Anisotropic interaction and motion states of locusts in a hopper band

Swarming locusts present a quintessential example of animal collective motion. Juvenile locusts march and hop across the ground in coordinated groups called hopper bands. Composed of up to millions of insects, hopper bands exhibit coordinated motion and various collective structures. These groups are well-documented in the field, but the individual insects themselves are typically studied in much smaller groups in laboratory experiments. We present the first trajectory data that detail the movement of individual locusts within a hopper band in a natural setting. Using automated video tracking, we derive our data from footage of four distinct hopper bands of the Australian plague locust, Chortoicetes terminifera. We reconstruct nearly twenty-thousand individual trajectories composed of over 3.3 million locust positions. We classify these data into three motion states: stationary, walking, and hopping. Distributions of relative neighbor positions reveal anisotropies that depend on motion state. Stationary locusts have high-density areas distributed around them apparently at random. Walking locusts have a low-density area in front of them. Hopping locusts have low-density areas in front and behind them. Our results suggest novel interactions, namely that locusts change their motion to avoid colliding with neighbors in front of them.

Publisher Correction: Daily mapping of Australian Plague Locust abundance

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Daily mapping of Australian Plague Locust abundance

Locust population outbreaks have been a longstanding problem for Australian agriculture. Since its inception in the mid-1970s, The Australian Plague Locust Commission (APLC) is responsible for monitoring, forecasting and controlling populations of several locust pest species across inland eastern Australia (ca. two million km2). Ground surveys are typically targeted according to prevailing environmental conditions. However, due to the sheer size of the region and limited resources, such surveys remain sparse. Here we develop daily time-step statistical models of populations of Chortoicetes terminifera (Australian plague locust) that can used to predict abundances when observations are lacking, plus uncertainties. We firstly identified key environmental covariates of locust abundance, then examined their relationship with C. terminifera populations by interpreting the responses of Generalized Additive Models (GAM). We also illustrate how estimates of C. terminifera abundance plus uncertainties can be visualized across the region. Our results support earlier studies, specifically, populations peak in grasslands with high productivity, and decline rapidly under very hot and dry conditions. We also identified new relationships, specifically, a strong positive effect of vapour pressure and sunlight, and a negative effect of soil sand content on C. terminifera abundance. Our modelling tool may assist future APLC management and surveillance effort.

The role of the foregut in digestion in the cricket Teleogryllus commodus and the locust Chortoicetes terminifera

The role of the foregut (crop and proventriculus) in mechanical processing of food has received little attention in insects. Using the Australian plague locust (Chortoicetes terminifera) and the black field cricket (Teleogryllus commodus) as models, the role of the crop in processing of wheat or rye grass was examined. Interior cuticular structures (spines) of the foregut were described using light and scanning electron microscopy, with locusts having sclerotised structures and crops of crickets being unsclerotised internally. Muscular bands on the exterior surface of the crop part of the foregut are similar in males of both species, but contractions and movements are more forceful in locusts. Passage rate from the foregut is much faster in locusts (<3 h) than in crickets (>3 h). Water within the crop is reduced compared with the water content of fresh grass within the foregut of locusts, but water is increased in cricket crops. Spines within the crops are small relative to the size of food particles in both species. Some spines of locusts contain metals. The slower passage rate from the crop of crickets may be limited by the proventriculus. Foregut structure and food processing facilitates the generalist diet of crickets, but may restrict locusts to consuming softer grasses.