Fine structure of degenerating and regenerating flight muscles in a bark beetle, Ips confusus: I. degeneration

The flight muscles of the bark beetle Ips confusus undergo a pronounced degeneration within 4 days of introducing beetles into the bark of pine logs. Numerous lysosomes develop between the myofibrils, and the fibrils become greatly reduced in size. In female beetles many of the mitochondria and most of the myofilaments disappear from the muscle, and apart from lysosomes, tracheoles and a few fine granules, little structural organization remains in the fibres. The muscles of males degenerate to a lesser extent and, unlike those of females, contain numerous lipid globules in the degenerating condition. The significance of flight muscle degeneration as a possible prerequisite for reproduction in females is discussed. In males, flight muscle degeneration may have behavioural significance in confining the flightless insect to the host tree for repetitive mating and gallery maintenance.