Strong alignment between individuals and attraction to trophic resource in patchy landscapes favour group foraging in locusts nymphs

Collective foraging is one aspect of the gregarious lifestyle that can bring advantages to group members. Spatial and temporal food distribution plays a key role among the factors that give gregarious collective foraging or individual foraging an advantage. Locusts are particularly interesting model species to study the differences between these two alternative foraging strategies, because of their ability to switch from a so-called “solitarious” phase to a “gregarious” phase, depending on population density. In this paper, we studied the impact of spatial resource distribution and inter-individual interactions on the foraging success of locusts. We developed an agent-based model to explore for which landscape types and collective motion characteristics gregarious marching band have an advantage over solitarious individuals. We performed a calibration on our model, with a pattern-oriented modelling approach, to explore which individual movement parameter values provide realistic displacements at group level. Then, we studied the impact of spatial distribution of vegetation on the foraging success of isolated or groups of locust nymphs, and show that the success of a band depends on the aggregation of the vegetation within the landscape in which it moves, but also on certain characteristics of group movement, such as the strength of the alignment of individuals and the attraction towards vegetation. Patchy environment and a high alignment within the band favoured gregarious groups. These results match the type of landscapes that also favour the switch of behaviour from solitarious to gregarious in locusts.