In-season leaf damage by a biocontrol agent explains reproductive output of an invasive plant species

Benno A Augustinus,Silvia Fogliatto,Maira Bonini,Tessa Smith,Francesco Vidotto,Heinz Müller-Schärer,Sandra Citterio,David Horvath,Suzanne T E Lommen,Rodolfo F Gentili,Urs Schaffner

doi:10.3897/neobiota.55.46874

Abstract

One of the biggest challenges in classical biological control of invasive weeds is predicting the likelihood of success. Ambrosia artemisiifolia, a North American plant species that has become invasive in Europe, causes economic losses due to health problems resulting from its huge amount of highly allergenic pollen and as a weed to agricultural crops resulting from high seed densities. Here we assessed whether the pollen and seed output of the annual A. artemisiifolia (at the end of the season) is related to in-season abundance of, or damage by, the accidentally introduced biological control agent Ophraella communa. We monitored the growth and leaf damage of individually labelled A. artemisiifolia plants at four locations in Northern Italy and recorded abundance of different O. communa life stages at regular intervals. We found that the in-season level of leaf damage by O. communa consistently helped to explain seed production in combination with plant volume and site throughout the season. Feeding damage, plant volume and site also explained pollen production by A. artemisiifolia six weeks before male flower formation. At three out of four sites, plants with more than 10% leaf damage in mid-June or early July had a very low likelihood of seed formation. Leaf damage proved to be a better explanatory variable than O. communa abundance. Our results suggest that the monitoring of the in-season leaf damage can help to project the local impact of O. communa on A. artemisiifolia at the end of the season and thus inform management regarding the needs for additional measures to control this prominent invader.

Highlights

It is well established that plant species that are introduced into areas outside their native range and become invasive can wreak serious impact on nature and human wellbeing (Vilà et al 2011)
A North American plant species that has become invasive in Europe, causes economic losses due to health problems resulting from its huge amount of highly allergenic pollen and as a weed to agricultural crops resulting from high seed densities
Our results suggest that the monitoring of the in-season leaf damage can help to project the local impact of O. communa on A. artemisiifolia at the end of the season and inform management regarding the needs for additional measures to control this prominent invader

Summary

Introduction

It is well established that plant species that are introduced into areas outside their native range and become invasive can wreak serious impact on nature and human wellbeing (Vilà et al 2011). One option to mitigate the negative impacts of invasive alien species is classical biological control, i.e. the use of specialist natural enemies from the native range to reduce invader densities below an economic and ecological threshold or to slow down their spread (Müller-Schärer and Schaffner 2008). Biological control agents need to reach high densities to impact the target plant to such an extent that vital rates, and its population growth rate, are negatively affected (Jamieson et al 2012). In cases of successful biological control of invasive alien plant species, population densities of the introduced biological control agents often reach numbers several orders higher than observed within their native range (Müller-Schärer and Schaffner 2008). Including biological control in integrated weed management presupposes an understanding of the likely abundance of the biological control agent and its impact on the target weed in a given region or year

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