Mixed infections and insect–pathogen interactions

Matthew B. Thomas*, Emma L. Watson and Pablo ValverdeGarcia Department of Agricultural Sciences, Imperial College, Wye, Kent TN25 5AH, UK Centre for Population Biology, Imperial College, Silwood Park, Ascot, Berks SL5 7PY, UK Entomologı́a Agrı́cola, Departamento de Ciencias y Recursos Agrı́colas y Forestales, ETSIAM, Universidad de Córdoba, Apartado 3048, Avda. Menéndez Pidal s ⁄n, 14080 Cordoba, Spain *Correspondence: E-mail: [email protected] Abstract Most studies of insect–pathogen interactions consider the direct interaction between one disease agent and one species of host. However, given that hosts are subject to challenge from many pathogen ⁄parasite species, mixed infections are probably common. In this study, using the desert locust and two species of fungal entomopathogen, we show how mixed infection with a largely avirulent pathogen can alter the virulence and reproduction of a second, highly virulent pathogen. We find that two strains of the avirulent pathogen vary in their interaction with the virulent pathogen, depending on the order of infection and environmental conditions. We propose that avirulent pathogens, which have largely been overlooked to date, could play a significant role in host– pathogen dynamics, with implications for biological control and evolution of virulence.