A STRUCTURAL AND BIOCHEMICAL-STUDY ON THE EFFECTS OF METHOPRENE ON FLIGHT-MUSCLE DEVELOPMENT IN LOCUSTA-MIGRATORIA L

The effects of methoprene, a juvenile hormone analogue, on the development of the dorsal longitudinal flight muscles in Locusta migratoria migratoriodes (R and F) were investigated. Fifth-instar larvae (12 +/- 12 h) were topically treated with 475-mu-g of methoprene and flight muscles were subsequently removed for ultrastructural study at regular intervals until the 8th day of adult life. Treatment with methoprene slightly shortened the length of the fifth stadium, markedly reduced normal developmental increases in the cross-sectional area of muscle fibres, inhibited the formation of interfibrillar tracheoles within muscle fibres and caused profound changes in muscle fibre fine structure. The fine-structural differentiation of muscle fibres from treated insects was greatly accelerated compared with that of controls, being more or less complete by the 7th day of the fifth instar. Thereafter, into early adult life, musclefibre structure became progressively more disorganized. Methoprene treatment of fifth-instar larvae also significantly reduced the respiratory control of flight muscle mitochondria extracted from such insects on their becoming 10-day-old adults. The effects of methoprene upon flight muscle developmental processes are discussed.