Meeting Abstract
Migration is often associated with movement away from scarce nutrients or other resources, and yet migration itself is energetically demanding. Mormon crickets walk in dense aggregations over rangeland. In some of these migratory bands, Mormon crickets seek protein and salts, and they readily cannibalize wounded or dead band members. Hence, cannibalism leads to a forced march in collective motion. In other bands, Mormon crickets are deficient in carbohydrates, although they too will cannibalize when given the opportunity. Do these nutritional limitations result in trade-offs between migration and immunity? Feeding protein to protein-limited crickets slows the migration and increases generalized immunity, measured as phenoloxidase. In contrast, feeding carbohydrates to carb-limited crickets slows their migration and increases anti-bacterial activity. Do dietary deficiencies result in differences in susceptibility to pathogens? Protein-restricted diets caused Mormon crickets to have lower phenoloxidase titers, slower encapsulation of foreign bodies, and greater mortality from Beauveria bassiana fungal infection than they had when fed high protein diets. Hence diet altered fungal immunity. Anti-bacterial activity, in contrast, was dependent on combined effects of diet and migration. These two generalized immune functions are common to all insects and so the dichotomous role of nutritional deprivation can be generalized to all insect migrants. Climate may play an important role in the availability of protein and carbohydrates, and ultimately which of these two basic immune functions is weaker. Hence a changing climate may alter defenses of migrating insects and enhance or impede the spread of bacterial and fungal disease.
