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

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.

Climate warming can reduce biocontrol efficacy and promote plant invasion due to both genetic and transient metabolomic changes

“…The beetle Ophraella can strongly reduce the reproduction and population growth rate of Ambrosia in Europe (Augustinus, Lommen, et al, 2020; Augustinus, Sun, et al, 2020; Schaffner et al, 2020). However, based on our findings, we predict a reduced biocontrol efficacy under climate warming, highlighting the importance of accounting for the interplay between ecological and evolutionary processes in predicting biotic interactions in changing environments.…”

“…By adding or removing beetles, we maintained c. 50% visual leaf damage from August (after c. 2 beetle generations) to September (after c. 3 beetle generations). Damage levels are variable in the field, but often reach levels of 50% leaf damage by mid‐season (Augustinus, Lommen, et al, 2020). The Ophraella beetles used in all our experiments were from a mixture of five populations collected on repeated occasions within 30 km of the field experimental site.…”

The Changes of Soil Seed Banks In Time Series Before And After The Invasive Artemisia Trifida Was Removed From Grassland

“…Based on previous studies, it was found that the best control method for these invasive plants is to forbid produce seeds and consume the existing underground seed banks. For example, mowing or biological control of ragweed (Ambrosia artemisiifolia) in a specific period can reduce its seed yield and consume the seed bank (Basky et al 2017;Lommen et al 2018;Augustinus et al 2020). In farmland, the control can be achieved by formulating a rotation system between different crops to inhibit the germination of giant ragweed seeds and consume its seed bank (Goplen et al 2017).…”

Geographical dispersion of ragweed leaf beetle (Ophraella communa) based on climatic and biological characters in the Palearctic habitats

“…Based on the study of Zhou et al (2018), the female of O. communa uses primarily olfaction in quest of the host plants, but in the case of upwind directions, visual stimuli (e.g. leaf colour) can assist the insect in allocating its host plants, during which in the reproductive stage of the plant provides a biological sign for its herbivore in the form of the pollen dispersion (Augustinus, Lommen, et al, 2020). A. artemisiifolia growth is highly dependent on the soil disturbance level (Ziska et al, 2007), such as in Northern‐Italy, where is, in general, no soil cultivation after the harvest of cereals.…”

“…There are many local‐type studies from Europe and China which give population numbers of O. communa based on observations. Thus, detailed data were provided by Augustinus, Lommen, et al (2020) who predicted the impact of O. communa as a biocontrol agent based on the integrating distribution modelling with climate‐dependent vital rates. This study pointed out that egg hatching success strongly decreased from 80% to 20% when relative humidity drops from 55% to 45% during the day.…”