title: Effects of phenotypic plasticity on pathogen transmission in the field in a Lepidoptera-NPV system.
abstract: In models of insect-pathogen interactions, the transmission parameter (ν) is the term that describes the efficiency with which pathogens are transmitted between hosts. There are two components to the transmission parameter, namely the rate at which the host encounters pathogens (contact rate) and the rate at which contact between host and pathogen results in infection (host susceptibility). Here it is shown that in larvae of Spodoptera exempta (Lepidoptera: Noctuidae), in which rearing density triggers the expression of one of two alternative phenotypes, the high-density morph is associated with an increase in larval activity. This response is likely to result in an increase in the contact rate between hosts and pathogens. Rearing density is also known to affect susceptibility of S. exempta to pathogens, with the high-density morph showing increased resistance to a baculovirus. In order to determine whether density-dependent differences observed in the laboratory might affect transmission in the wild, a field trial was carried out to estimate the transmission parameter for S. exempta and its nuclear polyhedrosis virus (NPV). The transmission parameter was found to be significantly higher among larvae reared in isolation than among those reared in crowds. Models of insect-pathogen interactions, in which the transmission parameter is assumed to be constant, will therefore not fully describe the S. exempta-NPV system. The finding that crowding can influence transmission in this way has major implications for both the long-term population dynamics and the invasion dynamics of insect-pathogen systems.
authors.affiliation: NERC Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford, OX1 3SR, UK e-mail: rha@ceh.ac.uk, Fax: +44-1865-281696, , , , , , GB.
authors.forename: A F
authors.initials: AF
authors.lastname: Reeson
authors.affiliation: Institute of Biological Sciences, University of Stirling, Stirling, FK9 4LA, UK, , , , , , GB.
authors.forename: K
authors.initials: K
authors.lastname: Wilson
authors.affiliation: NERC Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford, OX1 3SR, UK e-mail: rha@ceh.ac.uk, Fax: +44-1865-281696, , , , , , GB.
authors.forename: J S
authors.initials: JS
authors.lastname: Cory
authors.affiliation: NERC Institute of Terrestrial Ecology, Monks Wood, Huntingdon, Cambridgeshire, PE17 2LS, UK, , , , , , GB.
authors.forename: P
authors.initials: P
authors.lastname: Hankard
authors.affiliation: NERC Institute of Terrestrial Ecology, Monks Wood, Huntingdon, Cambridgeshire, PE17 2LS, UK, , , , , , GB.
authors.forename: J M
authors.initials: JM
authors.lastname: Weeks
authors.affiliation: Biodiversity and Ecology Division, School of Biological Sciences, University of Southampton, Southampton, SO16 7PX, UK, , , , , , GB.
authors.forename: D
authors.initials: D
authors.lastname: Goulson
authors.affiliation: NERC Institute of Virology and Environmental Microbiology, Mansfield Road, Oxford, OX1 3SR, UK e-mail: rha@ceh.ac.uk, Fax: +44-1865-281696, , , , , , GB.
authors.forename: R S
authors.initials: RS
authors.lastname: Hails
keywords: Baculoviruses; Key words Transmission; Mass action assumption; Phase polyphenism; Spodoptera exempta