Like marathon runners, locusts carbo-load before a long journey

A study published Aug. 2 in the Journal of Animal Ecology finds that migrating locusts carbo-load before flying up to 350 kilometers in a single night.

Marion Le Gall, an assistant research professor in the Global Locust Initiative in the Global Institute of Sustainability and Innovation, conducted a locust field study in 2017 in Senegal.

Her findings showed that Mongolian locusts did better in overgrazed pastures than in a normal pasture. Co-author and sustainability scientist Arianne Cease tied this to the nutritional content of plants: Land that was overgrazed contained less nitrogen and plants were more sugar-based. That was good for the locusts.

The abstract follows.

  1. Nitrogen limitation theory predicts that terrestrial plants should benefit from nitrogen inputs and that herbivores should benefit from subsequent higher plant protein contents. While this pattern has generally been supported, some herbivorous insects have shown preference and higher performance on low protein (p), high carbohydrate (c) diets as juveniles.
  2. However, little is known about the effects on reproduction in adults. Using nitrogen fertilizer, we demonstrate that high plant p:c has negative effects on Senegalese locust (Orthoptera: Oedaeleus senegalensis) reproduction and survival in an agroecological setting.
  3. For this, we measured p:c in millet plants Pennisetum glaucum that received two levels of fertilizer (high and moderate) and a control, then we caged locusts on these plants for 2 weeks. In the laboratory, we gave locusts the choice between untreated millet leaves and leaves that received one of the two fertilization treatment.
  4. We found that fertilization increased p:c ratio in a concentration‚Äźdependent fashion. We counted the number of locusts alive over the course of 2 weeks and showed that fewer females survived on fertilized plants than on control plants. Females that ate plants from the high fertilization treatment laid lighter eggs. Finally, we showed that female locusts prefer unfertilized plants to plants with a high p:c.
  5. We hypothesize that this pattern will apply broadly to species that have extensive carbohydrate needs, such as long‚Äźdistance migrators. Because many ecological studies focus primarily on nitrogen or protein, and fail to consider carbohydrates, this study has important implications for how ecologists consider nutrient limitation of primary consumers in ecosystems globally.