Costs and Benefits of Behavioral Fever in Melanoplus sanguinipes Infected by Nosema acridophagus

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Abstract
Per os inoculations of migratory grasshoppers Melanoplus sanguinipes with the microsporidian protozoan Nosema acridophagus resulted in an increase in the grasshoppers' preferred temperature by about 6 C. Maintenance of grasshoppers at febrile and nonfebrile temperatures showed that fever benefited infected grasshoppers in terms of survival and growth. Febrile temperatures negatively affected the growth of uninfected grasshoppers, but, for infected grasshoppers, these costs were outweighed by the benefits. Nonfebrile infected M. sanguinipes were less fecund than nonfebrile controls, while fecundity of febrile infected M. sanguinipes did not differ significantly from febrile controls. This investigation is, to our knowledge, the first to show that (1) protozoal infections can generate fever in an ectotherm, (2) the costs of fever involve decreased growth rate of the host, and (3) a net benefit of fever occurs when the pathogen is introduced to the host by a natural route.