Population dynamic consequences of parasitised-larval competition in stage-structured host?parasitoid systems

Abstract

Parasitism can influence many aspects of the host's behaviour and physiology, which in turn can have a profound impact on their population and evolutionary ecology. In many host Áparasite interactions there is often a time lag between infection and the death of the host, yet little is known, experimentally or theoretically, about the effects that intra-class competition between parasitised and unparasitised hosts have on the host Á parasite population dynamics.In this article we address this gap in our understanding using a stage-structured mathematical model for a host Áparasitoid interaction, which has been parameterised for the Plodia ÁVenturia experimental system.In the case where parasitised larvae do not compete and do not cannibalise unparasitised larvae, our model predicts a wide range of host Áparasitoid dynamics, ranging from host Áparasitoid generation cycles, to host generation cycles with parasitoid half-generation cycles, to host Áparasitoid equilibria, to host generation cycles with parasitoid extinction.However, when parasitised larvae can compete with their unparasitised larvae counterparts, the host Á parasitoid population dynamics can dramatically change. In particular, we show that high levels of competition exerted by unparasitised larvae upon parasitised larvae is more likely to lead to parasitoid extinction.In addition, we demonstrate that unparasitised host larvae that are sufficiently susceptible to intra-class competition, or parasitised host larvae that are sufficiently strong competitors, can have a stabilising effect on the host Áparasitoid population dynamics.The implications of these theoretical results are discussed in light of our understanding of host Áparasitoid interactions and host Áparasite systems in general.

Resource competition and shared natural enemies in experimental insect communities

“…If host populations are experiencing high levels of resource competition aVecting both individual survival and quality then the parasitoid too will suVer and its population growth rate may fall below zero so that it is unable to invade. This eVect will be exacerbated if parasitised hosts are particularly susceptible to density-dependent mortality, as has been observed in some aphid parasitoid systems (Ives and Settle 1995), though examples exist of interactions where parasitised hosts are at a competitive advantage (Spataro and Bernstein 2004;Cameron et al 2007;White et al 2007). By the time we released parasitoids into our microcosms, aphid densities were already high and intraspeciWc competition severe, and this may have hindered their ability to invade and persist.…”

Modelling pulsed releases for sterile insect techniques: fitness costs of sterile and transgenic males and the effects on mosquito dynamics

“…However, these models fail to take into account the stage‐structured life‐history of the insects, which can have significant effects on their dynamics, [but see Barclay (1980) and Esteva & Mo Yang (2005) for example] as found in many other models of insect population dynamics (Wearing et al. 2004; White, Sait & Rohani 2007), where short‐period population oscillations in abundance occur from the developmental lags between life‐history stages (Murdoch, Briggs & Nisbet 2003). In the case of late‐acting bisex RIDL, since the late‐acting system kills the heterozygous offspring after the density‐dependent larval stage, additional mortality occurs in the wild‐type population.…”

Effects of phenological mismatch under warming are modified by community context

“…This can reduce population growth to rates that cannot support long‐term parasitoid persistence (Cuny et al, 2019; Jones et al, 2009). Furthermore, if parasitized hosts are more inclined to density‐dependent mortality, as observed in some (Ives & Settle, 1996), but not in all host‐parasitoid systems (Spataro & Bernstein, 2004; White et al, 2007), this effect is likely to be amplified. Overall, these results suggest that extending the temporal availability of hosts via competition is unlikely to dampen the impact of phenological shifts.…”