Oikos (1955) 6, 124-148

H.O. Backlund (1955)
Red Locusts and vegetation
Oikos 6 (2), 124-148
Abstract: The distribution of the Red Locust in its invasion and outbreak areas is considered, and an attempt made to find causes for its uneveness. Except as stray individuals, which are rare, permanent populations are restricted to the relatively small outbreak areas. Although northern and southern limits of invasions may be determined by macroclimatic factors, these are not otherwise regarded as important. Microclimate however greatly influences locust distribution within the permanently inhabited areas, as does the vegetation. The relationship between these is examined for the various stages in the locust's life history, since every stage has its own ecological preferences. Throughout, it is obvious that the locust's requirements are met by the mosaic vegetation typical of outbreak areas and are favoured by grass fires. The macroclimate is effective in that it produces a kind of adult diapause, and egg laying starts simultaneously in the whole outbreak area. Maturation, which occurs just prior to the rains, seems to be linked with ingestion of water, perhaps as dew. Bare patches in the vicinity of tall grass are preferred egg-laying sites; the choice of open soil appears to be due to preference for light, and of tall grasses for roosting. Larger bare areas such as those produced by fires are not favoured. Time and duration of rains in relation to soil type affect egg laying and hatching. Heavy clays when softened sufficiently are preferable to light soils because the hard surface crust developing in dry weather protects the eggs against drought. Development of young vegetation and hatching are simultaneous, making shelter and food immediately available for young hoppers. The hoppers become adult in the dry season, and the mosaic vegetation provides food and the varied microclimate required by adults for basking and roosting. Behaviour now varies with the macro-climate and the physiological state of the locust. Fliers move to tall grass stands and probably feed in their lower layers and shelter near the ground. Diurnal movements of locusts are correlated with the microclimate created by the plant species, in particular Echinochloa pyramidalis, which is most frequented by adults although it is not specially preferred as food. Concentrations of hoppers are favoured by the lie of grasses over which they move, while adult concentrations arise on the downwind edges of tall vegetation as a result of short flights down-wind. Any disturbances increase such flights, as do grass fires, which latter also decrease available areas of vegetation. Since grassland is preferred by locusts, they tend to concentrate on the edges of woodland, where swarmlets arise.
(The abstract is excluded from the Creative Commons licence and has been copied from Acridological Abstracts with permission by NRI, Univ. of Greenwich at Medway.)

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