Fungal disease dynamics in insect societies: Optimal killing rates and the ambivalent effect of high social interaction rates Journal Article

Author(s): Novak, Sebastian; Cremer, Sylvia
Article Title: Fungal disease dynamics in insect societies: Optimal killing rates and the ambivalent effect of high social interaction rates
Affiliation IST Austria
Abstract: Entomopathogenic fungi are potent biocontrol agents that are widely used against insect pests, many of which are social insects. Nevertheless, theoretical investigations of their particular life history are scarce. We develop a model that takes into account the main distinguishing features between traditionally studied diseases and obligate killing pathogens, like the (biocontrol-relevant) insect-pathogenic fungi Metarhizium and Beauveria. First, obligate killing entomopathogenic fungi produce new infectious particles (conidiospores) only after host death and not yet on the living host. Second, the killing rates of entomopathogenic fungi depend strongly on the initial exposure dosage, thus we explicitly consider the pathogen load of individual hosts. Further, we make the model applicable not only to solitary host species, but also to group living species by incorporating social interactions between hosts, like the collective disease defences of insect societies. Our results identify the optimal killing rate for the pathogen that minimises its invasion threshold. Furthermore, we find that the rate of contact between hosts has an ambivalent effect: dense interaction networks between individuals are considered to facilitate disease outbreaks because of increased pathogen transmission. In social insects, this is compensated by their collective disease defences, i.e., social immunity. For the type of pathogens considered here, we show that even without social immunity, high contact rates between live individuals dilute the pathogen in the host colony and hence can reduce individual pathogen loads below disease-causing levels.
Keywords: social immunity; epidemiological model; basic reproduction number; obligate killing entomopathogenic fungi; biological control
Journal Title: Journal of Theoretical Biology
Volume: 372
ISSN: 0022-5193
Publisher: Elsevier  
Date Published: 2015-05-07
Start Page: 54
End Page: 64
Sponsor: This work has been funded by the European Research Council (ERC Advanced Grant no. 250152 to N.H. Barton and ERC Starting Grant no. 243071 to S. Cremer)
DOI: 10.1016/j.jtbi.2015.02.018
Notes: We thank Nick Barton for discussion and advice throughout the progress of this work and Line V. Ugelvig, Barbara Casillas-Perez, Rodrigo Redondo, and Carsten Marr, as well as an anonymous reviewer and the editor for their constructive comments that greatly improved the manuscript.
Open access: yes (repository)