Abstract
We studied the development of the indirect flight muscles and reproductive organs in long-winged (macropterous) adults of the flightless bug Pyrrhocoris apterus (L.) and the factors involved in flight muscles histolysis by means of total protein analysis. Both the extirpation of the corpus allatum, an endocrine gland that is the sole source of juvenile hormone, and sham operation accelerated histolysis and decreased the level of the total protein content of the flight muscles to the same extent. Degeneration of flight muscles was not a result of allatectomy but rather a consequence of injury, followed by resumption of enhanced food intake, because it was stimulated also by the removal of wings. Transfer of penultimate instar larvae to a diapause-inducing short-day photoperiod did not prevent imaginal growth and histolysis of flight muscles, but inhibited growth of ovaries in females and maturation of accessory glands in adult males. Thus inactivation of the corpus allatum in diapausing macropters does not prevent imaginal growth of their flight muscles. Application of a high dose of methoprene to the surface of intact long-day macropterous adults induced precocious histolysis of flight muscles and growth of ovaries in females and accessory glands in males. Prolonged starvation of macropterous adults had only a small effect on the histolysis of their flight muscles. The results indicate that imaginal growth and histolysis of indirect flight muscles in macropterous individuals of P. apterus are largely juvenile hormone-independent processes that are programmed to occur spontaneously, but can be affected by various internal and external factors.
Highlights
The possession of wings and ability to disperse by flight are important features of insects and have played a key role in their evolutionary success (Roff & Fairbairn, 1991; Kingsolver & Koehl, 1994)
De-alation of macropterous males and females accelerated the histolysis of the dorsolongitudinal flight muscles (DFM), which was accompanied by a substantial decrease in their total protein content and increase in that in the ovaries and accessory glands (Fig. 1A, B)
The macropterous adults were starved from the day of adult emergence and the total protein in their DFM determined on day 21 of their adult life
Summary
The possession of wings and ability to disperse by flight are important features of insects and have played a key role in their evolutionary success (Roff & Fairbairn, 1991; Kingsolver & Koehl, 1994). Wing polymorphism is a common phenomenon in insects and is the most commonly studied type of dispersal polymorphism and the focus of many reviews (Harrison, 1980; Dingle, 1985; Pener, 1985; Roff, 1990; Rankin & Burchsted, 1992; Zera & Denno, 1997). Flight muscles are usually reduced in the flightless morph (Smith, 1964; Marden, 2000) and muscle reduction is thought to be more important than wing reduction in elevating the fecundity of the flightless morph (Zera & Denno, 1997). Reduction of flight muscles may result from arrested development or from degeneration of originally functional muscles, and is not restricted to short-winged (brachypterous) morphs, since many long-winged (macropterous) species are polymorphic for flight muscle development (Harrison, 1980; Zera & Denno, 1997)
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