Anti-Locust Bulletin (1959) 33, 1-51

R.F. Chapman (1959)
Field observations on the behaviour of hoppers of the Red Locust (Nomadacris septemfasciata Serville)
Anti-Locust Bulletin 33, 1-51
Abstract: Observations were made on the nymphal (hopper) stages of the Red Locust in the Rukwa Valley, Tanganyika, during the period 1954-1956. Hoppers were present during the rainy season from January to March. More rain was recorded in the 1955-56 season than in the previous two, but relative humidities were consistently high at all times, with dew deposited at night. The range of temperatures during January was about 10°C. compared with 16°C. in August. The lowest maximum temperatures were recorded in January when only about half the amount of sunshine was recorded as compared with September (9 hours per day). In the rainy season the winds were rather variable.
The highest population studied was that of 1955, but no marked differences in the size of C (width of head) were recorded during the period of these observations. In 1956, hoppers in bands were nearer gregaria in coloration than were isolated individuals but this difference was not observed in 1954. The adults resulting from these hopper populations were phase transiens with a slight shift towards solitaria in 1956. Hopper development took 6 to 10 weeks, the earlier instars developing more rapidly than the later ones. The rate of development varied in different habitats, being quicker in areas dominated by the grass Echinochloa than elsewhere.
Hoppers roosted overnight in tall grass, ascending to the tops in the morning at first light. The movement was initiated by increasing light intensity, being upward because of the previous `head-up' orientation of the hoppers. The evening ascent was related to a steep fall in temperature. At other times of day ascent was induced by rising or falling temperature or by auditory stimulation. Climbing resulting in the avoidance of excessively high temperatures near the ground was also seen. Morning descent was produced by a sharp rise in temperature, the movement being directed by visual stimuli, possibly food. At other times descents were caused by high winds and rain.
Orientation to the sun varied under different conditions. Flanking was usual in the early morning and late evening, and the facing position during the heat of the day. The change-over from flanking to facing occurred at about 30°C. (air temperature). Locusts moved round the grass stems in the course of the day as the sun moved across the sky. Under sunny conditions hoppers frequently showed a preference for the lee sides of stems. Flanking locusts were hotter than facing or backing locusts and those on the lee sides of stems were hotter than those exposed to the wind. Orientation was also partly to light.
The adults of Nomadacris scatter before oviposition (Scheepers and Gunn, 1958) so that the egg-pods that gave rise to the hoppers studied were widely distributed. The hoppers themselves tended to scatter on hatching. As the Echinochloa became taller, the hoppers concentrated in it, later tending to disperse again through lack of mutual visibility. Migration was seen between 25°C. and 32°C.; it was more active at the higher temperatures of this range but inhibited above them. Hoppers progressed by leaping from stem to stem, maintaining a constant orientation. All the hoppers were similarly orientated. Orientation was not related to the lie of the grass, and the direction of band movement was also independent of this, being generally downwind and mainly northwards on warm days and southwards on cool days. Bands did not cover very great distances and probably only spent about 10 per cent of the suitable time in migrating. Hoppers were more active in bands than when solitary.
Feeding occurred mainly in the morning and evening. It was reduced at low temperatures but only doubtfully so at high temperatures. No difference in feeding between the sexes was observed, but newly moulted hoppers contained less food. At first, feeding was restricted to Cyperus but later Echinochloa provided most of the evening feed.
Activities were considered to be triggered-off by changes in stimulation, absolute levels of stimulating factors providing a background which merely limits the level of activity. The Rukwa habitat was considered to favour concentration but not aggregation, to which attention should be paid for an understanding of the origin of outbreaks.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)

Research topic(s) for pests/diseases/weeds:
environment - cropping system/rotation
population dynamics/ epidemiology

---

Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Nomadacris septemfasciata