Water Restrictions and Macronutrient Level Intake of Locust

Locust are grasshoppers that tend to migrate in swarms that can cause major damage to agriculture. Chortoicetes terminifera are locust native to Australian deserts, where they can potentially experience water restrictions. I hypothesized that water restriction would slow growth; and that high‐protein diets will be more deleterious under water‐restricted conditions because nitrogenous wastes require water to eliminate. Locusts were collected on the day they molted into the fifth (final) instar, weighed and placed in an individual plastic cage. Locusts received ad lib quantities of two different dry, granular diets: 35% protein:7% carbohydrate or 14% protein:28% carbohydrate. Locusts either had unlimited water or had ad lib access to water during every third day. All locust were given water on the day they molted for 24 hours. Then the locust on the restricted water treatment had no water for two days, followed by 24 hours with water, then 48 hours without water, continuing this pattern until the locust molted. After the locusts molted into adults, which took approximately 10 – 15 days, their final body mass (wet and dry) was recorded. Consumption rate was calculated by the loss in mass of the food pile over the entire instar, and their growth rates from the change in wet mass and development time (measured with a precision of ±1 day). Water restriction did not affect body water content or many measures of growth and size, suggesting this was a mild stress. Sexes differed in their responses, with water restriction reducing growth in males but not females. However, size and growth of females were much more affected by the diet than males; with the high‐protein diet strongly lowering body mass, food consumption and growth rate in females. Males consumed less of the high‐protein diet, but their adult mass and growth rate were unaffected by diet. High protein diets increased body water content for both sexes, possibly because high carbohydrate diets were associated with an increase in fat storage. There were few interactions between diet and water restriction, and contrary to our hypothesis, no consistent evidence that high‐protein diets were more deleterious under water restricted conditions. Future studies should examine the sex‐specific growth and metabolic responses to dietary protein:carbohydrate content. This research project was made possible thanks supported by the American Physiological Society and a grant from the National Science Foundation Integrative Organismal Systems IOS‐1238831 as well as the DEB 1313696, and CHE 1313958. Support or Funding Information This research project was made possible thanks supported by the American Physiological Society and a grant from the National Science Foundation Integrative Organismal Systems IOS‐1238831 as well as the DEB 1313696 and CHE 1313958.