Experimental Studies on Locomotor Activitiy in Locusta migratoria migratorioides, R & F

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Abstract
(1) A technique was devised for determining quantitatively the “ spontaneous ” locomotor activity of hoppers of Locusta migratoria migratorioides in terms of the distance travelled in half an hour in a special activity cage in which temperature, light intensity and humidity could be accurately controlled and all stimulation avoided.(2) All the material used was derived from the same stock, and was kept under very constant and accurately known conditions from the time of hatching.(3) The activity as measured in this way showed extremely great variation, as would be expected from our knowledge of the periodic character of “ spontaneous ” activity in many animals.(4) Distribution curves were plotted showing the frequency with which various levels of activity were reached, and these curves were used as a basis for comparing the amount of activity shown under different conditions. In all these curves the mode was at the origin; by far the greater portion of the activity was of a very low order, though high activity occurred occasionally. The hoppers showed about 70 per cent, of their activity in the lowest activity group (0–5 cm./min.). The percentage fell very rapidly to the next group (14 per cent.), and then gradually to the 30–35 cm./min. group (0·6 per cent.), beyond which the records did not go.(5) Hoppers kept throughout development in a very dry atmosphere showed a lower activity than hoppers kept in a very moist atmosphere.(6) Differences in the relative humidity of the atmosphere in the activity cage had very little effect on activity. The figures obtained suggested, but did not prove, the following:—(a) First and second instar hoppers were more active in a wet than in a dry atmosphere.(b) Hoppers of instars 3–5 showed the greater activity in the humidity which represented a change from that at which they had been kept during development: those reared dry showed greater activity in a moist atmosphere: those reared wet in a dry atmosphere.(7) The figures suggested that males were more active than females.(8) Broadly speaking, all the various instars travelled the same distance in the same time. A consideration of the facts relating to size in the various instars led to the conclusion that the younger instars must have a higher rate of automatic nervous discharge than the older instars.(9) Jumps were hardly ever encountered at a light intensity of 3–4 ft.-cands., though quite a number were obtained at about 20 ft.-cands. These jumps were “ spontaneous.”(10) The underlying causes of activity are discussed. It is concluded that external stimulation was by far the most potent factor in influencing the amount of activity exhibited, and that it was the crucial factor in the production of the gregarious phase, but that(11) Previous environmental conditions, especially previous conditions of stimulation, modified both spontaneous and reflex activity by influencing the nervous excitability of the insect; and(12) Certain “ determining ” stimuli in the present environment affected the form, intensity and threshold of reflex, and, to a lesser extent, of spontaneous activity.

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