Linking Rangeland Management with the Nutritional Physiology and Ecology of Locusts

Rangeland management practices alter soil and plant characteristics and communities. These changes have implications for the success of pests common to grass and forage systems. Understanding how pests respond to anthropogenic influences is a key variable for the development of sustainable pest management strategies that minimize potential risk and severity of pest damage. For example, heavy livestock grazing in northeast China promotes locust outbreaks by lowering plant nitrogen content. This in turn likely decreases the amount of protein, relative to carbohydrate, that locusts receive. In this case, a low protein/high carbohydrate diet is just what this locust species needs to thrive. While many environmental factors influence locust outbreaks and plagues around the globe, understanding the interactions between livestock grazing, range quality, and locust populations is central to developing integrated control practices

Chapter 4 - Senegalese grasshopper—a major pest of the Sahel

International audienceLocust and grasshopper (family: Acrididae) outbreaks are ancient agricultural challenges and can be difficult to manage due to their fast population growth and high mobility. The Senegalese grasshopper (Oedaleus senegalensis Krauss, 1877) is a major Sahelian pest distributed from West Africa to India that attacks cereal crops. It typically has three generations during the rainy season, which sequentially migrate north to south with prevailing rains, and is highly responsive to land use and land cover change, preferring fallow fields. Depending on environmental conditions and the characteristics of the rainy season, outbreaks are observed throughout Sahelian countries from Senegal to Sudan. The National Plant Protection Organizations (NPPOs) of many Sahelian countries consider O. senegalensis a significant pest and include it in regular monitoring and treatment programs; however, resources are often limited. Community-based management in collaboration with NPPOs, as well as development of improved decision-making and management tools, can leverage existing infrastructures to advance sustainable pest management and food security

Nutritional imbalance suppresses migratory phenotypes of the Mongolian locust (Oedaleus asiaticus)

For many species, migration evolves to allow organisms to access better resources. However, the proximate factors that trigger these developmental changes, and how and why these vary across species, remain poorly understood. One prominent hypothesis is that poor-quality food promotes development of migratory phenotypes and this has been clearly shown for some polyphenic insects. In other animals, particularly long-distance bird migrants, it is clear that high-quality food is required to prepare animals for a successful migration. We tested the effect of diet quality on the flight behaviour and morphology of the Mongolian locust, Oedaleus asiaticus. Locusts reared at high population density and fed low-N grass (performance-enhancing for this species) had enhanced migratory morphology relative to locusts fed high-N grass. Furthermore, locusts fed synthetic diets with an optimal 1 : 2 protein : carbohydrate ratio flew for longer times than locusts fed diets with lower or higher protein : carbohydrate ratios. In contrast to the hypothesis that performance-degrading food should enhance migration, our results support the more nuanced hypothesis that high-quality diets promote development of migratory characteristics when migration is physiologically challenging

Data from: Nutritional imbalance suppresses migratory phenotypes of the Mongolian locust (Oedaleus asiaticus)

For many species, migration evolves to allow organisms to access better resources. However, the proximate factors that trigger these developmental changes, and how and why these vary across species, remain poorly understood. One prominent hypothesis is that poor-quality food promotes development of migratory phenotypes and this has been clearly shown for some polyphenic insects. In other animals, particularly long-distance bird migrants, it is clear that high-quality food is required to prepare animals for a successful migration. We tested the effect of diet quality on the flight behaviour and morphology of the Mongolian locust, Oedaleus asiaticus. Locusts reared at high population density and fed low-N grass (performance-enhancing for this species) had enhanced migratory morphology relative to locusts fed high-N grass. Furthermore, locusts fed synthetic diets with an optimal 1 : 2 protein : carbohydrate ratio flew for longer times than locusts fed diets with lower or higher protein : carbohydrate ratios. In contrast to the hypothesis that performance-degrading food should enhance migration, our results support the more nuanced hypothesis that high-quality diets promote development of migratory characteristics when migration is physiologically challenging

Grasshoppers Regulate N:P Stoichiometric Homeostasis by Changing Phosphorus Contents in Their Frass

<div><p>Nitrogen (N) and phosphorus (P) are important limiting nutrients for plant production and consumer performance in a variety of ecosystems. As a result, the N:P stoichiometry of herbivores has received increased attention in ecology. However, the mechanisms by which herbivores maintain N:P stoichiometric homeostasis are poorly understood. Here, using a field manipulation experiment we show that the grasshopper <i>Oedaleus asiaticus</i> maintains strong N:P stoichiometric homeostasis regardless of whether grasshoppers were reared at low or high density. Grasshoppers maintained homeostasis by increasing P excretion when eating plants with higher P contents. However, while grasshoppers also maintained constant body N contents, we found no changes in N excretion in response to changing plant N content over the range measured. These results suggest that <i>O. asiaticus</i> maintains P homeostasis primarily by changing P absorption and excretion rates, but that other mechanisms may be more important for regulating N homeostasis. Our findings improve our understanding of consumer-driven P recycling and may help in understanding the factors affecting plant-herbivore interactions and ecosystem processes in grasslands.</p></div

Correlations between N and P concentrations in grasshopper body (a), frass (b), and food plants (c) of grasshopper <i>Oedaleus asiaticus.</i>

<p>Correlations between N and P concentrations in grasshopper body (a), frass (b), and food plants (c) of grasshopper <i>Oedaleus asiaticus.</i></p

Responses of N and P contents and N:P stoichiometry, of food plants (a–c), grasshopper body (d–f) and frass (g–i), to increasing grasshopper density.

<p>Error bars indicate ±1 SE. In (a), a strong negative relationship was found between host plant N concentrations and grasshopper density (ANOVA: <i>r²</i> = 0.93, <i>F</i> = 51.16, <i>P</i> = 0.002) and yielded the following equation: y = −0.13 x+14.52. In (b), a strong negative relationship was found between host plant N concentrations and grasshopper density (ANOVA: <i>r²</i> = 0.86, <i>F</i> = 23.59, <i>P</i> = 0.008) and yielded the following equation: y = −0.01 x+1.17. In (h), a marginally negative relationship was found between frass P concentrations and grasshopper density (ANOVA: <i>r²</i> = 0.65, <i>F</i> = 5.69, <i>P</i> = 0.097) and yielded the following equation: y = −0.025 x+2.14.</p

Results (<i>F</i> and <i>P</i> values) of one-way ANOVAs on the effects of grasshopper density on N:P ratio of food plant, grasshopper body and frass, corresponding to Figure 2.

<p>Results (<i>F</i> and <i>P</i> values) of one-way ANOVAs on the effects of grasshopper density on N:P ratio of food plant, grasshopper body and frass, corresponding to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0103697#pone-0103697-g002" target="_blank">Figure 2</a>.</p

The effects of food plant N:P stoichiometry on N concentrations, P concentrations, N:P ratios in grasshopper body and frass.

<p>Error bars indicate ±1 SE. In (e), a strong positive relationship was found between frass and food plant P concentrations (ANOVA: <i>r²</i> = 0.85, <i>F</i> = 17.65, <i>P</i> = 0.025) and yielded the following equation: y = 3.13 x−1.43.</p