Meeting Abstract
33-7 09:30 - 09:45 Low nitrogen environments promote locust outbreaks across local to continental scales Cease, A*; Lawton, D; Learned, J; Toole, I; Thompson, N; Hales, C; Waters, C; Arizona State University, Tempe, AZ; North Carolina State University, Raleigh, NC; Mau Nui Seabird Recovery Project, Makawao, HI; NSW Department of Primary Industries, Trangie, NSW; Arizona State University, Tempe, AZ; Arizona State University, Tempe, AZ; NSW Department of Primary Industries, Dubbo, NSW acease@asu.edu https://sustainability-innovation.asu.edu/global-locust-initiative/people/
Nutrient availability across landscapes can greatly influence spatiotemporal variation of populations via nutritional effects on individuals, yet few studies have investigated these patterns from individuals to landscapes. Using field populations and long-term survey data from across their range, we tested the nitrogen limitation hypothesis for herbivores using Australian plague locusts (Chortoicetes terminifera). Juvenile locusts collected from marching bands in New South Wales self-selected a carbohydrate-biased diet of 1 protein (p):2 carbohydrate (c), and had the highest growth and shortest development time when fed artificial diets with that same 1p:2c ratio over the duration of the 5th (final) juvenile instar. Simultaneously, we ran field cage experiments. Fourth instar locusts were added to 1 m3 cages placed over pasture grasses that had one of three fertilization treatments: 0, 87.5, and 175 kg nitrogen/ha. Overall, the grasses remained protein biased, but protein content decreased in the control plots over the course of the experiment. Regardless, there were no significant differences in growth rate among treatments and locust survival was low across treatment groups (~30-40%). Living in the field cages substantially impacted locust nutritional status. Locusts re-collected from both the low and high fertilizer field cages consistently selected highly carb-biased diets over the course of 9 days, ending on about 1p:3c, and indicating that the grasses available in the field cages were quite protein-biased relative to their demands. Using decades of locust survey data from the Australian Plague Locust Commission and Australian soil maps, we found that outbreaks were most likely to occur on soils that had a low nitrogen mass fraction of about 0.05-0.08. Together, these data corroborate findings on other locust species suggesting that low nitrogen environments promote outbreaks by lowering plant protein to carbohydrate ratios.