypothesis that the new sarcomeres are formed throughout the muscles. [¹⁴C] Adenosine similarly shows no concentration of incorporation. Guide cells at the ends of the muscles appear to be pulling on the muscles. It is suggested that the tension from the guide cells is inducing the Z band division and the length increases of the sarcomeres. If the guide cells are cut, the muscles collapse and no longer increase in length.     

Reproductive status and flight activity of the overwintered Colorado potato beetle

Mating behavior of post-diapause Colorado potato beetles, Leptinotarsa decemlineata (Say), was observed within an overwintering site, a rotated potato field, newly colonized potato plants, and under laboratory conditions. The influence of spring mating on beetle flight in the presence and in the absence of host plants was investigated using a computer-linked flight mill system. Diapause was terminated simultaneously in male and female beetles, and the first matings were observed as early as within the first 24 h after the beetles emerged from the soil (60–90 DD accumulated). The beetles mated within the overwintering site, the potato field, and the fields rotated out of potatoes. Mating status did not affect flight behavior of overwintered beetles; however, unfed beetles displayed higher flight activity than fed beetles. Most flight activity took place soon after flight muscle regeneration, and then declined sharply by the 5th day after flight initiation. Mating in or near overwintering sites soon after diapause termination might be an important factor in providing gene flow between insecticide-resistant and insecticide-susceptible Colorado potato beetle populations, and should be considered in designing resistance management plans.     

Energy substrates for flight in the Colorado beetle,Leptinotarsa decemlineata Say

Colorado beetles could be induced to fly when suspended on a roundabout. The group which showed the greatest tendency to fly when suspended and flew for the longest period were females 10–12 days after diapause break. Flights lasted for 20–30 min and were occasionally longer. No change in haemolymph carbohydrate levels occurred during flight but significant increases in haemolymph total lipid levels and significant decreases in haemolymph proline levels were observed. ¹⁴C-proline injected into the haemolymph was utilised very rapidly in flown insects but disappeared only slowly in non-flown insects.     

Synthesis of mitochondrial protein in the flight muscles of the Colorado beetle. Differentiation in vivo between extra- and intra-mitochondrial contributions to the amino acid incorporation into mitochondrial protein

By using cycloheximide, an inhibitor of cytoplasmic protein synthesis, conditions were investigated to estimate in vivo the extra- and intra-mitochondrial contributions to the synthesis of organelle protein in the flight muscles of Colorado beetles. With 4-day-old beetles about 15% of the [(14)C]leucine incorporation into mitochondrial protein is resistant to the action of cycloheximide. The incorporation into cytosol protein is inhibited by more than 99.5% with cycloheximide. During the first hour after precursor administration the incorporation into mitochondrial protein proceeds, in both the presence and the absence of cycloheximide, at a more-or-less linear rate with time. The cycloheximide-resistant amino acid incorporation is sensitive to the inhibitor of mitochondrial protein synthesis, chloramphenicol. The uncertainties inherent in the use of cycloheximide were discussed in arriving at the conclusion that about 15% of the mitochondrial protein is formed inside the organelle.     

Fusion of myocytes with larval muscle remnants during flight muscle development in the Colorado beetle

The transformation of the slow contracting larval m. obliquus lateralis caudalis II during metamorphosis into the asynchronous indirect flight muscle, m. obliquus lateralis dorsalis, in the Colorado beetle, Leptinotarsa decemlineata, was examined by electron microscopy. Particular attention was paid to the fate of the larval muscle fibres, the origin and behaviour of the myoblasts for flight muscle development and the change of the myofibrillar filament lattice of the larva into that of the adult. In the pre-pupal period, the larval muscles dedifferentiate and fragment. At pupation, the muscle fibres consist of cell fragments containing very few myofibrils. The sarcoplasmic reticulum and the transverse tubular system are greatly reduced. The number of myoblasts developed from satellite cells by mitosis increases considerably. They penetrate the muscle fibre and surround the cell fragments. The new fibres of the flight muscle develop from myocytes fused with the larval fragments. The larval basal lamina, surrounding the cell fragments and myoblasts, is present in pupae up to 1 day old. In pupae about 2.5 days old new myofibrils appear that have the adult filament lattice. The insect muscle transformation and the repair of vertebrate muscle after injury show striking resemblances.     

Amino acid metabolism during flight in the Colorado potato beetle, Leptinotarsa decemlineata

The highest capacity for flight was demonstrated in males reared in long day conditions. During flight there is a significant decrease in proline content and to a lesser extent in glutamate. At the same time alanine accumulates, but its accumulation does not show stoichiometry with the decline in proline and glutamate during the first minutes of flight. This failure in stoichiometry suggests that glutamate dehydrogenase plays an important role in the early phases of flight.     

Ultrastructure of juvenile hormone-induced degenerating flight muscles in a bark beetle,Ips paraconfusus

Summary Topical application of 5 g of a juvenile hormone analogue (JHA), ZR-615, to female callow adults of Ips paraconfusus induced degeneration of the dorsoventral flight muscles. Within 24h after JHA-treatment the diameter of the myofibrils was reduced to almost half due to the lysis of the peripheral myofilaments. Mitochondria showed conspicuous degenerative changes like swelling, dissolution of the matrix or presence in the matrix of dense filamentous material or myelin-like figures. Degeneration of the mitochondria seemed to take place inside isolation membranes derived from sarcoplasmic reticulum. A number of granular osmiophilic bodies appeared in the sarcoplasm. Three days after JHA-treatment the muscles were very thin and sheath-like. Most of the mitochondria had already degenerated. The dense sarcoplasm contained numerous crystalline bodies. The granular dense bodies were also more frequent. The myofibrils were comprised of only occasional small bundles of myofilaments. The tubules of the T system enclosed an amorphous material. The nuclei and the tracheal system remained intact but they were crowded due to the decreased volume of the muscle. In some specimens degeneration of the myofibrils and mitochondria was completed by the third day. No sign of degeneration was observed in the flight muscles of acetone treated control insects.Supported by the National Research Council of Canada grant A4669.We thank Dr. G.B. Staal, Zoecon Corp., Palo Alto, California, for the generous gift of ZR 615, and Messrs A. Syed and M. Horta for rearing the insects     

Mode of formation of the flight muscles in a butterfly Pieris brassicae

The formation and development of the dorsal longitudinal flight muscles of the butterfly Pieris brassicae L have been studied by electron and light microscopy. These imaginal muscles arise from two symmetrical pairs of mesothoracic larval muscles, which are morphologically indistinguishable from the other wall muscles at the beginning of the 5th larval instar. However, 2 days before the end of this instar an accumulation of myoblasts is observed at the median region of these muscle fibres. The muscle fibres are penetrated by the myoblasts and broken into fragments. Progressive dedifferentiation of the larval fibrillar material in each of the muscle fragments is observed during the first days of the pupal development. The myoblasts within the basal lamina of the original larval muscle fibres remain associated with the muscle fragments. Myoblasts then fuse with the larval muscle fragments, which simultaneously fuse with each other. This results in the formation of rudimentary imaginal muscle fibres. The development of these fibres, particularly myofibrillogenesis, is studied until the emergence of the imago.     

Effect of diet and feeding history on flight of Colorado potato beetle, Leptinotarsa decemlineata

We evaluated the hypothesis that Colorado potato beetle (Leptinotarsa decemlineata Say) (CPB) flight frequency is related to diet, and that it changes with duration of food unavailability or exposure to poor quality food by exposing adult overwintered and summer CPB populations to an acceptable host plant (conventional foliage), a poor host (insect resistant transgenic foliage expressing Bacillus thuringiensis tenebrionis[Btt] Cry3a toxin) and no host. Exposure to poor host and no host treatments (with or without water) decreased mean daily flight frequencies and the overall number of overwintered CPB flying, but increased the mean daily flight frequency and number of summer population CPB that flew. Overwintered CPB did not react to an absence of plants at emergence whereas summer CPB increased mean daily flight frequencies when plants and water were not available. The flight response to insect resistant foliage was similar to that for starvation treatments in both populations indicating that flight may not be triggered by Btt toxins but by starvation brought on by feeding on poor quality food. Flight was observed in all treatments for the duration of the test with two exceptions; overwintered beetles fed insect resistant foliage ceased flying after day 17 and summer beetles starved without water ceased after day 8 of a 29‐day study.     

Mitochondrial changes in flight muscles of normal and flightless Drosophila melanogaster with age

Fine structural changes in mitochondrial morphology pertaining to size, number and growth were examined in flight muscles of normal and experimentally dewinged male Drosphila melanogaster ranging up to 26 days of age. In the normal winged flies, the number of mitochondria decreases during the first week of adult life whereas the size of individual mitochondrial profile increases significantly. Changes in mitochondrial size and number are due to the fusion of mitochondria. Fused mitochondria are extremely large in size and irregular in shape. In 26-day old normal flies, the number of mitochondria increases while the mitochondrial size is reduced indicating mitochondrial division. In comparison to the normal flies, dewinged flies exhibit a similar degree of mitochondrial fusion and growth during the first week of life. However, the extent of mitochondrial fission in 26-day old dewinged flies is greater than in the normal flies of this age. Structural mechanisms of mitochondrial fusion and fission are described. The objective of this study was to examine the relative effects of age and flight activity on the mitochondria.     

Taste receptors in Colorado beetle larvae

Electrophysiological studies show that at least six sensilla on the various mouthparts of larval Colorado potato beetles (Leptinotarsa decemlineata) contain chemosensory cells. These sensilla are found on the galea, maxillary palps, and labial palps. Sodium chloride, sucrose, some amino acids, and chlorogenic acid are among the effective stimuli. The sensitivity spectrum of these cells correlates with known larval phagostimulants.     

Enzyme systems of insecticide detoxication in the Colorado beetle

The activity of three enzymatic systems of xenobiotic metabolism (cytochrome P-450-dependent monooxygenases, non-specific esterases and glutathione S-transferases) was studied at different stages of development of the Colorado potato beetle (Leptinotarsa decemlineata). Significant sex and ontogenetic differences in the content of cytochrome P-450, position of maxima of CO-difference spectra of the cytochrome P-450 reduced form and substrate specificity of cytochrome P-450 were revealed. The activity of non-specific esterases was shown to increase depending on the age of larvae. The insecticide 1-naphtholenol methylcarbamate which is metabolized by the system of cytochrome P-450-dependent monooxygenases is more toxic in the larvae than at the imago stage, which is correlated with the activity of this system at different stages of ontogenesis. The microsomal monooxygenase inhibitor, piperonylbutoxide, increases the insecticide toxicity in the Colorado beetle imago more than 2-fold. The experimental results testify to different contribution of the detoxication systems to the sensitivity of the Colorado beetle to insecticides at various metamorphosis stages.     

Development of the indirect flight muscles of Drosophila.

We have followed the pupal development of the indirect flight muscles (IFMs) of Drosophila melanogaster. At the onset of metamorphosis larval muscles start to histolyze, with the exception of a specific set of thoracic muscles. Myoblasts surround these persisting larval muscles and begin the formation of one group of adult indirect flight muscles, the dorsal longitudinal muscles. We show that the other group of indirect flight muscles, the dorsoventral muscles, develops simultaneously but without the use of larval templates. By morphological criteria and by patterns of specific gene expression, our experiments define events in IFM development.     

Mitochondria in the flight muscles of insects. III. Mitochondrial cytochrome c in relation to the aging and wing beat frequency of flies

1. In the present study a correlation has been sought between aging, flight muscle mitochrondria (sarcosomes), cytochrome c, and flight ability in the blowfly, Phormia regina. 2. During the 1st week of adult life, individual sarcosomes increase in mass from 2.7 x 10^–7 µg. dry weight at the time of emergence, to 8.5 x 10^–7 µg. by the 7th day. During this period of growth, the number of sarcosomes per fly (6.7 x 10⁸) remains constant. When mature, the sarcosomes account for 32.6 per cent of the total muscle dry weight, or close to 40 per cent on a wet weight basis. 3. It appears probable that the high content of flight muscle cytochromes is entirely localized in the sarcosomes. The cytochromes continue to be synthesized and increase in titer within the sarcosomes for 7 days after adult emergence. 4. As determined spectroscopically, the various cytochrome components at all times maintain a constant ratio both to one another and to the sarcosomal dry weight. This suggests the possibility that the cytochrome system may be synthesized as a single entity. 5. The wing-beat frequency of Drosophila funebris and Phormia varies with the age of these flies, being lowest at the time of emergence and maximum after the 6th day. 6. The relations between wing-beat frequency, respiration during flight, and sarcosomal cytochrome c content are discussed. On the basis of some likely assumptions it is calculated that the cytrochrome c turnover number is over 5,000, and that the cytochrome c turns over once for every two wing-beat cycles.     

Quiescence in the Colorado potato beetle, Leptinotarsa decemlineata

Quiescence (death feigning) was induced in the Colorado potato beetle, Leptinotarsa decemlineata by mechanical disturbance of live and artificial plants on which beetles were walking, feeding or grooming. The response consisted of a sudden cessation of activity lasting 12 to 500 s. Recovery from this immobile state was usually preceded by either antennal or leg movement. The time taken for beetles to come out of the immobile state (i.e. recovery time) was not dependent on age or sex of beetles or on stimulus duration, but was dependent on degree of displacement and on satiation level. Repeated stimulations led to longer recovery times and to a smaller proportion of responding beetles. Stimulation within the immobile state also prolonged recovery time. The most effective frequency of mechanical disturbance for startling beetles was 30 Hz. This response is presumed to be part of the extensive defense repertoire of this beetle, but we have so far been unable to discover a natural enemy that will elicit it.