Browsing by Autor "Jon F. Harrison"

Now showing 1 - 4 of 4

Climate change expected to improve digestive rate and trigger range expansion in outbreaking locusts
(Wiley, 2022) Jacob P. Youngblood; Arianne Cease; Stav Talal; Fernando Copa; Héctor E. Medina; Julio Rojas; Eduardo V. Trumper; Michael J. Angilletta; Jon F. Harrison
Abstract Global climate change will probably exacerbate crop losses from insect pests, reducing agricultural production, and threatening food security. To predict where crop losses will occur, scientists have mainly used correlative models of species' distributions, but such models are unreliable when extrapolated to future environments. To minimize extrapolation, we developed mechanistic and hybrid models that explicitly capture range‐limiting processes, and we explored how incorporating mechanisms altered the projected impacts of climate change for an agricultural pest, the South American locust ( Schistocerca cancellata ). Because locusts are generalist herbivores surrounded by food, their population growth may be limited by thermal effects on digestion more than food availability. To incorporate this mechanism into a distribution model, we measured the thermal effects on the consumption and defecation of field‐captured locusts and used these data to model energy gain in current and future climates. We then created hybrid models by using outputs of the mechanistic model as predictor variables in correlative models, estimating the potential distribution of gregarious outbreaking locusts based on multiple predictor sets, modeling algorithms, and climate scenarios. Based on the mechanistic model, locusts can assimilate relatively high amounts of energy throughout temperate and tropical South America; however, correlative and hybrid modeling revealed that most tropical areas are unsuitable for locusts. When estimating current distributions, the top‐ranked model was always the one fit with mechanistic predictors (i.e., the hybrid model). When projected to future climates, top‐ranked hybrid models projected range expansions that were 23%–30% points smaller than those projected by correlative models. Therefore, a combination of the correlative and mechanistic approaches bracketed the potential outcomes of climate change and enhanced confidence where model projections agreed. Because all models projected a poleward range expansion under climate change, agriculturists should consider enhanced monitoring and the management of locusts near the southern margin of the range.
Field bands of marching locust juveniles show carbohydrate, not protein, limitation
(Elsevier BV, 2023) Arianne Cease; Eduardo V. Trumper; Héctor E. Medina; Fernando Copa Bazán; Jorge Frana; Jon F. Harrison; N. Joaquín; Jennifer Learned; Mónica Roca; Julio Rojas
Locusts are grasshoppers that migrate <i>en masse</i> and devastate food security, yet little is known about the nutritional needs of marching bands in nature. While it has been hypothesized that protein limitation promotes locust marching behavior, migration is fueled by dietary carbohydrates. We studied South American Locust (<i>Schistocerca cancellata</i>) bands at eight sites across Argentina, Bolivia, and Paraguay. Bands ate most frequently from dishes containing carbohydrate artificial diets and minimally from balanced, protein, or control (vitamins and salts) dishes-indicating carbohydrate hunger. This hunger for carbohydrates is likely explained by the observation that local vegetation was generally protein-biased relative to locusts' preferred protein to carbohydrate ratio. This study highlights the importance of studying the nutritional ecology of animals in their environment and suggests that carbohydrate limitation may be a common pattern for migrating insect herbivores.
Plant carbohydrate content limits performance and lipid accumulation of an outbreaking herbivore
(Royal Society, 2020) Stav Talal; Arianne Cease; Jacob P. Youngblood; Ruth Farington; Eduardo V. Trumper; Héctor E. Medina; Julio Rojas; A. Fernando Copa; Jon F. Harrison
Locusts are major intermittent threats to food security and the ecological factors determining where and when these occur remain poorly understood. For many herbivores, obtaining adequate protein from plants is a key challenge. We tested how the dietary protein : non-structural carbohydrate ratio (p : c) affects the developmental and physiological performance of 4th-5th instar nymphs of the South American locust, Schistocerca cancellata, which has recently resurged in Argentina, Bolivia and Paraguay. Field marching locusts preferred to feed on high carbohydrate foods. Field-collected juveniles transferred to the laboratory selected artificial diets or local plants with low p : c. On single artificial diets, survival rate increased as foods became more carbohydrate-biased. On single local plants, growth only occurred on the plant with the lowest p : c. Most local plants had p : c ratios substantially higher than optimal, demonstrating that field marching locusts must search for adequate carbohydrate or their survival and growth will be carbohydrate-limited. Total body lipids increased as dietary p : c decreased on both artificial and plant diets, and the low lipid contents of field-collected nymphs suggest that obtaining adequate carbohydrate may pose a strong limitation on migration for S. cancellata . Anthropogenic influences such as conversions of forests to pastures, may increase carbohydrate availability and promote outbreaks and migration of some locusts.
Plant carbohydrate content limits performance and lipid accumulation of an outbreaking herbivore: Nutrition limits performance of locusts
(Royal Society, 2020) Stav Talal; Arianne Cease; Jacob P. Youngblood; Ruth Farington; Eduardo V. Trumper; Héctor E. Medina; Julio Rojas; A. Fernando Copa; Jon F. Harrison