Some Factors affecting Breeding and Oviposition of the Red Locust, Nomadacris septemfasciata (Serv.)

• Published in: Bulletin of entomological research 1959-08, Vol.50 (2), p.333-353
• Main Authors: Symmons, P., Carnegie, A. J. M.
• Format: Article
• Language: English
• Subjects: Research Paper
• ISSN: 0007-4853; 1475-2670
• DOI: 10.1017/S0007485300054614

Observations were made on the red locust, Nomadacris septemfasciata (Serv.), between October 1957 and February 1958 in an area of grassland, six miles long by one mile wide, marked out by beacons and divided lengthwise by a line of beacons down the centre, in the Rukwa Valley of south-west Tanganyika. One half of the plot had been burnt off completely in the latter part of the dry season; the other half was unburnt and carried in part a four-year accumulation of growth and in part an area of standing grass that had regenerated after a damaging fire during the previous wet season and then, for the most part, flooded. Vegetation profiles were made along the whole length of the plot, and rain gauges, soil thermometers and soil tensiometers were installed at regular intervals along the three lines of beacons. Assessments of the population and distribution of adult locusts within the plot were made from Land-Rover or on foot in mid-October, mid-December (ten days after the onset of the rains) and early in January. A systematic search was made for egg-pods, starting at the end of December, along furrows ploughed down the middle of each of a number of narrow strips mown in the grass in sets near each beacon and sampling equally the burnt and unburnt halves of the plot. The first hoppers were seen on 3rd January, and assessments of hopper populations were carried out four times during January. The primary object of the work was to study the effect on choice of oviposition site and on incubation success of the type and condition of the grassland (whether burnt during the previous dry season, at an earlier date, or left unburnt) and its possible bearing on control of the species in an outbreak area. Data were also obtained on the conditions of air temperature, soil moisture, soil temperature and rainfall in which eggs are laid and incubated; and the effect of variations in these factors on oviposition and on incubation success was examined. It was observed that, in the hot, dry conditions of mid-October, adult locusts were completely absent, from the recently burnt-over ground, and were found almost exclusively in that part of the standing grass that had suffered a wet-season burn. By mid-December, the locusts had spread out from the unburnt into the burnt-over zone, where the grass had put out fresh growth, but many were still to be found hi the former, with a concentration along the line of contact with the latter. By early January, the size of the population had