Exploring Nutrient Availability and Herbivorous Insect Population
Dynamics Across Multiple Scales
Abstract
Nutrient composition varies greatly across landscapes, influencing the
spatiotemporal variation and dynamics of populations, yet few studies
have investigated this pattern across multiple scales. We tested how
nutrient limitation affects herbivore populations, from individual
behavior to landscape-level population dynamics, using the Australian
plague locust, Chortoicetes terminifera (Walker), with field populations
and long-term survey data from across their range. At the individual
level, juvenile locusts selected for a carbohydrate-biased intake target
of 1 protein (p) to 2 carbohydrate (c), and exhibited the highest growth
and shortest development time when fed artificial diets with that same
1p:2c ratio during the final juvenile instar. At the field level,
locusts kept in cages with protein-biased plants redressed their
nutritional imbalance by selecting carbohydrate-biased diets (up to a
1p:20c ratio) for over a week after being removed from the
protein-biased environment, returning to the 1p:2c intake target once
the deficiency was met. At the landscape level, locust outbreaks were
negatively correlated with soil nitrogen and showed a non-linear
relationship with soil phosphorus, peaking at approximately 4% soil
phosphorus. We disentangled the interaction between mean annual
precipitation and soil nitrogen using comprehensive locust surveys and
remotely sensed soil and weather data spanning decades. This study is
the first to integrate lab, field, and remote sensing approaches,
demonstrating the importance of nutrient balancing and acquisition
across scales for herbivores. Specifically for locusts, we show that
low-nitrogen environments promote outbreaks, likely by reducing plant
protein-to-carbohydrate ratios. Incorporating soil quality data into
locust plague forecasting models could help improve prediction accuracy.