Using remotely sensed data and insect behavior to predict locust outbreaks

A long withstanding area of ecology is understanding the environmental drivers of animal population dynamics. One major driver is nutrient availability, with nitrogen (N) and phosphorus (P) often positively associated with population growth across trophic levels, but particularly for herbivores who are hypothesized to be limited by N and P. However, it is becoming increasingly apparent that not all herbivores follow this long held assumption. Here we investigate the relationship between a common outbreaking locust species, Australian plague locusts (Chortoicetes terminifera), and available nutrients using lab, field, and remote sensing approaches. We show that locusts prefer and have faster growth rates on carbohydrate biased diets as compared to protein biased diets, and when kept in field cages over protein-biased plant communities they over consume carbohydrates for more than a week. Using historical locust outbreak data and a database of soil nutrients for the Australian continent, we show that locust outbreaks are negatively correlated with soil nitrogen and non-linearly correlated with approximately 4% phosphorus. This suggests that a more nuanced approach of acknowledging an animal's life history must happen in order to predict how increasing nutrients drive animal populations. Lastly, these findings also suggest that taking nutrient quality into consideration can aid in forecasting locust (and other insect pest) outbreaks globally.