Field Observations of the Sheltering Behavior of the Solitarious Phase of the Desert Locust, Schistocerca gregaria, with Particular Reference to Antipredator Strategies

Abstract

Solitarious phase locusts are cryptic animals and usually seek shelter in plants. This trait was thought to be a specific antipredator strategy associated with the solitarious phase. However, information on preferences for particular shelter plants and sheltering behavior remains limited. In the present study, small-scale field observations were conducted to investigate the sheltering behavior of the solitarious phase of the desert locust, Schistocerca gregaria, in relation to plant species and size. A spiny plant, Fagonia arabica, and two spineless plants, Nucularia perrini and Stipagrostis plumosa, were identified at the survey site. Although the size of F. arabica did not differ significantly from that of the two other plant species, almost all the solitarious locusts used F. arabica for shelter. Locusts were found on a majority (78%) of the individual F. arabica examined, but the number of sheltering locusts varied. The F. arabica plants with locusts were significantly larger than those without. A positive correlation was found between the total number of sheltered locusts (nymphs and adults) per individual plant and the plant size (m3). The same tendency was observed for nymphs and adults alike. The local densities (no. of sheltered locusts / plant size (m3)) remained constant over a range of plant sizes. These results might indicate that solitarious locusts selected their shelter plant based on its species and size. Because F. arabica is a spiny plant, we concluded that solitarious locusts use not only visual but also physical defense mechanisms as antipredator strategies. (Resume d'auteur)