Predicting impact of a biocontrol agent: integrating distribution modeling with climate‐dependent vital rates

Abstract

Species distribution models can predict the suitable climatic range of a potential biological control agent (BCA), but they provide little information on the BCA's potential impact. To predict high population buildup, a prerequisite of biocontrol impact, studies are needed that assess the effect of environmental factors on vital rates of a BCA across the environmental gradient of the BCA's suitable habitats, especially for the region where the BCA is considered for field release. We extended a published species distribution model with climate‐dependent vital rates of Ophraella communa, a recently and accidentally introduced potential BCA of common ragweed, Ambrosia artemisiifolia in Europe. In field and laboratory experiments, we collected data on climate‐dependent parameters assumed to be the most relevant for the population buildup of O. communa, i.e., temperature driving the number of generations per year and relative humidity (RH) determining egg hatching success. We found that O. communa concluded one generation in 334 cumulative degree days, and that egg hatching success strongly decreased from > 80% to < 20% when RH drops from 55% to 45% during the day. We used these values to spatially explicitly project population densities across the European range suitable for both A. artemisiifolia and the beetle and found that the present distribution of the beetle in Europe is within the range with the highest projected population growth. The highest population density of O. communa was predicted for northern Italy and parts of western Russia and western Georgia. Field observations of high impact on A. artemisiifolia with records of 80% aerial pollen reduction in the Milano area since the establishment of O. communa are in line with these predictions. The relative importance of temperature and RH on the population density of O. communa varies considerably across its suitable range in Europe. We propose that the combined statistical and mechanistic approach outlined in this paper helps to more accurately predict the potential impact of a weed BCA than a species distribution model alone. Identifying the factors limiting the population buildup of a BCA across the suitable range allows implementation of more targeted release and management strategies to optimize biocontrol efficacy.

Biocontrol of invasive weeds under climate change: progress, challenges and management implications

“…Moreover, combining SDM and mechanistic (process-based) models by integrating physiological models of insect development into SDMs based on habitat suitability may enable more robust predictions of both range shifts [41] and population abundances [42,43]. Using such a combined approach, Augustinus et al [44] identified the climatic factors limiting the population build-up of Ophraella communa Lesage (Coleoptera: Chrysomelidae), a biocontrol candidate of invasive A. artemisiifolia, and predicted its potential population density across its suitable European range and the relative importance of those climatic factors on population growth. Population dynamics models are also commonly used to explore and predict changes in population densities over time, such as Integral Projection Models (IPMs) [45] and DYMEX (Hearne Scientific Software) [46].…”

Is biocontrol efficacy rather driven by the plant or the antagonist genotypes? A conceptual bioassay approach

“…Moreover, seven traits were only significantly affected by Ophraella genotype including L1 and L3 survival, adult emergence, developmental time and relative water content of adults. Previous studies on Ophraella showed that a higher survival and faster developmental time would result in a higher population increase and more efficient control of Ambrosia (Augustinus et al 2020). Furthermore, larger body size in insects is generally linked to greater fecundity and access to mates (Blanckenhorn 2000) and is thus expected to further enhance population build-up and expansion in O. communa (Chen et al 2014).…”

“…Insect performance or plant resistance is often tested by analyzing developmental time, weight, survival (Liu et al 2012) and herbivore damage (Stenberg and Muola 2017). These vital rates are important for a BCA's population density, and ultimately impact on the target plant invader (Augustinus et al 2020). For instance, faster developmental time allows more generations per year and a higher survival rate would directly result in higher population growth (Augustinus et al 2020), thus both will contribute to increased feeding damage and, together with leaf area removed (O'Neal et al 2002;Siemann and Rogers 2003) to increased biocontrol efficacy (Gassmann 1996;Lommen et al 2017b).…”

“…These vital rates are important for a BCA's population density, and ultimately impact on the target plant invader (Augustinus et al 2020). For instance, faster developmental time allows more generations per year and a higher survival rate would directly result in higher population growth (Augustinus et al 2020), thus both will contribute to increased feeding damage and, together with leaf area removed (O'Neal et al 2002;Siemann and Rogers 2003) to increased biocontrol efficacy (Gassmann 1996;Lommen et al 2017b). Specifically, we address the following questions: Is the plant-herbivore interaction driven (1) by the genotype of Ambrosia with some being resistant or at least highly unpalatable to all Ophraella genotypes?…”

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

“…However, if rising temperatures leads to reduced relative humidity, climate change may also have a negative effect on population build-up of O. communa. Laboratory studies revealed that relative humidity of less than 50% during the warmest time of the day significantly reduced egg hatching rates of this biological control agent (Augustinus and Sun et al 2020). Since biocontrol agent impact is dependent on high population densities (Myers andSarfraz 2017, McEvoy 2018), both temperature and humidity should be considered for models predicting O. communa impact on A. artemisiifolia (Augustinus and Sun et al 2020).…”