Meeting Abstract
How physiological and ecological factors determine species’ population levels across space and time remains a fundamental question in organismal biology. One important area that has received little attention is the role of plant macronutrient availability in determining the success or failure of invasive and sporadically outbreaking species, such as many insect pests, despite the fact that macronutrient balancing has emerged as a key factor regulating animal feeding behavior and performance. Here, we took advantage of the first significant population upsurge of the South American locust, S. cancellata, in 60 years. Since 2016 large swarms left their small permanent breeding zone in NW Argentina and invaded Bolivia and Paraguay, as well as an expanded area throughout Argentina. Our field experiments show that wild S. cancellata strongly prefer carbohydrate over protein food options, suggesting that these locusts tend to be carbohydrate limited in contrast to the nitrogen limitation hypothesis. Our lab experiments showed that this species self-selected a highly carbohydrate-biased diet when given the option to balance protein and carbohydrate with synthetic diets – a ratio of 1:2 protein:carbohydrate. However, in both Argentina and Bolivia, we found that relatively few plants can provide this protein:carbohydrate ratio. These patterns are consistent with the observed preference for carbohydrate in the field and with our hypothesis that obtaining sufficient carbohydrates is a key, limiting nutrient for these locusts in their permanent breeding zone, and particularly under range expansion.
