Theoretical rates of increase of gregarious and solitarious populations of the Desert Locust

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Abstract
Leslie matrices are used to compare theoretical populations of gregarious and solitarious Desert Locusts, Schistocerca gregaria (Forsk.). Despite their lower fecundity, the synchrony and faster maturation of gregarious populations permit them to have much faster rates of increase than solitarious populations. When realistic mortality estimates are assumed the differences can be very pronounced even when the rates of mortality are the same for both phases; this suggests that the longer period during which solitarious locusts are susceptible to predation is critical. The conclusions are briefly discussed with respect to the genesis and maintenance of locust plagues and the evolutionary significance of gregarisation.