Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2004
Publication Date: 10/15/2004
Citation: Sword, G.A., Babah, M. 2004. Linking locust gregarization to local resource distribution patterns across a large spatial scale. Environmental Entomology. 33(6):1577-1583. Interpretive Summary: As local population densities increase, the underlying pattern of resource distribution can play a critical role in either promoting or deterring locust gregarization and subsequent swarm formation. As a result, it is thought that knowledge of the spatial distribution of resources could be very important for locust management by aiding in the identification of habitats that are likely to promote locust gregarization. In light of the known association between local patterns of resource distribution and locust gregarization, the spatial distributions of 2 perennial tussock grasses, Panicum turgidum Forsk. and Aristida pungens Desf. (sometimes referred to as Stipagrostis pungens)(Poaceae) were compared between 2 regions of Mauritanian that differ in their historical frequencies of locust gregarization. Specifically, the hypothesis tested was that the distribution of grass tufts should be more aggregated and therefore more likely to promote locust phase change in the high frequency gregarization area. This study demonstrated that resources known to play a role in locust gregarization tend to be aggregated to a greater extent in a region of the Mauritanian plague recession area where locust gregarization frequently occurs. This finding provides evidence across a large area in support of the notion that local resource aggregation can promote locust gregarization. These results provide insight into the means by which large-scale patterns of locust gregarization may be attributed to the behavior of individuals expressed in the context of their local environments. Incorporating an understanding of local ecological processes into preventative management strategies can lead to more precise survey and control operations in locust afflicted countries. The benefits of applying such an approach include a reduction in financial costs, pesticide use, and potentially harmful effects on the environment.
Technical Abstract: Spatial resource distribution patterns play an important role in mediating density-dependent phase change (gregarization) in locusts. The degree of contagion or aggregation of resources in a habitat can increase the probability of locust gregarization by increasing the frequency of contact among individual locusts. The spatial distribution patterns of 2 resources upon which gregarization can occur, the tussock grasses Aristida pungens and Panicum turgidum (Poaceae), were examined in 2 adjacent regions of the desert locust (Schistocerca gregaria Forskål) plague recession area in Mauritania that differ in their historical frequencies of locust gregarization. The hypothesis that the distribution of grass tufts should be more aggregated and thus more likely to promote locust phase change in the high frequency gregarization area was tested. Grass tufts were more abundant and both species were larger in the high frequency gregarization area. The spatial distribution patterns of tufts in both areas were largely aggregated at the 200-2000m2 scale. As predicted, the degree of aggregation was more extreme across the high frequency gregarization area. This study provides large-scale support for the predicted association between individual behavior, local resource distribution, and locust gregarization. The observed differences in grass abundance and size between the high and low frequency gregarization areas suggest that factors such as topography or hydrology may underlie differences in plant distribution and contribute to locust gregarization in the high frequency area.