ORIGINAL PAPER Comparison of the energetic stress associated with experimental Nosema ceranae and Nosema apis infection of honeybees (Apis mellifera) Raquel Martín-Hernández & Cristina Botías & Laura Barrios & Amparo Martínez-Salvador & Aránzazu Meana & Christopher Mayack & Mariano Higes Received: 20 November 2010 / Accepted: 9 February 2011 / Published online: 1 March 2011 # Springer-Verlag 2011 Abstract Nosema ceranae is a relatively new and wide- spread parasite of the western honeybee Apis mellifera that provokes a new form of nosemosis. In comparison to Nosema apis, which has been infecting the honeybee for much longer, N. ceranae seems to have co-evolved less with this host, causing a more virulent disease. Given that N. apis and N. ceranae are obligate intracellular micro- sporidian parasites, needing host energy to reproduce, energetic stress may be an important factor contributing to the increased virulence observed. Through feeding experi- ments on caged bees, we show that both mortality and sugar syrup consumption were higher in N. ceranae- infected bees than in N. apis-infected and control bees. The mortality and sugar syrup consumption are also higher in N. apis-infected bees than in controls, but are less than in N. ceranae-infected bees. With both microsporidia, mortal- ity and sugar syrup consumption increased in function of the increasing spore counts administered for infection. The differences in energetic requirements between both Nosema spp. confirm that their metabolic patterns are not the same, which may depend critically on host–parasite interactions and, ultimately, on host pathology. The repercussions of this increased energetic stress may even explain the changes in host behavior due to starvation, lack of thermoregulatory capacity, or higher rates of trophallaxis, which might enhance transmission and bee death. Introduction It is obvious that, when a parasite outcompetes its host for the nutrient resources available, the host itself will suffer severe energetic stress. Infected hosts may appear to compensate for such a situation by feeding more, although they also are less efficient in obtaining energy than uninfected hosts. Therefore, not only do parasites take nutrients and energy away from hosts, but they also lower the rate at which energy becomes available for hosts to carry out vital functions (Walkey and Meakins 1970). Changes in feeding behavior following infection are just one example of the many potential alterations that might arise due to the need to assimilate more nutrients (Milinski 1985), and indeed, energetic stress typically underlies many of the physiological and behavioral alterations induced by infection (Milinski 1984). Microsporidia are spore-forming fungal pathogens that develop as obligate intracellular organisms and infect a wide variety of hosts, ranging from insects to mammals (Adl et al. 2005). As they lack mitochondria and reproduce rapidly within a host cell, taking up ATP from their surroundings, parasitic microsporidia are particularly likely to exert severe R. Martín-Hernández : C. Botías : M. Higes (*) Bee Pathology Laboratory, Centro Apícola Regional, JCCM, San Martín s/n, 19180 Marchamalo, Guadalajara, Spain e-mail: mhiges@jccm.es L. Barrios Statistics Department, CTI, Consejo Superior Investigaciones Científicas, 28006 Madrid, Spain A. Martínez-Salvador Epidemiology Department, TRAGSEGA, Madrid, Spain A. Meana Animal Health Department, Facultad de Veterinaria, Universidad Complutense de Madrid, 28040 Madrid, Spain C. Mayack Department of Biology, Colorado State University, Fort Collins, CO 80523, USA Parasitol Res (2011) 109:605–612 DOI 10.1007/s00436-011-2292-9