The Development of the Locust Jumping Mechanism : I. Allometric Growth and its Effect on Jumping Performance

Abstract

ABSTRACT The jump range of locusts of all instars varies throughout an instar, reaching a peak at apolysis in hoppers, and about 3 weeks after the final moult in adults. Mature adult locusts have an escape jump range three times that of young hoppers. During a period of repeated jumping, mature adults have an average jump range three times that of the hoppers. Allometric growth of the metathoracic leg occurs during development, and accounts for 25 % of the increase in range between the fourth instar and adult, the remaining increment being due to absolute size increase. The allometric changes do not, however, affect the mechanics of the femoro-tibial joint. The extensor apodeme to tarsus lever ratio remains at 27:1 in the fourth, fifth and adult stages. The extension of the joint would be expected to follow a similar pattern in the fourth instar and adult stages. The change in form of the metathoracic leg of the locust also means that the adult femur accommodates more muscle, i.e. 6·3 % of the total body weight in the adult male, as opposed to 4·3 % in the fourth instar male. Therefore relatively more force and energy may be available for use in a jump. The lengthening of the semilunar processes may be expected to have an effect on the energy storage capacity of the leg. In an escape jump, all instars use the same specific power output, which is more than the published figures for maximum specific power output (250Wkg-1, Weis-Fogh & Alexander, 1977, and 860Wkg-1, Pennycuick & Parker, 1966). This suggest that energy storage is necessary in locust hoppers.