Host Suppression and Stability in a Parasitoid-Host System: Experimental Demonstration

Abstract

We elucidate the mechanisms causing stability and severe resource suppression in a consumer-resource system. The consumer, the parasitoid Aphytis, rapidly controlled an experimentally induced outbreak of the resource, California red scale, an agricultural pest, and imposed a low, stable pest equilibrium. The results are well predicted by a mechanistic, independently parameterized model. The key mechanisms are widespread in nature: an invulnerable adult stage in the resource population and rapid consumer development. Stability in this biologically nondiverse agricultural system is a property of the local interaction between these two species, not of spatial processes or of the larger ecological community.

Diferentes escalas de reprodução e migração em um sistema presa-predador com estrutura espacial

“…Na natureza encontramos muitos exemplos de interações nas quais uma espécie reproduz-se em intervalos de tempo menores do que a outra: podemos citar joaninhas predando afídeos [2], doninhas atacando pequenos roedores [6], controle da cochonilha vermelha (Aonidiella auranti) pelo parasitóide Aphytis melinus [4].…”

Theoretical contributions to biological control success

“…Stability was not confirmed by modeling. However, the stability of this system has been repeatedly demonstrated empirically by pulse perturbation experiments, a generally accepted method of demonstrating population regulation (Murdoch et al 2005;Murdoch 1970). Create an upsurge in ragwort abundance and natural enemies readily colonize and return the population to pre-perturbation levels in ragwort populations exposed to natural enemies in open cages.…”

“…The model reproduced the dynamics of the perturbed populations with remarkable accuracy, and the model result was robust to substantial changes in parameter values and even to structural changes in the model. To generalize these results, it was possible to survey other parasitoid-host systems for control of scale insects to discover whether similar ecological attributes are shared across taxonomically-related biological control systems (Murdoch et al 2005). Few other cases have been studied in sufficient detail, but 16 cases of biological control of coccids appear to share four main features: (1) the interaction is persistent, and perhaps stable, (2) control is attributed (at least locally) to a single parasitoid, (3) the pest has an invulnerable stage, and (4) the enemy development time is shorter than that of the pest.…”

“…The takeaway lessons from this decades-long study are (1) the mechanisms regulating biological control systems cannot simply be deduced from mathematical models, they must also be confirmed by rigorous empiricism including field observations and manipulative experiments, (2) this parasitoid-host interaction is highly stable and is regulated at the level of the individual citrus tree, (3) stabilizing mechanisms are linked to stage structure (developmental responses and invulnerable stages), (4) the stage-structured model developed for this system faithfully describes the return to equilibrium following a pulse, experimental perturbation (Murdoch et al 2005). It is an open question whether conclusions from this study can be generalized beyond parasitoids interacting with scale hosts, mainly because too few systems have been studied in sufficient detail.…”

“…Feasible remaining mechanisms for stability were explored using a pulse, density-perturbation experiment that might uncover both density-dependence and the regulating mechanisms causing return to equilibrium. The experiment was coupled with a detailed day-to-day stage-structured model of the system of interactions incorporating candidate regulatory mechanisms, with parameters estimated independent of the experiment (Murdoch et al 2005). The model distinguished scale stages and their differential use by Aphytis, and it addressed three remaining mechanisms by which the system might be stabilized: (1) there is a long-lived invulnerable adult scale stage, (2) the wasp Aphytis develops (about three times) faster than the scale, (3) an attack on older immature scale yields more parasitoid offspring than an attack on younger immature scale (the developmental 'gain mechanism')-for example, attack on older scale yields one or more female parasitoid offspring directly, while host-feeding on the youngest scale yields fewer offspring indirectly by providing the adult female with nutrients for egg development.…”