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.
Locusts have been reported to elevate metabolic rate in response to high carbohydrate diets; this conclusion was based on metabolic rates calculated from CO2 production, a common practice for insects. However, respiratory exchange ratios (RER, CO2 production divided by O2 consumption) can rise above 1 due to de novo lipid synthesis, providing an alternate possible explanation of the prior findings. We studied the relationship between macronutrient ingestion, RER, and lipid synthesis using South American locusts (Schistocerca cancellata) reared on artificial diets varying in protein:carbohydrate (p:c) ratio. RER increased and rose above 1 as dietary p:c decreased. Lipid accumulation rates were strongly positively correlated with dietary carbohydrate content and ingestion. RERs above 1 were only observed for animals without food in the respirometry chamber, suggesting that hormonal changes after a meal may drive lipid synthesis. S. cancellata does not elevate metabolic rate on low p:c diets; in fact, the opposite trend was observed.
El karst del estado de Yucatán, México, tiene su origen en los arrecifes coralinos y sedimentos marinos que, al exponerse a la superficie, formaron la roca caliza. Los procesos de solubilización-precipitación de esta roca han promovido la ausencia de corrientes de agua superficiales, un relieve ligeramente ondulado con planicies, depresiones y montículos, afloramientos y presencia de cenotes. Los diferentes grados de porosidad y dureza de la roca han permitido la formación desde pequeñas oquedades y acumulaciones de suelo, hasta complejos sistemas de cuevas secas y húmedas. El manejo de este tipo de áreas debe partir del conocimiento de su origen, morfología y biología para garantizar el uso sustentable de los recursos naturales. Se requiere especial atención en el manejo de la extracción de roca caliza, las actividades turísticas y productivas relacionadas con el uso de agua del acuífero, así como el volumen y calidad de las descargas de aguas residuales al suelo, cenotes y el mar.
An assessment of the extinction risk of the endemic plants from the Yucatán Peninsula Biotic Province (YPBP) was performed based on distributional data (B criteria of the IUCN) using the GeoCAT tool. The YPBP is located in southeastern Mexico and comprises the Mexican states of Campeche, Quintana Roo, and Yucatán, and the northernmost portion of Belize (districts of Belize, Corozal, and Orange Walk), as well as a portion of northern Guatemala (most of the department of Petén). An analysis of the YPBP flora identified 167 endemic taxa, 154 of which grow in at least one of the three Mexican states (Campeche, Quintana Roo, and/or Yucatán), whereas another 13 occur exclusively in Belize and/or Guatemala. Eighty-five are in some category of risk (50.9%): 17 taxa (10.18%) are categorized as Critically Endangered (CR), 40 (23.95%) as Endangered (EN), and 28 (16.77%) as Vulnerable (VU). Eighty-one (48.5%) species are not threatened: 12 (7.19%) as Near Threatened (NT) and 69 (41.32%) as Least Concern. A single species (0.6%) is considered Data Deficient (DD). The greatest number of endemic species and endemic threatened species inhabit dry and subhumid forests, and some inhabit semi-evergreen forests. The habits of endemic species and threatened endemic species are diverse, but trees, grasses, and shrubs predominate. The official system of protected natural areas (PNA) does not guarantee the conservation of all endemic species in the region. Ninety-eight (58.68%) of the endemic taxa have more than one population (record) within a PNA.
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