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

Abstract

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.

A Global Review on Locusts (Orthoptera: Acrididae) and Their Interactions With Livestock Grazing Practices

“…There are multiple factors that might explain why carbohydrate-biased diets are beneficial for locusts. First, carbohydrate-biased diets may be a requirement for longdistance flight (Hunter et al, 1981;Cease et al, 2017). A defining characteristic of locusts is their capacity to undergo spectacular migrations: swarms can fly hundreds of kilometers in a single night and plagues can span continents.…”

“…This pattern matches with the species of host plants preferred by O. asiaticus. Counterintuitively, even though Stipa spp tend to have lower nitrogen and protein contents than Leymus and other common grasses, it is generally preferred by O. asiaticus (Liu et al, 2013a;Cease et al, 2017;Huang et al, 2017b). This is likely due to its low protein and high carbohydrate content; although secondary metabolites may also play a role (Li et al, 2019).…”

“…This is likely due to its low protein and high carbohydrate content; although secondary metabolites may also play a role (Li et al, 2019). These carbohydrate-biased diets increase growth rate, survival, and migratory capacity for O. asiaticus (Cease et al, 2012(Cease et al, , 2017.…”

Social nutrition: an emerging field in insect science

“…Cannibalistic interactions result in a push-pull mechanism in which insects move to reduce their risk of being eaten, while chasing ahead for potential victims, leading to the formation of marching bands at critical population densities [29,30]. Larger scale migrations of flying adults, however, have been associated with a nutritional balance [31]. In the Mongolian locust (Oedaleus asiaticus), adults artificially fed balanced (low-protein) diets have increased muscle size and fuel stores, and thus fly for longer than individuals fed imbalanced (very low-or high-protein) diets [31].…”

“…Larger scale migrations of flying adults, however, have been associated with a nutritional balance [31]. In the Mongolian locust (Oedaleus asiaticus), adults artificially fed balanced (low-protein) diets have increased muscle size and fuel stores, and thus fly for longer than individuals fed imbalanced (very low-or high-protein) diets [31]. In the Eurasian steppe, heavy livestock grazing and grassland degradation (loss of organic N) promotes locust outbreaks by shifting plant nutrient content toward optimal lowprotein diets favourable to migratory morphs [32].…”