Changes in parasitoid communities over time and space: a historical case study of the maize pest Ostrinia nubilalis.

Laurent Folcher,Denis Bourguet,Nathalie Eychenne,Michel Phalip,Laurent Pélozuelo,Alain Weissenberger,Catherine Regnault-Roger,Marc Delos,Denis Thiéry

doi:10.1371/journal.pone.0025374

Abstract

Understanding the ways in which human environmental modifications affect biodiversity is a key challenge in conservation planning, pest control and evolutionary ecology. Parasitoid communities, particularly those associated with agricultural pests, may be susceptible to such modifications. We document here changes in the larval parasitoid communities of Ostrinia nubilalis — the main pest of maize — and its sibling species O. scapulalis, based on two historical datasets, one collected from 1921–1928 and the other from 2001–2005. Each of these datasets encompasses several years and large geographical areas and was based on several thousands/millions of host larvae. The 80-year interval between the two datasets was marked by a decrease in O. nubilalis parasitism to about two thirds its initial level, mostly due to a decrease in the rate of parasitism by hymenopterans. However, a well balanced loss and gain of species ensured that species richness remained stable. Conversely, O. scapulalis displayed stable rates of parasitism over this period, with a decline in the species richness of its parasitoid community. Rates of parasitism and species richness in regions colonized by O. nubilalis during the 1950s were one half to one third those in regions displaying long-term colonisation by this pest. During the recent human activity-driven expansion of its range, O. nubilalis has neither captured native parasitoids nor triggered parasite spill back or spill over.

Highlights

Human activity exerts strong selective pressures on all kind of species and on communities of species [1,2,3,4,5,6]
Pesticide and fertiliser applications, the conversion of natural ecosystem to agricultural fields, modifications to ecosystems or landscapes by urbanization and any other change triggered by human activity induced significant changes within parasitoid communities, among parasitoids infesting agricultural pests [34,35,8]
We document here the changes that have occurred in parasitoid communities for the European corn borer (ECB), the main pest of maize, based on two substantial historical datasets

Summary

Introduction

Human activity exerts strong selective pressures on all kind of species and on communities of species [1,2,3,4,5,6]. These selective pressures arise from diverse sources, including global warming, the use of pesticides and drugs in agriculture and medicine, land transformation (land clearing, fire suppression, cultivation, deforestation, urbanization etc.) and pollutants from industry and various types of traffic. Landscape fragmentation can increase the heterogeneity of the environment, resulting in a diversity of habitats favouring a high species richness [10,11]. In most cases, habitat fragmentation and environmental degradation lead to a decrease in species richness in most communities of species [13,14,15,16]

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Conclusion